U.S. Depa rtm ent of Tran spo r ta tion
Federa l Av ia ti o n Administration 

# Advisory Circular

Subject: CE RTIFICAT ION OF PART 23 AIRPL A NES FOR FLIGHT IN ICING CONDITIONS Date: April 19, 2007 Initiated by: ACE-100 AC No: 23.1419-2D

FOREWORD

This adviso ry circu l ar (AC) sets forth an accep tab l e m eans of showing compliance with Title 14 Code of Federal Regulations (14 CFR), part 23, for the approval of airplane ice protection system s for operating in the icing envir onm ent defined by part 25, Appendix C.

S/Charles L. Sm alley

Charles L. S m alley Acting Manager, Sm all Airplane Directorate Aircraf t Cer tif ica tion Se rvice.4/19/07 AC 23.1419-2D

CONTE N T S

Paragraph Page

1. What is the purpose of this AC?

............................................................. 1 2. Who does this AC apply to?

................................................................... 1 3. Cancellation

............................................................................................ 1 4. Applicability

........................................................................................... 1

5. Related Regulations and Docum e nts

...................................................... 1 6. Related Reading Material

....................................................................... 3 7. Background

............................................................................................ 5 8. Planning

.................................................................................................. 5 9. Design Objectives

................................................................................... 6

10. Analyses and Ground Testing

................................................................ 6 11. Flight Test Planning

............................................................................... 18 12. Flight Tests

............................................................................................. 19

13. Perform a nce and Flying Qualities

.......................................................... 29 14. Ice Shedding

........................................................................................... 48

15. Placard i ng and AFM

.............................................................................. 49 16. Instructions for Continued Airworthiness

.............................................. 54 17. Ground Deicing Fluids

........................................................................... 62 Appendix 1 Definitions

.............................................................................................. A1-1 Appendix 2 Guidelines for Determ ining Cert ification Basis on Flight in Icing Approval STCs and Amended TCs.................................................... A2-1 Appendix 3 Guidelines for Supplem ental Type C e rtificates (S TC) and Am ended Type Certificates on Airplanes

.......................................... A3-1 Appendix 4 Guidelines for Certifying Ice Protection System s on Airplanes Not for Flight in Icing A pproval (“Non-Hazard” Basis)

................... A4-1 Appendix 5 Guidelines for Approval of Replacement Parts for Airfram e Deicing System s

................................................................................. A5-1 Appendix 6 Part 23 Subpart B Tests for Section 23.1419 at Am endm ent 23-43

...... A6-1 Appendix 7 Ice Contam inated Tailplane Stall

........................................................... A7-1 Appendix 8 AFM Li m itations and Norm al Procedures Sections

............................... A8-1

TABLES

Number Title P a g e

1 Fluid Capacity

.................................................................................. 16 2 Ice Accretio n Definition s

.................................................................... 33 3 Natural Icing Perform a nce and Handling Qualities Tests

................... 39 4 Flight Test Tolerances

......................................................................... 40 5 Failure Ice Accretion Flight Tests

....................................................... 45 5-1 Summ ary of Test Requi rem e nts for Replacem ent of Airfram e De icing Com p onents

....................................................... A5-1 6-1 Part 23 Subpart B Tests for S ection 23.1419 at Am endm ent 23-43

... A6-1

iii (and iv )4/19/07 AC 23.1419-2D

1. What is the purpose of this AC? This Advisory Circular (AC) sets forth an acceptable

m eans, but not the only m eans, of demonstrating com p liance with the ice protection requirem e nts in Title 14 of the Code of Federal Regulati ons (14 CFR) part 23. The Federal Aviation Adm i nistration (FAA) will consider other m e thods of de m o nstrati ng com p liance that an applicant

m a y elect to present. Th is m a terial is neithe r m a ndatory nor regulatory in nature and does not constitute a regulation.

2. Who does this AC apply to? The guidance provided in this docum ent is directed to airp lane

m a nufacturers, m odifiers, foreign regulatory authorities, and FAA s m all airplane type certification engineers, and their designees. This AC applies to airplane ice protection system s in
any norm a l, utility, acrobatic or co mmuter category part 23 airplane.

3. Cancellat i o n . AC 23.1419-2C, Certification of Part 23 Airplanes for Flight in Icing Conditions, dated July 21, 2004, and AC 23.143-1, I ce Contam inated Tailplane Stall (ICTS), dated December 20, 2001, are can celed. In add ition, a ll po licy related to th e certification of ice protection system s on part 23 airplanes, issued prior to this AC, and is superseded by this AC.

4. Applicabilit y . The guidance provided here applies to the approval of airp lane ice protection system s for operating in the icing environm ent defined by part 25, Appendix C. The guidance should be applied to new Type Certif icates (TCs ), Supplem ental Type Certificates (ST C s), and

am endm ents to existing TCs for airplanes under part 3 of the Ci vil Aviation Regulations (CAR) or its predecessor regulations, and part 23, fo r which approval under the provisions of § 23.1419 is desired.

5. Related Regulations and Documents.

a. Regulations. By their adoption in am endment 23- 14, which shows their requirem e nts are directly related, §§ 23.929, 23.1309, and 23.1419 are appli cable to a part 23 airplane icing certification program regardless of the cer tif ica tio n basis f o r the ba sic airplane; however, for those airplanes certificated in accord ance with part 3 of the CAR or earlier, and through part 23 at

am endm ent 23-13, the application of these sections m a y be lim ited to the equipm ent being used for ice protection. Som e system s that were previ ously approved on the airplane m a y need to be modified to im prove their reliability when those system s are utilized as part of that airplane' s icing approval.

(1) W ith the adoption of amendm ent 23-43, § 23.1419 was revised to do the f o llowing: to spec if y that the p e rf or

m a nce, controllabilit y, m a neuverability, and stability m u st not be less than that required by subpart B of part 23; add the requirem e nt for flight testing in m e asured, natural icing conditions; provide specific test requirem ents; clarify the requirem ents for inform ation that m u st be provided to the pilot, and allow approval of equi valent com p onents that have been previously tested and approved, and that have dem onstrated satisfactory service if the insta lla tions are sim ilar.

1AC 23.1419-2D 4/19/07
(2) Prior to the adoption of am endm ent 23-43, so m e part 23 airplanes were certificated for flight in icing using § 25.1419.

(3) In addition to the previously m e ntioned requirem e nts (§§ 23.929, 23.1309, and 23.1419), other sections should be applied depending upon the ice protection system design and the original certification basis of the airplane. Refer to AC 20-73A, Appendix C, Table C-2. Many of the requirem e nts in Table C

- 2 of AC 20- 73A are also applicable, even without approval for flight in icing conditions. Further guidance on establishing a certification basis for flight in icing approval can be found in Appendix 2 of this AC.

b. ACs. Copies of current editions of the follo wing publications m a y be downloaded from the FAA' s Regulato r y an d Guidance Library (RGL) www.rgl.faa.gov or obtained from the U.S. Departm e nt of Transportation, Subsequent Dist ribution Office, Ardm ore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785:

AC 20-73A “Aircraft Ice Protection,” August 16, 2006.

AC 20-115B “Radio Technical Commissi on for A e ronautic, Inc. Docum e nt RTCA/DO-178B,” January 11, 1993.

AC 20-117 “Hazards Fo llowing Gro und De icing and Ground Operations in Conditions Conducive to Airc raft Icing,” December 3, 1982.

AC 20-147 “Turbojet, Turboprop, and Turbof an Engine Induction System Icing and Ice Ingestion,” February 2, 2004.

AC 21-16E “RTCA Docum e nt DO-160E, E nviro nm ental con d itions and Test Procedures f o r Airborne Equipm ent,” Decem ber 20, 2005.

AC 21-40 “Application Guide for Obtaining a Supplem ental Type Certification,” May 6, 1998.

AC 21.101-1 “Change 1, Establishing th e Certification Basis of Changed Aeronautical Produc ts,” April 28, 2003.

AC 23-16A “Powerplant Guide for Certif ication of Part 23 Airplanes and Airships,” F e bruary 23, 2004.

AC 23-17B “System s and Equipm ent Guide for Certification of Part 23 Airplanes,” February 23, 2004.

AC 23.629-1B “Means of Com p liance with Titl e 14 CFR, Part 23, § 23.629, Flutter,” Septem ber 28, 2004.

24/19/07 AC 23.1419-2D

AC 23.1309-1C “Equipm ent, System s, and Insta llations in Part 23 Airplanes,” March 23, March 12, 1999.

AC 91-74 “Pilot Guid e Flight in Icing Conditio ns,” December 12, 2002

.

AC 120-58 “Pilot Guide Large Aircraft Ground Deicing,” Septem ber 30, 1992.

AC 120-60B “Ground Deicing and A n ti-icing P r o g ram , ” December 20, 2004.

AC 135-16 Ground Deicing & Anti-icing Training & Checking,” December 12, 1994.

AC 135-17 Pilot Guide-Sm all Aircraft Gr ound Deicing (pocket),” December 14, 1994.

Copies of the current A C m a y be purchased from the Superintendent of Docum e nts, P.O. Box 371954, Pittsburgh, PA 15250-7954. Make check or m one y order payable to the Superintendent of Docum e nts:

AC 23-8B “Flight Test Guide for Certif ication of Part 23 Airplanes,” A ugust 14, 2003.

6. Related Reading Material.

a. FAA Orders.

FAA Order 8110.4C, “Type Certif ication,” October 26, 2005.

b. FAA Technical Reports. The following FAA technical re ports can be obtained from the National Technical Inform ation Serv ice in Springfield, Virginia 22161:

(1) FAA Technical Report DOT/FAA/CT-88/ 8, "Aircraft Icing Handbook" (March 1991), includes reference m a terial on ground and ai rborne icing facilities , sim u lation procedures, and analytical techniques. This docum ent repres ents all types and classes of aircraft and is intended as a working tool for th e designer and analyst of ice prot ection system s. Updates can be found on the FAA Technical Center web site:

http://aar400.tc.faa.gov/P r ogram s/FlightSafety/icing/eaihbk.htm

(2) FAA Technical Report ADS-4, "Engineering Sum m a ry of Airfram e Icing Technica l Data," and Report No., FAA-RD-77-76, "Engineeri ng Summary of Powerplant Icing Technical Data," provide technical inform ation on airfram e and engine icing conditions, and m e thods of detecting, preventing, and rem ovi ng ice accretion on airfram e s and engines in flight. A lthough most of the infor m ation contained in ADS-4 a nd FAA-RD-77-76 reports is still valid, som e is

3AC 23.1419-2D 4/19/07
outdated, an d m o re usable inform ation is now availab l e th rou gh recen t res earch and ex perien ce, and is included in the Aircraft Icing Handbook.

(3) FAA Technical Report DOT/FAA/AR-01/91, "A History and Interpretation of Aircraf t Icin g Intens ity Def i nitions and FAA Ru les f o r Oper ating in Ic in g Condition s " (Novem b er 2001), provides a good reference for unders tanding icing operational rules.

(4) FAA Technical Report DOT/FAA/AR-02/68, "E ffe ct of Residual and Intercycle Ice Accretions on Airfoil Perfor m ance" (May 2002), details icing tunnel te sting to determ ine intercycle and residual ice on a 23012 airfoil, and wind tunnel testing of uniform sandpaper and inte rcycle ic e shapes.

(5) FAA Technical Report DOT/FAA/CT-TN86/ 11, “Fluid Ice P r otection System s,” July 1986.

(6) National Aeronautics an d Space Adm i nistration (NASA)/TP—2000-209908, “NASA/FAA Tailplane Icing Prog ram : Flight Test Report” (M arch 2000), provides reference inform ation on Ice Contam inated Tailplane Sta ll (ICTS). Assumptions, ice shapes, and certain other data are not necessarily representative or ap propriate for use with ot her projects. The above report and other reference m a terial on ICTS ar e also availab l e at the NASA Glenn Research Center Icing Branch website: icebox.grc.nasa.gov.

c. Technical S t andard Order (TSO): A copy of the current edition of the following publication m a y be obtained from the Federal Av iation Administration, Ai rcraft Certification Service, Aircraft Engineering Division, Tec hnical Program s and Continued Airworthiness Branch—AIR-120, 800 Independence Avenue, SW , W a shington, DC 20591 or from t h e FAA website at www.faa.gov:

TSO-C16 “Air-Speed Tubes (Elect rically Heated),” September 1, 1948.

TSO-C16a “Electrically Heated Pitot and Pitot-S t atic Tubes,” October 6, 2006.

TSO-C54 “Stall W a rning Instrum e nts,” October 15, 1961.

d. SAE Documents. The Society of Autom o tive Engineers (S AE), Inc. Aerospace Recommended Practice (ARP) and Aerospace Info rm ation Report (AIR) docum e nts are available from SAE, 400 Comm onwealth Drive, W a rrendale, PA 15096-0001 or from their website at
www.sae.org:

ARP4761 “Guidelines and Me thods for Conducting the Safe ty Assessm ent Process on Civil Airbo r ne System s and Equipment,” Decem ber 1, 1996.

AIR4367 “Aircraft Ice Detectors and Icing Rate Measuring Instrum e nts, “April 1, 1995.

44/19/07 AC 23.1419-2D

AIR5504 “Aircraft Inflight Ic ing T e rm inology,” Septem ber 17, 2002.

AIR1168/V1 “Ice, Rain, F og, and Frost Prot ection,” July 1, 1989, part of “Applied Therm odyna m i cs Manual,” Septem ber 1, 1992.

. ARP4087 “ W ing Inspection Lights – Design Criteria,” September 12, 2006.

AS393 “Airspeed T ubes Electrically Heated,” August 14, 2002.

AS8006 “Minim um Perform a nce Standard for Pitot and P itot S t atic T ubes, “April 28, 1988.

AS403 “Stall W a rning Instrum e nt,” July 15, 1958.

The SAE and a working group for Task 11A of th e FAA Inflight Aircra ft Icing Plan have developed the following docum ents:

ARP5903 “Droplet Impingem e nt and Ice Accretion Com put er Codes, October 16, 2003.

ARP5904 “Airborne Icing Tankers,” October 21, 2002.

ARP5905 “Calibration and Acceptance of Icin g W i nd Tunnels,” Sep t ember 18, 2003.

e. Miscellaneo u s Documents.

(1) British Sp ecification (B S) 2G-135, “Specifi cation for Electrically -Heated Pitot and Pitotstatic P r essure Heads,” 1967.

(2) Am erican Society for T e sting and Mate rials (A STM) G76-95, “Standard Test Method for Conducting Erosion Tests by Solid P a rticle Im pingem e nt Using Gas Jets”

7. Background.

AC 20-73A contains a detailed history of ice protection regula tions for part 23 airplanes.

8. Planning.

a. Flight in Icing Approval. The applicant shou ld subm it a cer tification plan in accordance with FAA Order 8110.4C and AC 20-73A. The cer tification plan should describe all of the applicant' s efforts intended to lead to certification. This pl an should identify, by item to be certificated, the certificat ion m e thods that the app licant intends to use. It should provide for a certification checklist. R e garding § 23.1419, it shoul d clearly identify analyses and tests, or references to sim ilarity of desi gns that the applicant intends for certification of the ice protection system . These m e thods of showing com p liance should be agreed upon betw een the applicant and the FAA early in th e typ e cer tif ica tio n program

. Detailed guidance for STCs or am e nded TCs on

5AC 23.1419-2D 4/19/07
part 23 airplanes approved for f light in icing can be found in A ppendix 3 of this AC. It is im perative that the applicant obtains FAA concu rrence prior to conducting certification tests.

b. Installation s w i thout Flig ht in Icing Approval. There m a y be tim es when applicants

m a y want to certificate an ice pro t ection system installation but do not want to obtain flight in icing approval. In the past thes e system s have been called “non-ha zard” installations. This m e ans that the aircraft is prohibited from flight in icing conditions bu t the r e is so m e ice protec tion to f acilitate an exit from an inadvertent icing encount er. Guidance for the approval of these types of ice protection system s can be found in Appendix 4 of this AC.

c. Replacement Parts for Airframe I ce Protectio n Systems. The requirem e nts leading to approval of replacem ent airfram e deicing systems or airfram e therm a l deicing or anti-icing system s are detailed in Appendix 5 of this AC.

9. Design Objectiv es. The applicant must dem o nstrat e by analyses and tests that the airplane is capable of safely operating thr oughout the icing envelope of part 25, Appendix C. The envelope can be reduced for airplane s certificated for operation where systems or perform a nce lim itations (e.g., altitude), not related to ice protection, exist.

10. Analyses and Ground Testing. The applicant no rm ally prepares analyses to substantiate decisions involvi ng app l ication of selected ice p r otection equ i pm ent and to substantiate decisions to leave norm a lly prot ected areas and com ponent s unprotected. Such analyses sho u ld clearly s t ate the bas i c pr otection required, the assum p tions m a de, and delineate the m e thods of analysis used. All an alyses should be validated either by tests or by

m e thods agreed to by the FAA. Thi s subs tantiation should include a discussion of the

assum p tions m a de in the analyses and the design provisions include d to c o m p ensate f o r these assumptions. Analyses are norm a lly used for the following:

a. Areas and Components to be Protected. The applicant should ex am ine the areas listed in AC 20-73A to determ ine the degree of protection required.

An applicant m a y find t h at protection is not re quired for one or m o re of t h ese areas and

com ponents. If so, the applicant should include supporting data and rationale in the analysis for allowing them to go unprotected. The applicant should dem o nstr ate that allowing them to go unprotected does not adversely affect the ha ndling or performance of the airplane.

b. Ice Accretion Analyses.

(1) Impingeme n t Limit An alyses. The applicant should prepare a drop im pingem e nt and water catch analysis of the wing, horizontal a nd vertical stabilizers, propellers, and any other leading edges or protuberances su ch as antennas that m a y require protection. This analysis should consider the various airplane ope rational configurations and associated angles of attack. This analys is is n eeded to establish the upper and low e r aft droplet im pinge m e nt lim its that can then be used to es tablish th e aft ice form ation lim it a nd the exten t of the pro t ectio n surface co verage

64/19/07 AC 23.1419-2D
needed. The applicant should c onsult AC 20-73A, “Aircraft Ice Pr otection” for m o re detailed inform ation.

(2) Critica l Ice Accretions. The critical ice accre tion s for which operational characteristics are to be evaluated sh ould be de term ined for each flight ph ase as discus sed in paragraph 13.b. of this AC. The pa ram e ters to be considered are th e flight conditions (e.g., airp lane con f iguration, airspeed, angle of attac k, altitude) and the ici ng con d itions of part 25, Appendix C (tem perature, liquid water content, m ean effectiv e drop diam eter). The applican t should substantiate the critical m ean effective drop diam eter, Liquid W a ter Content (LWC), and
tem p erature that result in the form ation of an ice accretion th at is cri tical to the airp lane' s operational characteristics. For deicing system s, intercycle, residual, and runback ice accre tions should be considered.

(3) The 45-Minute Hold C o ndition. The 45-m i nute hold criterion should be evaluated when determ ining critical ice shapes for whic h the operation a l characteristics of th e o v erall airplane are to be analyzed. S ee AC 20-73A for m o re inform ation.

(a) A m ean effective d r oplet diam eter of 22 m i crons and a liquid water content of 0.5 gm / m 3 with no horizontal extent co rrection are norm a lly used for this analys is; h o wever, the applic ant sh ould substan tia te the spe c if ic valu es used, including tem p erature, which represent the critical conditions for the airpla ne' s perform a nce and handling quali ties. Critical flight conditions should be considered such as we ight and speed for critical angl e of attack, a nd airspeed and altitude for m a xi m u m water catch. For exam pl e, m i nim u m holding speed should be evaluated, but a higher airspeed that the airplan e m a y operate at m a y be more critical because of the lower angle of attack and higher water catch.

(b) The critical ice shapes derived from this analysis should be compared to critical shapes derived from other analyses (clim b, cruise , and descent, approach) to establish the m o st critica l sim u lated ice sh a p es to be used during dry air flight tests.

c. Airframe.

(1) Structural Analyses.

(a) The structural analyses should include an alyses which establis h that critical ice build-ups on antennas, m a sts, and other com ponent s attached externally to the airplane do not result in ha z a rds. Fligh t tests in sim u lated o r natu ral icing con d itions o r with sim u lated ice shap es

m a y be used to substantiate the structural an alyse s ; however s i m ilarity to previous approved designs is a common m e thod of compliance.

(b) Determ ine that the tem p eratu r e gradie nt produced on heated windshields does not adversely affect windshi eld structural integrity.

(2) Flutter Ana l yses. AC 23.629-1B, “Means of Com p liance with Title 14 CFR, Part 23, § 23.629, Flutter,” provides guidance for show ing com p liance with § 23.629. The flutter

7AC 23.1419-2D 4/19/07
analyses should reflect any m a ss accum ulations on unprotected and protected surfaces from exposure to part 25, App e ndix C icin g conditions, includ ing any accretion s that could develop on control surfaces. The 45-m inute hold should also be considered. Ice accretions due to failure of the ice protection system should also be addressed.

d. Pow er Sources.

(1) Pow er Source Analysis. The applicants should evalua te the power sources in their ice protection system design. Elec trical, bleed air, and pneum atic sources are norm a lly used. A load analysis or test should be conducted on each power source to d e term ine that th e power source is adequate to supply th e ice protection system , plus a ll other essential loads throughout the airplan e flight envelo pe unde r co nditions req u iring op eration of the ice protection system

.
(2) Effect on E ssentia l Sys t ems. The effect of an ice protection system component failure on po wer availability to ot her essential loads should be ev aluated, and any resultant hazard should be prevented on multi-eng i ne designs an d m i nim i zed on single-en gine des i gns . The applicant sh ould show that there is no hazard to the airplan e in the ev ent of any power source failure during flight in icing c onditions. Two separate power sources (installed so that the failure of one source does not af fect the ability of th e rem a ining source to provide system power) are adequate if the single so urce can car ry all the e s s e ntia l load s.

(a) Tw o-Engine Airplanes require two sources in a ccordance with § 23.1309(c). All power s ources th at a f f ect engine or engine ic e prote c tion system s f o r multi-eng i ne airp lanes
must com p l y with the engine isolation requirements of § 23.903(c).

(b) Single-Engine Airplanes . Section 23.1309(a) require s that the ice protection system be designed to minim i ze hazards to the ai rplane in the event of a probable m a lfunction or failure. Failure condition classifi cations of “ m ajor”, “hazardous” or “catastrophic” are considered hazards. Co mplete los s of the airfram e ice protec tion sys t em has been co nsidered at least “m ajor” on past single engine certification program s

. Since experience has shown that the failure of
genera tors c u rrently in s e rvic e is p r o b able, f o r ex am ple, system s that utilize a gene rator, such as an alternator, would require two s ources of electrical power. This is also consistent w ith past project specific guidance on interp retation of § 23.1309, which stated th at the level of safety in a single engine airplane is estab lished by engine reliability and th e ice protection system should not

com p rom i se it. For other types of power sources

, additional r e liab i lity evaluation of the power source under system loads and environm ental co nditions m a y be required if a single source system is planned.

(c) Load Shedding. Determ ine if load sheddi ng can be accom p lished after a partial failure condition. If app licable, a load shedding sequence should be provided so the pilot

m a y assure that adequate power is available to the ice protection equipm ent and other necessary equipm ent for flight in icing conditions.

(3) Electro mag n etic Comp atibility. T h e effect, if any, of ice protection system operation on other airplane system s must be determ ined to show com p liance to § 23.1309(a).

84/19/07 AC 23.1419-2D

(a) Designs should m i ni m i ze Magnetic Direct ion Indicator (MD I) deviations. If the ice protection system causes greater than an l0-degree deviation, then the placard requirem e nt of § 23.1327 (am e ndm e nt 23-20) should be applied in lieu of previous requirem ents. Refer to AC 23-17B f o r guidance on using a m a gnetic compass as a m itigating f actor in a sy stem saf e ty

assessm ent for cockpit heading display.

e. Failure Analysis. AC 23.1309-1C provides guidance a nd infor m ation for an acceptable

m eans, but not the only m eans, for showing co mpliance with the requir em ents of § 23.1309(a) and (b) (am e ndm e nt 23-49) for equipm ent, syst em s, and installations in 14 CFR, part 23 airplanes. T h e regulatory requirem e nts ar e in § 23.1309. Substant iation of the hazard classification of ice protecti on system failure conditions is typically accom plished through analyses and / or testing. It has been s t anda rd indu stry practice to assign a probability of encounterin g icing cond itions of “on e” for an ai rplane certificated for flight in icing.

(1) During the analyses, each identifiable failu re within the system should be exam ined for its effect on the airplane and its occupants. E x am ples of failu res th at need to be exam ined include :

(a) Those that allow an ice s h ap e to accrete in size g r eater than design levels , to accrete asy mmetrically, or accrete in ar eas that were norm a lly protected ; or

(b) System failures such as loss of pneum atic boot vacuum , overheat of a therm a l system , or leak in a hot air bleed air line.

(2) A probable m a lfunction or failure is a ny single malfunction or failure that is expected to occur during the life of any single airplane of a specific type. This m a y be determ ined on the basis of past service experi ence with sim i lar com ponents in com p arable airp lane app lications. T h is definitio n should be extended to multiple m a lfunctions or failure when: (a) The first m a lfunction or failure would not be detected during norm a l operation of the system, including periodic ch ecks establis hed at in terv als th at are consisten t with the degree of hazard in volved; o r

(b) The first m a lfunction would inevitably lead to other m a lfunctions or failures. A procedure requiring a pilot to ex it icing conditions would not be acceptable after an y failure condition that would becom e catas trophic within the av erage exposure time it takes to exit icing conditions.

(3) Pow er Source Failure. Assure that no probable failu re or malfunction of any power source (electrical, fluid, bleed air, pn eum a tic, and so f o rth) will im pair the ability of th e rem a ining source(s) to supply adequate power to system s essential to safe opera tion during icing flight.

9AC 23.1419-2D 4/19/07
(4) Failure Annunciations. W a rning infor m ation must be provided to alert the crew to unsafe system operating conditions and to enable th em to take appropriate corrective action in accordan ce with § 23.1309(b)(3 ).

(a) The requirem e nt for warning inform a tion in § 23.1309(b)(3) is dependent on the seve rity of the f a ilur e , not depen d ent on the probability of the f a ilur e

.
(b) A m eans to indicate to th e crew that the ice p r otection sys t em is rece iving adequate electrical power, bleed air pressure, vacuum , or flui d pum p output, and so forth, as appropriate, and it is functioning norm a lly. An nunciation would not be required for obvious, inherent failures, such as failu re of a fluid windshield system

.
(c) Means to in dicate that the pneum atic deic ing boot system is receiving adequate pressure is required in accordance with § 23.1416.

1. The boots should be shown to operate at the pressure threshold of the annunciation.

2. Annunciation when the boots are receiv ing adequate pressure has been used in previous certifications . For boots that cycle autom a ti cally, annunciation lights m a y be provided when the boots are not r eceiving adequate pressure when commanded, in lieu of lights that illum i na te dur ing ea ch inf l ation cycle. This prom otes the dark cockp it conc ept, a nd it’s eas ier to detect the presence of a light rather than the abs e nce of a lig ht.

3. Annunciations of failures should be consistent w ith § 23.1309(b)(3) and § 23.1322.

(5) Circuit and Protective Devices.

(a) Determ ine that the d e sig n incorporates electrical overload pr otection that opens regardless of operating control position.

(b) Verify that the design is such that no protective device is protecting m o re than one circuit essential to continued safe flight (for exam ple, pitot heat and stall warning transducer heat are considered separate e ssential circuits and should be provided sepa rate protection).

(c) Ice protection m onitor and wa rning circuits should be considered separate from
contro l circu its and each should provi de indiv i dual circuit protection.

(d) On airplanes equipped with dual power sources, a power distribution system having a single bus and a single circuit breaker protecting the ice prot ection system is not acceptable.

(6) Windshield Heat Systems. There are requirem ents in § 23.775(g). A probable single failure of a transparency heating system should not adversel y affect the integrity of the airp lane cab in or create a potential danger of fire.

104/19/07 AC 23.1419-2D

f. Similarity Analyses.

(1) In the c a se o f certif ica tio n based on s i m ilari ties to other type ce rtificated airplanes previously approved for flight in icing conditions, the applican t should specify the reference airplane m o del and the com ponent to which the refe rence applies. Specific sim ilarities should be shown for physical, functional, thermodynam i c, pneum a tic, aerodynam i c, and environm ental areas. Analyses should be conducted to show th at the com p onent installation and operation is equivalent to the previous ly approved installation.

(2) Sim ilarity requires an evaluation of both th e system and installation differences that

m a y adversely affect the system perform ance. An assessm ent of a new installation should consider differences affecting the aircraft and the system . Sim ilar ity m a y be used as the basis for certification without th e need for add ition a l tests provided :

(a) Only m i nimal dif f e rence s exist b e tw een the p r ev iously c e rtif icated sys t e m and installation, and the system and in stallation to be certificated; and

(b) The previou s ly certificated system a nd installation have no unresolved icing related service history problem s.

(3) FAA Order 8110.4C should be consulted rega rding the use of pr eviously approved FAA data.

(4) If there is un certainty ab out the ef f e c t s of the dif f e rence s , add ition a l tests or analyses, o r both, should be conducted as necessary and appro p riate to resolve the op en issues.

g. Induction Air System Protection. The induction air system fo r airplanes is certificated for ice pro t ection in acco rdance with § 23.1093. Thes e requ irem ents are for all airplan e s even those not certificated for flight in icing conditions. Thus i ce protection system s installed on previously type certificated airplanes to prot ect the engine inducti on air system should be adequate and need not be re-exam i ned, unless the in let is being m odified, th e original certification basis is inad equate, o r a n in-f ligh t AFM lim itatio n was used to com p ly with the f a lling and blowing snow regulation. W h en natural icing f light tests are conducted to show com p liance to § 23.1419, engine operation, engine ice protection system procedures, and engine inlet ice

accre tion sh ould be eva l uated if flig ht tes t s in m easured, n a tural icing co nditions we re not previously accom p lished on the engine/inlet conf iguration. S ee AC 23-16A and AC 20-147 for more information.

(1) Engine Ice Protection – Flight Idle. Turbojet engine ice protection should be
autom a tic once the eng i ne ice p r otection sys t em is activated. The engine mu st be protected from ice with the throttle against the idle stop, which m a y require an auto m a tic increase in thrust when the engine ice protection system is activated.

11AC 23.1419-2D 4/19/07
(2) Delay of Icing Approval. Manufacturers have chosen to delay showing com p liance to § 23.1419, and therefore receive flight in icing approval, un til after typ e certification

. The

m a in reason is usually not to dela y obtaining type certifi cation of the basic ai rp lane for m a rketing or contractual reasons. The ai rplane is prohibited from fli ght in known or forecast icing conditions u n til a findin g of com p liance to § 23. 1419 is m a de. However, the airplan e m a y inadvertently encounter icing cond itions, and the engines should operate without a sustained loss of power and there should not be a need to sh utdown an engine in flight. Com p liance to § 23.1093 is required for basic type certification, and the eng i ne as a result will h a ve ice protection capability. A n exam ple would be an ice protection system for the engine inlet. Airfram e ice protection system s can be considered part of the engine ice protection system if the possibility exists of ice accre ting on the airfram e in an inadvertent encounter and shedding into the engines. An exa m ple is ice accreting on th e inboard wing of airpla ne s with af t f u selage mounted engines. Applicants who delay icing certification u n til after typ e certificatio n m u st show com p liance to § 23.901(d) by one of the following m e thods:

(a) A trajectory analysis, supplem e nted by f light testing in m e asured natural icing or flight testing behind an airbor ne icing tanker, as described in paragraph 14 of this AC, to show the am ount of ice that accretes in five m i nut es at critical part 25, Appendix C continuous

m a xi m u m c onditions does not shed into any engine; or

(b) Analysis wh ich shows th e m a ss of ice that accretes in five m i nutes in critical part 25, App e ndix C continuous m a ximum conditions is less th an the m a ss of ice shown to be ingested by the engine for com p liance to § 33.77. This analysis should assum e :

1. The spanwis e length of the ice sh ape is the m a ximum length that can be ingested without striking the inlet lip or engine spinner.

2. The ice shap e on the win g leading ed ge does not break cho r d w ise, i.e., the ice abov e and below the stagna tion line should be considered.

3. In lieu of five m i nutes of ice accre tion, credit can be used for operational ice pro t ec tio n system s, with the ex c e ption in pa r a graph (4 ). The m o st critica l of the f o llowing should be used:

(aa) Two m i nutes representing de layed system activation;

(bb) Inter c ycle/r e s idual ice f o r de icing system s for ope rating speeds above 160 Knots Calibrated Airs peed (KCAS). Below 160 KCAS, e m pirical data should substantiate that deicing syst em s shed ice at each cycle.

(cc) Runback ice in 5 m i nutes for therm a l system s.

4. Flight testin g in m easured natura l icing or flight testing behind an airborne icing tanker would be re quired for novel ice pr otection system s, such as the graphite therm a l deic ing system

.

124/19/07 AC 23.1419-2D
h. Propeller Ice Protection.

(1) An analysis should be provided for pa rt 25, Appendix C icing conditions that:

(a) Substantiates the chordw ise and spanwise ice protection coverage

(b) Substantiates the ice protection sy stem power density or fluid rate

(c) Calculates intercy c le ice accretions and resulting efficiency lo sses.

(2) See AC 20-73A for additional gui dance on propeller analysis.

i. Pitot Probe Ice Protection.

(1) Conditions Within the Part 25, Appendix C Icing Envelope.

(a) Airplanes I n corporatin g Airspeed Systems With TSO C16 Authori z ations. Com p liance to the TSO- C16 qualif ic ation s t andard for elec trically heated pitot probes is not sufficient by itself in demonstrating com p liance to the installation requirem e nts of § 23.1309(b)(1) and § 23.1419. Section 23.1309(b)(1) requ ires that the system m u st perform its intended function under any foreseeable operatin g condition. Section 23. 1419 requires that an airplane certificated for f light in icing m u st be able to safe ly operate in part 25, Appendix C icing conditions. It is un lik ely that the con d itions of part 25, Appen d ix C that are critical to the air d a ta system equipm ent will b e encountered during flig ht tes t s. Although functioning of pitot probes are evaluated in natural icing conditions duri ng certification test pr ograms, there is no requirem e nt to flight test at the p a rt 2 5, Appe ndix C icing lim i ts becaus e th e low probability of finding those conditions im poses a burden. TSO C16, Air-speed tubes (electrically heated) require compliance to the perform a nce specifications of SAE Aer onautical Standard AS393. This standard and AS393A (out -of-date), are non-current. SAE AS 393A includes a test to dem onstrate deicing and anti-icing capability, but only tem p erature and airspeed are sp ecified. Liq u id water content is no t spec if ied b u t it inf l uenc es heat re quirem e nts. Consequently certification program s should supplem ent the icing flight te sts with an icing tunnel test a nd/or airborne icing tanker test data, as n ecessary, or reference tes tin g th at has been accom p lished by the pitot p r obe

m a nufacturer, or show sim ilarity to a sim ilar, icing approved airplane with no negative service history. In-service experience du ring severe atm o spheric conditi ons has shown that pitot tubes qualified to the older standards have resulted in airspeed fluctua tions and even loss of indicated airspeed. As these com ponents should perfor m as intended in all expected atm o spheric environm ents, it is reaso n able to req u ire that th ey be qualified to the Con tinuous and interm ittent

m a xi m u m icing conditions defined in part 25, A ppendix C.

(b) Airplanes Incorporatin g Ai rspeed Systems With TSO C16a Authori z ations. TSO C16a, Electrically heated pitot a nd pitot-static tubes, references SAE Aeronautical Standard AS8006 and supplem ents the icing requirem e nts with specific part 25, Appendix C icing co nditions and speci fic liq uid water co ntent tests from British S p ecif ica tion (BS) 2G.135 “Specification for El ectrically-Heated Pitot and P itot-S t atic Pressure Heads”

.

13AC 23.1419-2D 4/19/07
Analysis, icing tunnel tests, or f light tests dedicated to probe h eat evaluation, are not required. See paragraph 12.c.(3) for air data system evalua tions that are accom p lishe d during a natural icing flight test program

.
(2) Conditions Outside of the Pa rt 25, Appendix C Icing Envelope. Although part 25, Appendix C only considers the liquid water content of icing condi tions, recent cloud characterization research has i ndicated that approxim ately 40 pe rcent of icing condition events consist of liquid water drops and ice crystals (m ix ed phase icing conditions). The operating rules do not prohibit operations in m i xed phase and ice crystal icing conditions. The incident history indicates that flightcrews have experienced tem porary loss of or m i sleading airspeed indications in icing. It is likely that som e of these incidents were due to ice crystals. Pitot tubes are m ounted such that they typically are high efficiency collectors of ice crysta ls. Encountering high concentrations of ice crystals can lead to bloc ked pitot p r obes as the en erg y requir e d to m e lt the ice crystals can exceed Appendix C design requ irem ents.. More recent s t andards ind i cate that these com ponents should be qualified for opera tion in atm o spheric conditions beyond the environm ent described by part 25, A ppendix C, specifically during ice crystal and m i xed phase icing conditions. R ecently, som e aircraft m a nufacturers and f o reign certification auth orities hav e required pitot and pitot-static prob es to be tested in ice crystal and m i xed phase icing conditions along with supercooled liquid wate r conditions. As a result, som e pitot tube m a nufacturers now use the icing environm ent of British Specificatio n (BS) 2G.135 “Specification for ElectricallyHeated Pito t and Pitot-Static P r essure Heads,” as modified by the m a xi m u m rate that the icing tunnel facility can produ ce ice crys tal, in add itio n to the requirem e nts of the TSO. Even though the part 23 and part 25 regulations only address li quid water and testing in the m i xed phase or ice crystal conditions are not required for FAA approval, it is goo d design pra c tic e to as su re the p ito t heat is sufficient for the ice crystal and m i xed phase conditions of BS 2G.135.

j. Stall Warn i ng Ice Protection. Co mpliance to the TSO qualif ica tion s t a ndard f o r sta ll warning instrum e nts (TSO-C54) is not sufficien t by itse l f in d e m onstratin g com p liance to the installation requirem e nts of § 23.1309(b)(1) and § 23.1419.

(1) Conditions Within the Part 25, Appendix C Icing Envelope. TSO-C54, “Stall W a rning Ins t rum e nts”

, requires compliance to the pe rform a nce specifications of SAE Aeronautical Standard AS403A with som e ex ceptions and additions. This standard is noncurrent. As in AS393A, the requirem ents include a test to dem onstrat e deicing and anti-icing capability, b u t only tem p eratu r e and airspeed are specified

. The p recipitation test conditions of AS403A include m oderate icing con d itions for T ype II in stru m e nts. However, "m oderate" is no t defined. The sam e comm ents from 9i (1) apply. The applicant is responsible for showing that stall warning heat is ade quate throughout the part 25, Appendix C icing envelope.

(2) Conditions Outside of the Part 25, Appendix C Icing Envelope. The sam e comments from paragraph 10i(2) above apply to stall warning ice protection system s.

k. Static Press u re Systems. Each static port design or location should be such that

corre lation b e tween air p r essur e in th e sta tic sy ste m and true ambient pressure is not altered when flying in icing conditions. Means of showi ng compliance include the following: anti-icing

144/19/07 AC 23.1419-2D
devices, alternate sou r ce for static pressure, or demonstration by test that port icing does not occur under any condition. W h ere th e port is therm a lly protected, a therm a l evaluation shou ld be conducted to dem onstrate that the protection is adequate.

l. Ice Detec t io n

(1) Regulation. Requirem e nts for ice detection are in § 23.1419(d).

(a) A m eans m u st be identified or provi ded, and described in the AFM, for identifying ice accretion.

(b) Adequate lighting m u st be provi ded for ice detection at night.

1. An ice inspe c tion light th at illum i nates a reference surface or a wing leading edge is norm a lly provided.

2. A hand-held flashligh t is not accep table as ice detection light.

(2) Ice Detec t io n System. Besides the pilot' s appraisal of icing conditions (i.e., defined by tem p erature and visible m o isture or visual de tection of ice accretion s on wiper blades, window fra m es or propeller spinner, etc.), som e airplanes use Flight Ice Detection System s (FIDS). FIDS

m a y either directly detect the p r esence of ice on an airp lane reference surf ace or detect that the airplane is in icing conditions. Ther e are basically two class e s of FIDS:

(a) Advisory Flight Ice Detection System. An advisory FIDS provides inform ation to advise the flightcrew of the pr esence of ice accretion or icing conditions. The flight crew has prim ary responsibility for detect in g icing cond itions o r ice accretions, u s ing the

m eans defined in the AF M, and activating the Ice Protection System s (IPSs). Advisory FIDS can
autom a tically activ ate th e IPS. However, th e AFM m u st state the fligh t crew has prim ary responsib ility for detecting icing con d itions o r ice accretion s

.
(b) Primary Flight Ice Detection System. A Prim a r y FIDS (PFIDS) is considered the sole m eans used to d e term ine when the IPS must be activated. The IPS m a y be
autom a tically activ ated b y the PFIDS or the PFID S m a y provide a flight deck signal that will direct the crew to m a nua lly ac tiva t e the IPS.

(c) Certif icat io n of FIDS . Installation of an ice det ection system is considered a safety enhancem ent since the icing conditions m a y be identified or confirm e d at an early stage and appropriate actions can be initiated in a tim e ly m a nner. However, recent investigations have shown that p r evious ly ce rtif ic ated ice detec tion sy stem s m a y not detect ai rfram e and engine icing in som e part 25, Appendix C conditions. It has b een dem onstrated in an icing wind tunnel that
atm o spheric m o isture m a y fail to freeze on ice d e tector prob es even thou gh ice m a y be accreting on other airplane surfaces in low freezing fract ion conditions. W ith the continuing developm ent of ice detection system s and due to recent in-servi ce in ciden t s, the FAA has dete rm ined there is a need to define specific criteria to ce r tif y ice de te ction sys t em s that are us ed as the so le m eans of determ ining when the ice protection sy stem s are activated. S ee AC 20-73A.

15AC 23.1419-2D 4/19/07

(d) Icing Conditions Outside of Part 25, Appendi x C. Ice detectors typically have lim itations with certain atm o spheric phenom ena, e .g. ice crystal conditions, outside of part 25, Appendix C, which the applicant m u st understand and not rely on the PFIDS to detect these conditions. There have been cas es (an anom aly that has affected som e engine m odels) where
atm o spheric ice c r ysta ls ingested in the initia l f a n stages of jet engines have m e lted, and re-accreted on subsequent low pressure com p ressor stages or initial stage s to the h i gh pressur e co mpressor resulting in engine core ice. Subs equent shedding of this type of ice acc r e tion ha s res u lted in at le ast one unrecoverable engine surge. Therefore, appli cants m u st be aware of the poten tia l lim itations of engines during ice crystal conditi ons without reliance on the ice de tection system . Current policy considers this potential condition in § 23.1093(b)(1)(ii) which requires dem onstration of adequate engine perform a nce in ice crystal conditions du ring falling or blowing snow. 14 CFR part 23 and part 33 regulations and com p liance m e thods intend to provide unrestricted engine operation throughout th e atmospheric environm ental envelope.

m. Fluid (Freez i ng Point Depressant) Systems. F r eezing point depr essant fluid system s have been s u ccessfully certificated on part 23 airplanes. However, th is type of system is not as common as other ice protection system s and that prom pted the FAA in 1986 to publish inform ation on certification of these system s in DOT/FAA/CT-TN86/11. Ce rtification highlights from this publication are repeated below.

(1) Analyses. The two critical analys es required ar e the fluid flow rate required and an evaluation of the operational a ngles of attack, w h ich will dictate chordwise coverage.

(2) Fluid Capacity. The fluid capacity does not have to exceed the m a xi m u m endurance of the airplane but the m i nim u m should be as follows in Table 1.

TABLE 1. FLUID CAPACITY

Airplane Type Minimum Fluid Capacity is the g reater o f:

Turbojet powered airplanes 90 m i nutes or 15 percent of the m a ximum endurance based on the f l ow rate required in continuous m a xi m u m icing conditions Turbopropeller airplanes with m a xi mum operating altitude above 30,000 feet

Turbopropeller airplanes with m a xi mum operating altitude 30,000 feet and below 150 m i nutes or 20 percent of the m a xim u m endurance based on the f l ow rate required in continuous m a xi m u m icing conditions Reciprocating engine powered airplanes

164/19/07 AC 23.1419-2D

(3) Fluid Quantity

.
(a) There should be a fluid quantity indicator to allow the crew to determ ine how much longer the fluid will last. The f l uid quan tity indicator sh ould be evaluated to d e term ine that it is p l a i nly visible to th e pilo t and that the indicator provided can be effectively read.

(b) If it is d e sire d that the air p lane be d i s p atched with less th an full fluid in the reservoir, the AFM should contain a chart or table to allow the crew to determ ine the m i ni m u m f l uid leve l. The AFM lim itations should state a m i ni m u m dispatch fluid level of 90 m i nutes based on the flow rate required in cont inuous m a xi m u m icing conditions.

(4) Fluid Characteristics.

(a) The freezing point dep r essant fluids used become a gel at very cold
tem p eratures and the temperature extrem es to which the airplane will be operated should be considered when evaluating th e res e r voir, pum p and plum bing installations.

(b) Certain fluids used in ice protection system s, such as the alcohol used in older propeller system s, are flammable. Com ponents of these system s must meet the flamm a ble fluid protection requirem e nts of § 23.863. No com ponents of these system s m a y be installed in
passenger or crew com p a r tm ents without th e protection required by § 23.853(d) (prior to

am endm ent 23-34) or § 23.853(e) (after am endm ent 23-34). An accessib l e shutoff should be provided in system s usi ng flammable fluids.

(c) The effect of fluid ingestion into engi nes, Auxiliary Power Units (APUs), and

accesso ries should be ev aluated. The com p atibility of the flu i d with eng i ne com pone nts should be exam ined to verify that adverse reaction s such as corrosion or contam ination do not occur, or are prevented through inspect ion or other m easures

(d) The effect of fluid com p atibility with electrical contacts and with airframe

com ponents, particularly com posite m a terials, sh ould be evaluated. The applicant should verify that adverse reactions such as corrosion or c ontam ination do not occur, or are prevented through inspection or other m easures (for example, if ethy lene glycol is a com pone nt fluid, then silver and silver-plated electrical switch c ontacts and term inals should be protected from contam ination by the ethylene glycol to avoid a fire hazard).

(e) There should be sufficient AFM and m a intenance m a nual wa rnings on handling fluids. AL5 is 85 per cent mono-ethylene glycol, w h ich is considered extrem ely toxic.

(f) Another freezing point depre ssant fluid, TKS80, is availa ble. Icing tunnel tests of TKS80 a nd AL5 fluids have shown that they pe rform differently. The fl uid reservoir should be placarded to perm it only the fluid(s) that have been tested during certification.

(g) To avoid co nfusion, the fluid filler ta nk cap should be disting u ishable from other caps s u ch as fuel and a placard stating a pproved fluid s hould be located near the filler cap.

17AC 23.1419-2D 4/19/07

(h) There should be adequate drainage in th e areas that hold or can receive spillage from leaks.

(5) Windshield Visibility. The effect of the fluid on windshield visibility should be evaluated to show com p liance to § 23.775(f) if either the windshie ld or propellers are protected with a freezing point depressant system. On m a ny of the approved inst allations the windshield system is turned off just prior to landing.

11. Flight Test Planning. When operating any airplane in an icing environm ent, degradation in perform a nce and flying qualities m a y be expected . The prim ary purposes for flight testing an airplane equipped for flight in ic ing conditions is to evaluate su ch degradation, determ ining that the flying qualities rem a in adequate, and that pe rform a nce levels are accep table f o r this f light environm ent. For airplanes w ith a certification basis of 23- 43 or higher, § 23.1419(a) requires that an airp lane com p ly with the perform a nce, stability, contr o llab ili ty and m a neuverability regulations of part 23, Subpart B. Flight testing in m easured, na tural icing conditions is required by § 23.1419(b) unless sim ilarity is used as th e m e thod of compliance. In addition, unless sim ilarity can be used, § 23.1419(b) requires at least tunnel testi ng, dry air testing, or airborne tanker tes tin g.

a. The flight tests and analys es of flight tests should:

(1) Evaluate norm al operation of the airplane with th e ice p r otec tion system installed in non-icing flight.

(2) Evaluate op eration of th e airp lane w ith an ticipated in-fligh t accum u latio ns of ice.

(3) Verify the analyses conducted to show adequacy of the ice protection system s throughout the icing envelope of part 25, Appendix C.

(4) Develop procedures and lim itations f o r th e use of the ice protection system in

norm a l, abnorm a l, and em ergency conditions.

b. Flight tests for a typical pa rt 23 airplane icing certifica tion are generally conducted in three s t ages:

(1) Initia l Dry Air Tests With Ice Protect ion Equipment Installed And Operating. Initial d r y air tes t s ar e us ually the f i rs t steps cond ucted to exte nd the bas i c airp lane ce rtif ication to evaluate the airp lane with the ice pro t ection sys t em installed and operating. The initial dry air
tests are con ducted to v e rify that the ice pro t ectio n system does not affect the flying qualities of the bas i c airplane in clear air. Dry air tes t s are us ed to: 1 ) verify proper ice protection system operation, 2) collect protected su rface tem p erature data to vali date therm a l analysis, and 3) evaluate the effect of increased electrical and/or bleed dem a nds on the engines and other installed system s.

184/19/07 AC 23.1419-2D
(2) Dry Air Tests With Predicted Simu lated Ice Sh apes Installed. Dry air tests with predicted, simulated critical ice shapes installe d are usually the second step for certification for flight in icing. Airplane perform a nce and ha ndlin g characteris tics are ev aluated with these sim u lated ic e shapes.

(a) Sim u lated ice on unprotected areas are t ypically determ ined by analysis codes.

(b) Sim u lated ice on protected areas is t ypically determ ined by a com b ination of analysis and em pirical data. Analyses are usua lly validated by ground tests such as icing tunnel tests where the design variables can be controlle d to som e extent, and the testing is m o re

econom ical, versus icing flight tests.

c. Flight Test Safety. FAA Order 4040.26A “Aircraft Certific ation Service Flight Safety Program ” should be cons ulted for flig ht tes t risk assessm ents and risk m itig ations. M a n y ice shape test flights, and stall testing with ice accr etions, are considered high risk. Many applicants have equipped their ice shape flight te st airplane with a stall/spin chute.

Flight Tests in Icing Conditions. Flight tests in icing condi tions, including artificial icing tests such as flight behi nd an airborne icing tanker airc raft, are norm ally e m ployed to dem onstrate that the ice protecti on system perform s under flight conditions as the analysis or ground test indicated. These dem o nstrations should be m a de at various points (targeting critical points) in the icing envelope of part 25, Appendix C, to verify th e airplan e ' s ability to s a f e ly operate throughout that icing envelope.

12. Flight Tests

. The f o llowing section s cover th e m a jor f light tests and/or analyses norm ally perform e d to substantiate the flight aspects of an ice pro t ectio n system :

a. Initia l Dry Air Tests with Ice Pro t ection Equipment Installed. Depending upon the detailed design of the ice protection system , som e prelim inary ground tests of the equipm ent m a y be warranted to verify the b a sic functio n of each ite m. Quantita tive da ta on such item s as tem p eratures of therm a l devices, fluid flow rates and flow pa tterns on liquid devices, or operating pressures of
pneum atic com ponents m a y be obtained as necessary to verify the system designs. The airplane should be shown to comply with the certification requirem e nts wh en all ice protection system

com ponents are installed and function i ng. This can norm a lly be accom p lished by perform i ng tests at those conditions found to be m o st critical to basic airplane aerodynam i cs, ice protection system design, and powerplant f unctions. .S everal comm only used ice protection system components are discussed below to illustrate typical flight test practices. Other types of equipm ent should be evaluated as their spec ific design dictates.

(1) Pneumatic Leading Edge Boots.

(a) O p erati on. Boot inflation rate and inflated boot shape are important param e ters in ice accretion rem oval. Tests should dem onstrate a rapid rise and decrease in operating pressures for effective ice rem oval. This press u re rise tim e , as well as the m a xi m u m operating pressure for each boot, should be evaluated throu ghout the al titude band o f part 25, Appendix C—Mean Sea

19AC 23.1419-2D 4/19/07
Level (MSL ) to 22,000 feet above MSL—unless perfor m a nce constraints or aircraft lim itations unrelated to the ice protection system in th e AFM restric t the airp la ne to a lesser altitude range.

(b) Minimum Operating Temperatu re. Boots should be operated in flight at the

m i ni m u m envelope tem p erature (-22 degrees Fahrenheit (F) of part 25, Appendix C, to dem onstrate adequate inflation/deflation and throughout the entire f light envelope. Boot s should be operated near the proposed AFM operating te mperature lim it, if below -22 de grees F, to demonstrate that no dam a ge occurs. The appropriate speed and tem p erature (if any) lim ita tion on activation of boots should be included in the AFM.

(c) Effect of In flated Boots. The operation of the boot s (inflation) should have no hazardous effect on airp lane performance and hand ling qualities. An example of an unacceptable hazardous effect is th at som e boot inflation sequencing schem e s re su lt in abnorm a l pitch attitude changes. If there are anom alous pitch changes in any configuration, appropriate inform ation or lim itation should be in the AFM. This can be sh own by inflating the boots at several speeds in the flight envelope from stall speed to (V NE + V D )/2 or (V MO + V D )/2 and observing the reaction of the airp lane. Th is test can b e hazardou s and should b e approach ed in a build-up m a nner by inflating the boots at increm ental airspeeds starting fr om the m i ddle of the flight envelope.

(d) Water Contamination. Consideration should be given to the potential for

accum u latio n of liquid water ins i de the pneum atic deicing b oots, which could freeze within th e system and prevent proper operation. The pneum atic and boot arrangem e nt should be exam ined for low points, which m a y collect water, and consid eration should be given to the installation of water drainage points. P e riod ic inspection and drainage proc edure instructions should be provided in the appropriate m a nual. Sim ilarly, placem ent of the pressu re sensor(s) sh ould be evaluated to prevent m i sleading boot inflation indications. An eval uation of the effectiveness of water/air separato rs and / or drainage holes should be accom p lished by flying through p r ecip itation followed by a verification of proper boot inflation at freezing altitudes.

(2) Electric Propeller Boo t s.

(a) Dry Air Function Flight Test.

1 . System Function. W h e n flying in dry air, the system s should be monitored to confirm pr oper function. It is sugg ested that system current, brush block voltage (between each input brush and the ground brush), a nd system duty-cycles be m onitored to assure that proper power is applied to the deicers.

2 . Temperatu re Measurements. If not furnished by the m a nufacturer, surface tem p eratu r e m easurem ents m a y be m a de dur ing dry air tests. These surface tem p erature

m easurem ents are u s eful for corre lating analytically predicted dry air tem p eratu r es with m easured
tem p eratures or as a gen e ral indicato r that th e sy s t em is functioning and th at each d e icer is heating.

204/19/07 AC 23.1419-2D

3 . Vibration. The system operation should be checked throughout the full certificated Revolutions Per Minut e (RPM) and propeller cyclic pi tch range expected during icing flights. Any significant vibra tions should be investigated.

(b) Maximum Temperatu re. Consideration should be given to the m a xi mum tem p eratures that a composite propeller blade m a y be subjected to when the deicers are energized

. It m a y be useful to m oni tor deicer bond-side te mperatures. When perform i ng this evaluation, the most critical conditions should be investigat ed. F o r exam ple, this m a y occur on the ground (propellers non-rotating) on a hot day with the sy stem inadvertently energized. Service difficulty reports have indicated propeller damage duri ng d e -ic e /an ti- ic e syst em activation during

m a intenance without the engines running.

(c) Precipitatio n . The system should be m onitore d to confirm pr oper function in precip itation

. There hav e been des i g n s that allow e d water to reach the electrical b r ush blocks and prevent their operation.

(3) Electric Windshield Anti-Ice.

(a) Thermal Analysis Validation. Dry air flight test s should be conducted in support of th e system s design, as requ ired. Inn e r and outer win d shield su rface tem p erature evaluations of the protected area m a y be needed to support therm a l analyses. Therm a l analysis should substantiate th at the surf ace temperature is sufficient to m a intain an ti-icing capability without causing structural dam a ge to the windshield. In the case of add-on plates, tem p eratures of the basic airplane windshield, inside and out, m a y also be needed, particularly with pressurized airplanes.

(b) Cockpit Vis i bility. An evaluation of the visibil ity, including distortion effects through the protected area at m a ximu m heat, should be m a de in both day and night operations to show com p liance to § 23.775(f).

(c) Si z e of Protected Area. The size an d location of the pro t ected area shou ld be reviewed for adequate visibility, especially for a circling approach and landing conditions. Crosswinds and runway light visi bility during instrum e nt landings need to be considered.

(4) Pitot and Static Pressure Sources. If the air data system configuration of either the pitot or the static source(s) differs from that of the basic airplane, then airspeed and altim e ter system calibrations should be evaluated for co m p l i ance with the certification requirements. A

com ponent surface tem p eratu r e evaluation m a y be n ecessary to verify therm a l analyses. Section 23.1325(b) requires that static pressu re port design or location shoul d be such that the correlation between air pressure in the static pressure system and true ambien t a t m o spheric s t a tic pressur e is not altered when the airplane encounters ic ing conditions. Section 23.1325(b)(3) allows antiicing m eans or an alternate source of static pre ssure m a y be used in showing com p liance with the requirem e nt.

21AC 23.1419-2D 4/19/07
(5) Stall Warn i ng and Angle-of-Attack Sensors. Ice could form on these sensors if these dev i ces are not p r o t ected. W h en the icing a pproval requires installati on of new or m odified sensors, that sensor' s functi on shou ld be evalua te d f o r com p liance with th e cer tif ica tio n requirem e nts. These sensors m a y not require heat for ice protection if substantiated by analyses. A surface temperature evaluation may be neces s a ry to verify therm a l analyses. Consideration should be given to ice form ations on the airfram e in the vicinity of the sensor m ounting location that m a y affect the sensor' s operation.

(6) Pitot Tube. Section 23.1323 requires a heated pito t tube or an equivalent m e ans of preventing m a lfunction due to icing for airplanes certificated for inst rum e nt flight rules or flight in icing conditions. S e ction 23.1326 requires a pito t tube heat indicating system if a flight instrum e nt pitot heati ng system is installed to comply with § 23.1323.

(7) Fluid (Freez i ng Point Depressant) Systems.

(a) Fluid Coverage. Dry air testing should include evaluation of fluid flow paths to determ ine that adequate and uniform fluid dist ribution over the protected surfaces is achieved. Colored fluid or colored water with cam e ra docum entation may be used. A range of angles of attack should be evaluated with both high and low volum e rates. Inlets or openings where fluid ingestion will have a detrim ental effect should be evaluated.

(b) Aircraft Performance. Dry air testing should also include perform a nce testing with the system operat ing sin ce drag increases hav e been docum e n ted on previous certification program s.

(c) Temperatu re. The system should be functiona lly tested at the m i ni m u m part 25, Appendix C a m bient tem p eratures.

(d) Windshield. The fluid anti-ice/deice sy stem s may be used to protect propellers and windshields, as well as leading edges of airfo ils. The fluid for windshield fluid system s, and for propeller fluid system s forw ard of the windshield, should be tested to dem onstrate that it does not beco m e opaque at low tem p erature.

(e) Cockpit Annunciations. Means of indicating fluid flow rates, quantity

rem a ining, and so forth, should be evaluated to dete rm ine that the indicators are plainly visible to the pilot and that the ind i cation s pr ovided can be effectively read.

(8) Compresso r Bleed Air Systems. T h e effect of any bleed air extraction on engine and airplane perform a nc e should be exam ined and shown in the AFM perfor m a nce data. The surface hea t distribution analys is sho u ld be verified for varying flight con d itions inc l u d ing clim b, cruise, ho ld, and descen t. A tem p erature ev al uation m a y be necessary to verif y the th erm a l analyses. If a m i ni m u m engine speed is required for ice protection system operation, the ability to perform nor m a l and e m e r gency descents should be ev aluated. If com p ressor bleed air is used for anti-icing an engine cowl that is m a de of com posite m a terial, a therm a l analysis/survey should be conducted to assure there is no engine cowl delam i nation or other structural failure.

224/19/07 AC 23.1419-2D

(9) Ice Inspection Light(s). Ice insp ection lights m a y be necess a ry if operations are dependent upon observing ice accumulations at ni ght (§ 23.1419(d)). Ice inspection lights should be evaluated both in and out of clouds during night flight to dete rm ine tha t adequa te illum ination of the com p onent of interest is available withou t excessi v e glare, reflectio ns or other distractions to the fligh t crew. These tests m a y be c onvenien tly accom p lished both in and out of clouds during dry air tests. Use of a hand-held flashl igh t for ice detection is not acceptable. As described in § 23.1419(d), “The Airp lane Flight Manual or other approved m a nual material m u st describ e the m eans of determ ining ice f o rm ati on and m u st contain inform a tion for the safe operation of the airplane in icing conditions.” A prim ary ice detection syst em m a y be certificated (see AC 20-73A for guidance), but such a system would require an Equivalent Level of Safety (ELOS) for section 23.1419(d) if an i ce inspection light is not installed.

b. Dry Air Tests w i th Simulated Ice S h apes.

(1) Why Do Simulated Ice Shape Flight Testing? The insta lla tion of sim u lated ice shapes allo ws airplan e perform a n ce and handlin g characteris tics to be evaluated in stable dry air conditions with the critical ice shape being held constant (no change of ice accretion due to erosion, shedding, and so forth, that can occur with natural ice shapes). Dr y air flight tests with sim u lated ice shapes installed al so result in a considerable re duction in the am ount of flight testing that would otherwise be requ ired to accu mula te the test ice shapes, and then evaluate their effects on airplane perform a nce and handli ng ch aracteristics in stab le a i r.

(2) Flight Test Safety. Dry air tests with sim u lated i ce shapes can be hazardous if not approached safely; therefore, the dry air flight test evaluation should be perform e d usi ng a buildup technique, considering increase s in spanwise coverage and dim e nsions of si m u lated ice shapes prior to f u ll span ice sh a p e tes t s.

(3) Simulated Ice Shapes.

(a) Critica l Ice Accretions. Consideration should be given to the type of ice protection system s (for exam ple: mechanical, fluid, therm a l, or hybr id), and the m o st adverse ice conditions (shape or shapes, texture, locati on, and thickness) for the relevant aerodynam ic characteristics for the following, as appropriate: delayed system turn on, intercycle ice, failure conditions, runback ice, and residu al ice. Consideration should also be given to unprotected areas. See paragraph 13b for m o re infor m ation. These predictive m e thods should be conservative and should address th e conditions associated with th e icing envelope of part 25, Appendix C, that are critical to the airplane' s perform a nce and hand ling qu alities in cr itical ph ases of the airplane' s operational enve lope, including clim b, cruise, des cent, holding pattern, approach, and landing. Ice shapes critical for perform a nce m a y not necessarily be critical for handling qualities. S ee AC 20-73A for m o re infor m a tion on determ ining critical ice shapes and corroboration of these ice shapes with natural icing flight te st ice accretions. See AIAA-2007- 1090, “Residual and Intercycle Ice on Lower Speed Aircraft with Pneumatic Boots” for m o re inform ation on critical ice shapes for pneum atic deicing boots.

23AC 23.1419-2D 4/19/07
(b) Ice Detectio n Systems. For aircraft that have an ice detection system

, consideration m u st be given to delays in ic e detection and annunciation. These delays m a y include slow ice detector res ponse at tem p eratures near free zing (low freezing fraction as discussed in AC 20-73A) and the number of pr obe heat cycles utilized for annunciation or
autom a tic ice protection activation.

(c) Engine and Cooling Inlets. If ice is expected to accum u late at the engine or cooling inlets during icing encounters, then test s should be perfor m ed with critical ice shapes, typically representing a 45 m i nute hold, installe d on these inle ts. Test s should consider the critica l oper a ting tem p eratures and altitud e s w ith in Appendix C icing cond itions. Gen e rator cooling tests should be perform e d wi th the m a ximum icing load on the electrical system

.
(4) Flight Test Object ives.

(a) Performance. The effect of the ice s h apes on stall speeds and airplane clim b perform a nce should be determ ined. Stall wa rning m a rgins and m a ne uvering capability should also be evaluated. Operating speeds, stall wa rning speeds, and AFM perfor m a nce infor m ation should be ad justed, if necessary, to p r ovide a ccep table p e rform a nce capability and stall warn ing

m a rgins. The com putation of the effects of ice on AFM perform a nce should include reductions in engine power or thrust resulting from the appli cable operating mode of th e ice pro t ec tio n system

.
(b) Handling Qualities. Handl i ng char act e ri sti c s ar e expected to degrade in icing conditions and should be investig ated to determ ine that the “a irplane is capable of operating safely.” For certification basis before am endm ent 23-43, subpart B requirem ents are used as guidelines. For certificati on basis at am endm ent 23-43 and higher, several subpart B requirem e nts also apply in icing conditions. This is addressed in paragraph 13a. The results of these tests may be used in preparing specific AF M operating procedures and lim itations for flight in icing conditions.

(c) Air Data Calibrations. If ice accretion is predicte d to alter the position error of the production air data system (e.g. radom e ice accretion )

, the position error would need to be determ ined using air data calibration flight test s (i.e. tower fly-by, trai ling cone, speed course) with the critical, s i m u lated ice shap es determ ined by analys is.

c. Flight Tests in Icing Conditions. Flight tests in m easured natural icing and the use of sim u lated icing tools such as ai rborne icing tankers and icing wind tunnels are norm a lly em ployed to dem onstrate that the ice prot ection system perfor m s under flight conditions as the analysis or other tests indicate. They are al so us ed to confirm the analys es used in developing the various

com ponents (for exam ple, ice detect ors) and ice shapes and, in the ca se of natural icing tests, to confirm the conclusions reached in flight test s co nducted with sim u lated ice shap es. Testing should be accom p lished at various points in the ic ing envelope of part 25, Appendix C, to verify the airplane' s ability to safely ope rate throughout that icing envelope.

244/19/07 AC 23.1419-2D
(1) Instrumentation. Sufficient instrum e ntation should be planned to allow docum entation of i m portant airplan e , system a nd com ponent param e ters, and icing co nditions encountered. The following para meters should be considered:

(a) Altitude, airspeed, and engine power.

(b) Temperatu res. Static air tem p erature, engi ne com ponent temperatures (for

exam ple, oil, heat exchanger fluids, cylinder head ), electrical generation equipm ent tem p eratures, surface tem p eratu r es, in terlam inate tem p eratures , and any other key temperatu r es th at could b e affected by ice protectio n equipm ent, by ice accu mulation or other key te mperatures that are necessary for validation of analyses.

(c) Liquid w a ter content can be m easured using a hot-wire based instrum e nt, calib rated drum , or other equivalent and acceptable m eans.

(d) Median volumetric dro p let diameter can be approxim a tely determ ined by using a drop snatcher to expose gelatin oil or s oot slide and then m easur ing the resultant im pact craters, or by use of m o re sophisticated equipm ent such as a laser based droplet m e a s uring and recording instrum e nt.

(e) Cameras and dimensional reference aids to assis t in de te rm ining ice accretion thickness and ice accretion coverage.

(2) Artificia l Ic ing.

(a) Why Do Ar tificial Icing Tests? Te sting in ar tif icia l ic ing e nvironm ents such as icing tunnels or behind airbor ne icing tankers represents one way to pre d ict the ic e protec tion capabilities of individual elem ents o f the ice pro t ection equip m ent. The high liquid water content and large drop size conditions of Appendix C are eas ily sim u lated and not frequently encountered in natu ral icing f light te sts. Due to th e us ually small dim e nsions of the artificial icing environm ent, testing is u s ually lim ited to secti ons of lifting su rfaces, to co mponents having sm all exposed surf aces such as heated p itot tubes, an ten n as, air inlets includ ing engine induction air inlets, em pennage, and o t her su rfaces having sm all lead ing ed ge radii and windshields.

(b) Airborne Icing Tankers. An artificial icing exposure m a y be obtained by the use of onboard spray nozzles forward of the com p onent under exam ination or by flying the test airplane in the cloud generated by an airborne icing tanker. Reco mmended procedures for airborne icing tanker testing, including in strum e ntation requirem e nts, are in SAE ARP 5904, “Airborne Icing Tankers.”

(c) Icing Tunnels. Icing tunnel tests have been accepted for definition of preactiv ation, intercy c le, residual, and runback i ce o n protected surfaces with the followin g consider atio ns:

25AC 23.1419-2D 4/19/07

1

. Scaling. A f u ll-sca l e tes t ar tic le is p r ef erable due to uncer tain ties in ic e accretion scaling. Refer to AC 20-73A for m o re inform ation on scaling test param e ters.

2

. Conformity

. The test article m u st be confor m e d. Although parts of the ice protection system m a y be si m u lated, critical system param e ters m u st be conform e d. An

exam ple would be deicing boot steady state pressu re, and pressure rise tim e and decay tim e.

3

. Tolerances. Ice protection system tolerances on the production airplane, such as boot operating pressure, m u st be accounted for.

4

. Operational Consideration. Proposed ice protection system operation (activation procedures, ice detection system delay, and deicing boot cycle tim e s) m u st be accounted f o r in the test m a trix.

5

. Spray Times. If the facility cannot p r oduce th e required LWC, spray tim es can be adjusted to provide the equivalent water catch for part 25, A ppendix C cloud lengths. If large ice s h apes or run b ack ice is expected, test am bient temperat ure m a y have to be adjusted to provide an equivalent freezi ng fractio n. Tem p eratures can change the ice adhesion/shed characteristics and this should be taken into acco unt when adjusting test param e ters. The test

m a trix should include su fficient tim e in continuo us m a xi m u m condition s to evaluate the stability and cyclic nature of intercycle and residual ice. Certain unique design featur es, such as stall s t rip s mounted on deicing boots, m a y not readily shed i ce and spray tim es up to 45 m i nutes need to be evaluated.

6

. Test Sectio n. An outboard wing section is usually tested since it is typically m o re critical for aerodyn amic degradations due to the re duced scale rela tive to the wing root (on win g s incorpo r a ting sign if ic ant tap e r r a ti os). It will also have h i g h er wate r co llec tion efficiency and m a y operate at a lower angle of attack, thereby prom oting greater aft impingem e nt of droplets o n the suction surface. For therm a l sy stem s, the outboard sections also rep r esent the
extrem ities of the bleed air sys t em where tem p erat ure and pr essure losse s are th e gre a tes t , which can be critical for runback accretions. The dist rib u tion of icin g cloud param e ters alon g the test span should be taken into account.

(3) Natural Icing.

(a) Why Do Flight Tests In Natural Icing Conditions? Section 23.1419(b) requires flight test in m easured natural icing co n d itions. F lig ht tes t s in n a tura l ic ing c onditions are necessary to dem onstrate the acc eptability of the airplan e and ice protection system for flight in icing conditions. AC 20-73A provides additi onal information that w ould be useful when estab lish i ng a natur a l ici ng flight test program

.
(b) What Icing Conditions Should Be Tested?

1

. Continuous Maximum Icing Conditions. At least one exposure to icing conditions within the part 25, Appendix C, continuous m a xi m u m e nvelope should be

264/19/07 AC 23.1419-2D

obtained. T h e exposure should be sufficiently stabilized to obtain valid data. It is often difficult to obtain temperature stabilizati on in brief exposures. Additiona l exposures m a y be required to allow extrap olation to th e envelope c r itica l c onditions by analysis. Te st data obtained during these exposures m a y be used to validate the analytical m e thods used and the results of any preced ing simulated icin g tests.

2

. Intermittent Maximu m Icing Conditions. Past experience has shown that f ligh t te sting in n a tu ral inte rm ittent m a xim u m icing con d itions m a y be hazardou s due to

accom p anying severe tu rbulence an d possible h a il en c ounters that m a y heat lo ads, critical shapes,

accum u latio n, and accu mulation rates, and so forth) are ad eq uate under these conditions, and sufficient ground or flight test data exists to ve rify the analysis, then hazardous flight testing should be avoided.

3. Number of Icing Encounters . There should be sufficient icing encounters to achieve all test plan objectives . The natural icing perform a nce and handling qualities m a trix in Table 3 of this AC consists of at least three encounters.

(c) How Much Ice Should Be Allow e d to Accrete? extensively dam a ge the test airplane. When design analyses show that the critical ice p r o t ection de sign points (that is,

1

. Normal Ice Protection System Operation. Sufficient data should be taken to allow correlation with dry air tests using sim u lated ice shapes. T h is should be

accom p lished with a targ et accreti on thickness eq uivalen t to the 45-m i nute dry air ice shapes on an unprotected part of the wing. Handling qua lities and perform a nce should be subjectively reviewed and determ ined to be in general correlation with those f ound in dry air testing. Refer to paragraph 13.a. for perform a nce, stability, control and m a neuverability requirem e nts.

2

. Delayed Ice Protectio n System Activation. In addition, flying qualities and performance should be qualitativ e ly evaluate d with the ice accum u lati ons existing just prior to operation of deice (as opposed to anti-ice) com ponents. The ice protection system s are to be activ ated by the flight crew in accordance with app r oved AFM procedures when icing conditions exist; however, for anti-ice com pone nts, tests should be conducted that simu late inadvertent icing encounters in which the pilot m a y not recognize th at the airplane is a bout to enter an icing condition an d the anti-ice com ponent m a y not be activ ated un til actual ice build-up is noticed. A delayed ice accum u latio n event of 30 seconds to tw o m i nutes has been u s ed in th ese tests to sim u late the flight crew' s fa ilure to recognize an icing condi tion. For engine ice protection system s, which for aft fuselage m ounted engi nes can include the inboa rd wing ice protection system , a delay of two minutes is utilized to validate the ice shedding analyses and § 33.77 ice slab test results. For the delayed ice accum u latio n tim e event, consideration should be given to the ic ing co nditions ; th e icing recog n ition m eans available, recomm ende d crew procedures, and ice protection system perfor m a nce of the particular aircraft. T h e tes t s to b e accom p lished are summarized in Table 3 of pa ragraph 13c of this AC.

27AC 23.1419-2D 4/19/07
(d) What Should Be Evaluated During Natural Icing Tests? All system s and

com ponents of the basic airplane should continue to function as intended when operating in an icing environm ent. Some considerations are:

1

. Engine operation and equipment operation such as oil cooling and generator cooling under m a xi m u m load should be m onitored during icing tests and be f ound acceptable f o r this op eration If data is analy zed in accordan ce with § 23. 1043, the temperatures need to be corrected only to 32 degrees F, not a hot day. Natural icing f light tests should include evaluation of ice protection system s with bleed air from engines when th e thro ttle is at the f l ight idle s t op. Refer to AC 20-147 for addition a l guid a nce for turb ojet eng i nes.

2

. Engine alternate induction air sources should rem a in functional in an icing env i ro nm ent.

3

. Fuel system venting sho u ld not be af fected by ice accum u lation.

4

. Retractable landing gear should be available for landing following an icing en cou n ter. Gear retraction sh ould not res u lt in an uns afe indicatio n b ecause of ice accretio n.

5

. Ice sheddin g from components including ante nnas and propellers should

cause no m o re than cosmetic dam a ge to other pa rts of the airplane, including aft-m ounted engines and propellers. If flight testing is used to validate shedding trajectories, there should be dedicated test points to evaluate shedding. Examples would be flying in warm er temperatures to facilitate ice shedding, and evaluating various opera tional angles of attack and sideslip.

6

. Stall Warning and Maneuver Margin. W ith ice accretion s on the airplane, acceptable stall warn ing (aerodynam i c or artificial) a nd stall protection, if a stall protection system is installed, s hould be provided to vali date the results of the dry air ice shape testing. The stall warning should m e et the require m e nts of § 23.207(a), (b), and (c). The type of stall warning in icing cond itions should be the sam e as in no ic ing conditions. Biasing of the stall warning and stall protection system , i.e. resetting tr igger points to lower angles of attack when ice protection is initiated, may be necessary to ac hieve required m a neuver ma rgins to stall. The

m a neuver margin requirem e nts § 23.207(d) should be dem ons trated in icing conditions. The stall warning m a rgin should be evaluated with various ice accretions as summ a r ized in Table 3. See paragraph 13.c.

NOTE 1: This test and any stall or handling qualities tests should be

accom p lished in daytim e visual m e teorologi cal conditions, after accreting ice, for safety. .

7. Performance, Stability, Controllability. See paragraph 13.c.

8

. Ice detectio n cues or ice detection system operation tha t th e pilo t re lies on for tim ely operation of ice protection equipment should be evaluated in all anticipated flight conditions, including night.

284/19/07 AC 23.1419-2D

9

. Ice inspection lights should be evaluated in natural icing and night conditions to verify that they illum i nate ice build -up areas, are adequate u nder the con d itions encountered, and do not introduce ob jectionable glare. Evaluate the cabin defogging system' s capability to clear side w i ndows for observation o f boot ice protection sys t em operation and ice

accum u latio n. If a defogging system is not pro v ided, the w i ndows should be easily cleared by the pilot without adversely in creas ing pilot worklo ad

.

10

. Flight Control Systems. Prim ary and secondary flight control surfaces should rem a in operational after e xposure to icing conditions. Ev aluations should confirm that aerodynam i c balance su rfaces are no t subject to ici ng th rough out the airp lane' s operating envelope (weight, Center Of Gravity (CG), an d speed), or that any ice accum u latio n on these s u rfaces does not interfere with or lim it actu a tion o f the contro l for these su rfaces inclu d ing re trac tion of flaps, slats and/or landing gear for a safe go around from the landing configuration.

11

. Air Data Systems. Ice accretions on pitot p r obes, static sou r ces, tem p erature probes, angle of attack and stall wa rning sensors

, and accretions forward of these sensors such as accretions on radom e s or other probes should be eval uated to determ ine the effect, if any, on the position error of the aircraft’s prod uction air data system and proper operation of stall warning or stall protection system s.

12

. Autopilot. All autopilot m odes should be evaluated in natural icing conditions to validate the dry air ice shape test results. All autopilo t m ode s should function properly in icing conditions. Airfram e leading edge ice accretions could a ffect control power and control hinge m o ments resulting in incorrect au topilot g a ins. Thes e evaluations should also show that au topilo t actu a tors function p r op erly and do not freeze u p. The auto pilot shou ld be engaged for an extended period of tim e in natural ici ng conditions to check for unusual trimm i ng and potential for ice to accrete in cont rol surface gaps and jam controls. ”

13. Vibration and Buffet. Should be evaluated, in cluding propelle r vibration.

14 . Pilot Workload. The workload in icing c onditions should be evaluated when showing com p liance to § 23.1523. Ice de tection, ice protection system operation and monitoring, and autopilo t operation and m onitoring (includi ng periodic disconnects), as a

m i ni m u m should be evaluated.

15. Documentation of Ice Accretions. Ice accum u l a tion on unprotected and protected areas, and behind protected areas, sh ould be observed and docum ented. Rem o tely located cameras either o n the test airplane or on a chase airplane have been used to docum e nt ice

accum u latio ns on areas that canno t b e seen from the test airplane' s flight deck or cab i n. Visual devices such as rods and/or paint stripes m a y be used to aid in vi sual dim e nsional analysis of ice accretions. Care should be taken sin ce som e m e as uring dev i ces m a y accrete ice and alter analysis of accretion s on a surface of im por tance. Surfaces m a y be painted a dark color s i nce rim e and

m i xed ice accretions m a y be difficult to see on wh ite su rfaces . The edges of paint strip e s can be efficient ice collectors if not sm oothed and m u st be accounted for. The location of all external

29AC 23.1419-2D 4/19/07

instrum e ntation installed for icing flight tests, including cam eras and visu al devices, should be analyzed to verify that ice-sh edding hazards are not introduced.

13. Performanc e and Handling Qualit ies. Airplane perform a nc e and handling qualities are degraded by ice accum u l a tions in various ways depending upon type, shape, size, and location of these accumulations. If num e rous unprotected areas exist, the wei ght and center of gravity effects of the ice form ations should also be evaluated.

a. Flight Tests

(1) Section 23.1419 at Amendment 23-43 or Later. In acco rdance with § 2 3.1419(a), "capable of operating safely" m eans that airplane perform a nc e, controlla bility, m a neuverability, and stability m a y be degraded from the non-ic ed airplane but must not be less than the requirem e nts in part 23, subpart B. Guidance for each subp art B regu lation, as related to icing, is in Appendix 6 of this AC. Unless noted otherwis e, the gu ida n ce is app lic able to all airplane categories f o r which compliance to § 23.1419 is being shown.

(a) Configurations and Flight Conditions. The handling qualities test m a trix for ice shapes can be reduced from the basic (no ice) m a trix, with concurrence from the adm i nistrator, to configurations and flight conditions that were deem ed critical based on th e no ice testing (basic aircraft certification). It is not required to test flight conditio ns at altitudes above the part 25, Appendix C icing envelopes.

(b) Harmoniz ation. The FAA and the European Aviation Safety Agency (EASA) are harm oni zing the perform a nce and handling qu alities requirem ents of part 25. This harm onization projec t will s t anda rdize the pe rf or

m a nce and handling qua lities requ ire m ents, and provide additional guidance m a terial for certification of part 25/large airplane s to saf e ly opera te in the icing conditions of part 25 /CS-25, Appendix C. Much of this perform a nce and handling qualities guidance has been adopted f o r part 23 airplanes and is pr esented in Appendix 6 of this AC. There have been som e m odifications for part 23 applications. For exam ple perform ance criteria had to reflect d i fferent catego r ies of airplanes (comm u ter category, norm a l category below 6,000 lb. m a xim u m weight, and norm a l category a bove 6,000 lb. m a xim u m weight). Also, stall speed to lerance criteria in som e cases were m odi fied to reflect lower stall speeds of part 23 airp lanes co mpared to transport airp lanes.

(c) Stall Speed. Section 23.1419, am endm ent 23-43, requires “...airplane perform a nce...m u st not be less th an that required in part 23, subpart B.” The stall speed requirem e nts of § 23.49 are included in subpart B perfor m a nce. Fo r part 23 aircraft that do not

m eet the emergency landing requirem ents of § 23.562(d), the stall speed at m a xi m u m weight must not exceed 61 knots. Recent flight testing o f deicing bo ot-equ ipped aircraft with sim u lated inte rcycle/r e s idual ice ha s shown stall lif t co ef f i ci ent losses of 17 percent to 23 percent with flaps extended. T h ese lift loss es were exp e rien ced on an airplane equipped with a stick pusher and on an airplane whose stall was de fined by aerodynam i c wing stall. Th is can represent a significant perform a nce penalty for new aircraft if they ha d to be designed to m eet the 61-knot stall speed requirem e nt with ice on protected su rfaces. Recently certific ated s i ngle engine part 2 3 airp lanes

304/19/07 AC 23.1419-2D

would m o st likely not meet this r e qu irem ent sinc e their no- ic e sta ll spe e d in land ing c onf iguration is at or near 61 knots. Perform a nce penalties would be large. As an example, calculations for one

recen tly certificated sing le engin e airplanes show that us eful load in ic ing would have to be reduced by 40 percent in order to m eet the 61- knot stall speed requi rement with no m a jor redesign.

In the notice of proposed rulem a king pub lished in the “Federal Register” on October 3, 1990 (55 FR 40598), for the proposed ru le that was to becom e am endment 23-43, the FAA stated the background for im pos ing subpart B requirem e nts on part 23 airplanes versus part 25 transport airplanes: “The just ification given was that normal and transport category airplanes must operate in about the sam e icing environm ent, but the norm a l category ai rplane is m o re likely
to rem a in in icing cond itions for longer periods of tim e because it m a y not have the perfor m ance capability to exit the ic in g environm ent as re ad ily as tran sport catego r y air p lanes.” No rm al category airplane airfoils, being sm aller than those of transpo r t airplanes, are m u ch more efficient collectors of ice and thei r percentage drag increase in icing co nditions are larger than transport airplanes. T h e requirement to m eet subpart B perfor m ance was added to guarantee there would be a given level of excess power that could be used to exit icing c onditions. An increase in stall speed in icing would not prevent an airpla ne from m eeting the subpart B perform a nce requirem e nts if it was accounted for in analyses and testing.

For airplanes that do not m eet the 61-knot stall speed re quirem ent with critical ice accretions, the applicant should consider the fo llo w ing com p e n sating features to p r op ose an

exem ption to the stall speed re quirem ent of § 23.1419(a), am endm ent 23-43. The exemption with the following com p ensating features would not advers ely affect safety since it is saf e r to m a ke a forced landing at higher speed than it is to in adve rten tly s t all the airplane. There have been m a ny f a tal acc iden ts in icing c onditions attributed to th e latter.

1. The airp lane with no ice accreti ons m eets the 61-k not stall sp eed requirem e nt of § 23.49(c);

2. The airplane with critical ice accretions as define d in paragraph 13b of this AC com p lies with the stall warning requirem e nts of § 23.207.

(aa) For airc raf t with ar tif icial stall wa rn ing system s, paragr aph 1 3 a (1)2 , m a y require a bias in the stal l warning schedules (resetting tri gger points to lower angles of
atta ck when ice pro t ec tio n is initiated ) to m a intain adequate stall warn ing m a rgins.

(bb) For aircraft without artif icial stall warning system s, 12a (1)(c)2

, m a y require one to be installed to m eet m i ni m u m stall warnin g m a rgin req u irem ents. Meeting § 23.207(d) m a y require an increase in operational speeds in icing to preclude nuisance stall warnings.

3. The AFM perform a nce data in icing conditions reflects the higher stall and operating speeds.

31AC 23.1419-2D 4/19/07

4. Most im portantly, the airplane with critica l ic e accretions has acceptable stall characteristics and is safe ly controllable with norm a l p iloting skill as required by §§ 23.201 and 23.203.

5. The tire requirem ents of § 23.733 and brake requirem ents of § 23.735 are

m e t with the higher s t al l and operating speeds.

6. The ground handling requirem ents of §§ 23.231, 23.233 and 23.235 and nose/tail wheel steering system of § 23.745, if applicable, are m e t w ith the higher landing speeds.

7. All other airplane system or testi ng requirem e nts that could be affected by higher operating speeds, such as autopilo t and flight director gains are evaluated.

8. Each seat/restraint system would have to include a safety belt and shoulder harness with a m e tal to m e t a l latc hing device (this would address STCs on older airplanes that do not include § 23.785 in their certification basis).

9. The airplane certification basis would have to include § 23.1091 at

am endm ent 23-51 and § 23.1093 at am endment 23-51 to provide the latest regulations for engine operation in icing conditions.

10. The airplane certification basis would have to include § 23.995 at

am endm ent 23-29. This regulation w a s prom ulga ted as a result of a National Transportation Safety Board (NTSB) recommendation and a 1983 study, which indicated at least half of off fie l d forced landings were a result of fuel m i s m anage m ent.

The above approach represents only the m i ni m u m consideration, other issues m a y have to be considered depending on the aircra ft design. In the petition for exem ption, the applicant needs to state why it would be in the public interest and include the weight penalty in icing conditions as a resu lt of com p lying with the 61- knot stall speed regulation.

(2) Section 23.1419 at Amendment 23-14. The definition of “capable of operating safely” is not defined in the regulation. The te sts and pass/fail criteria of paragraph 13a (1) should be used as a guide to develop a test program that de monstrates the airplane is capable of operating safely in the part 25, Appendix C, ic ing envelope. The regul ations italicized in Appendix 6 of this AC are not typically addr essed in showing com p liance to § 23.1419 at

am endm ent 23-14.

b. Ice Accretions.

(1) Airframe Ice Accretions.

(a) Definition of Ice Accretions. The most critical i ce accretion s in term s of handling ch aracteristics and/or perform a nce for each flight ph ase should b e determ ined. The

324/19/07 AC 23.1419-2D

param e ters to be considered are the flight cond itio ns (e.g., airp lane configu r ation, airsp eed, angle of attack. altitude) and the ic ing conditions of part 25, Appendix C (tem perature, liquid water content, m ean effective d r op diam eter). Table 2, parts I and II summarize the ice accretions for each flight p h ase for norm a l i ce protection system operation.

33AC 23.1419-2D 4/19/07

TABLE 2. I C E AC CRE TION DEFI NITIONS, P A RT 1 o f 2

Ice Accretion Norm al, Utility and Acro batic Categories or Turbojet Airplane with a takeoff configuration that includes leading edge high lift devices Commuter Category or Turbojet Airplanes w ith a takeoff configuration that does not include leading edge high lif t devices

Takeoff None if the AFM prohibits takeoff with any ice, snow and frost on the wing and control surfaces. Ot herw ise, “polished” f r ost, as per m itted by the parts 91 an d 135 operating rules should be defined by the applicant, show that procedures are practical (pilo t can d e term ine when it is accep tably polish e d ) , and sim u lated for flight test evaluation if not prohibited for takeoff in the AFM. Ice accretio n occurring between liftoff and 400 feet above the takeoff surfac e,

assum i ng accretion starts at liftoff in the “takeoff m a xim u m ici ng’ conditions, on:

• unprotected surfaces; an d

• the pro t ected surfaces appropriate to norm a l IPS operation; or

• the pro t ected surfaces if IPS operation is prohibited for takeoff. (It should be assum e d no flight crew action to activate the ice protec tion w ill o ccur un til at leas t 400 feet above the ground level, or higher if specified in the AFM.)

“Takeoff m a xim u m icing” conditions defined as:

• cloud liquid water content of 0.35 g/m 3 ;

• cloud droplets Mean Effective Diam eter (MED) of 20 m i crons; and am bient air tem p erature at ground level of m i nus nine degrees Centigrade (C)

This ice accretion m a y be sim u lated by 100 grit sandpaper on the leading edge, unless another roughness is substantiated.

344/19/07 AC 23.1419-2D

TABLE 2. I C E ACCRETION DEFI NITI ONS, PART 1 of 2 (Continued)

Ice Accretion Norm al, Utility and Acro batic Categories or Turbojet Airplane with a takeoff configuration that includes leading edge high lift devices Commuter Category or Turbojet Airplanes w ith a takeoff configuration that does not include leading edge high lif t devices
Also the following ice accretions should be addressed:

• Takeoff ice accretions defined under Normal, Utility an d Acrobatic Categories, if required.

• If a turbojet airplane without wing leading edge high lift devices,
contam ination sim u lated by 40- grit sandpaper on wing leading edges and the entire upper wing surface should be flight tested unless the AFM requires a pretakeoff visual and tactile inspection of the wing leading edge and up per surface, and any other surface deem ed critica l , in ground icing conditions.

35AC 23.1419-2D 4/19/07

TABLE 2. I C E AC CRE TION DEFI NITIONS, P A RT 2 o f 2

Ice Accretion Norm al, Utility and Acro batic Categories or Turbojet Airplane with a takeoff configuration that includes leading edge high lift devices Commuter Category or Turbojet Airplanes w ith a takeoff configuration that does not include leading edge high lif t devices

Final Takeoff Not applicable. Sam e as “takeoff” ice except ice accretion occurs between liftoff and 1,500 feet above the takeoff surface.

Enroute Ice accretio n on the unp rotected su rf aces, and an y ice accretion on the protected surfaces app r opriate to n o rm al ice protect ion system operation, during th e en route phase, in part 25, Appendix C, continuous or interm ittent m a xim u m icing conditions. Holding Ice accretio n on the unp rotected su rf aces, and an y ice accretion on the protected surfaces app r opriate to n o rm al ice prot ection system operation, during a 4 5 -m inute hold in part 25, Appendix C, continu ous m a xi m u m icing con d itions. Approach And Landing Ice accretion on unprotected surfaces sam e as “Holding” ice, and ice accreted on protected su rfaces appro p riate to no rm al system operation du ring an app r oach and landing. U pper surface im pinge m e nt due to reduced angle of attack with flap extension, ice on flap leading edge, and ice on leading devices when extended need to be addressed. R unback ice has been observed to develop on leading edge slats on some designs w h en extended, but not when retracted. Duration of approach ph ase is tim e to accrete 0.5 in ches of ice on unprotected part of wing with highest collection efficiency. Dura tion of landing phase is tim e to accrete 0.25 inches of ice on unprotected part of wing with highest collection efficiency.

PreActivation The ice accretion p r ior to norm a l system operation is the ice accretion form ed on the unprotected and norm a lly protected surf aces prior to activa tion and effective operation of any ice protection system in continuous m a xi m u m atm o sphe ric icing conditions. Ice detection procedures, ice detector system design and perfor m ance, and operating procedures (e .g., boot activation, fluid syst em flow rate) should be considered. Intercycle See Appendix 1 of this AC fo r definition. For airspeeds below 160 KCAS,

em pirical data should substantiate that de icing system s shed ice at each cycle.

Residual See Appendix 1 of this AC for definition.

Runback See Appendix 1 of this AC for defin ition. This ice type is frequently a byproduct of partially evaporative (running wet) i ce protection system s and therm a l deicing system s, but can also occur on deicing boots at a sm all tem p e r ature band near freezing. E m pirical data should be obtai ned at the following conditions, as a

m i ni m u m, at the LWC values within part 25, Appendix C:

a. outside air tem p eratures of 24 degrees to 28 degrees F;

364/19/07 AC 23.1419-2D

TABLE 2. I C E ACCRETION DEFI NITI ONS, PART 2 of 2 (Continued)

Ice Accretion Norm al, Utility and Acro batic Categories or Turbojet Airplane with a takeoff configuration that includes leading edge high lift devices Commuter Category or Turbojet Airplanes w ith a takeoff configuration that does not include leading edge high lif t devices

Runback

(Cont.) b. total air tem p eratures of 24 degrees to 35.5 degrees F;

c. tim e required to transit a c ontinuous m a xi m u m cloud of up to 55 nm

, correcting liquid water conten t for h o rizon t al ex tent.
Critical The ice accretion, applicable to the phase of flight that has the m o st adverse effect on perform a nce and flying qualities. For protected surfaces, intercycle ice, residual ice, and runback ice should be accounted for. Pre-activation ice should be accounted f o r if the AFM requires the flight crew to wait for a specified am ount of ice ac cre tion prior to ac tivation the ic e prot ection system s, or for system s, such as fluid system s, in which s y stem effectivene ss m a y take several m i nutes. In order to reduce the n u m b er of ice accretions to be considered when demonstrating

com p liance: (1) The m o re critical of takeoff ice a nd final takeoff ice m a y be used throughout the tak e off phase. (2) Holding ice m a y be used for the en route, holding, approach, landing, and goaround fligh t phases if it can be substantia ted to b e m o re critical than the ice accretions in those phases. (3) Holding ice m a y also be used for the takeoff phase provided it can be substantiated to be m o re critical th an takeoff ice and final takeoff ice. (4) The ice accretion th at has the most adverse effect on handling characteristics

m a y be used for clim b perform a nce tests provided any difference in clim b perform a nce is conservatively taken into account. (5) In som e instan ces th e shapes determ in ed in the various flight phases and flight conditions m a y be “enveloped” into one critical shape.

(b) Shape and Texture of Simulated Ice. The shape and texture of the sim u lated ice should be developed, and substantiated by agr eed m e thods. The ice shapes should be agreed to by the FAA prior to ice shape flight testing.

1. Common practices for deve loping ice shapes include:

(aa) Use of com p uter cod e s;

(bb) Flight in m e asured na tur a l ic ing con d itions ;

37AC 23.1419-2D 4/19/07
(cc) Icing wind tunnel tests; and

(dd) Flight in a controlled artifici al icing cloud (e.g. airborne icing tanker).

2. The ice accretion resulting from th e largest drops possible in Appendix C icing conditions should be considered for critic al ice shapes. A Langm u ir D drop distribution, 40
μm m e dian drop diam eter, continuous m a xi m u m ic ing conditions, should be considered. See A C 20-73A.

3. Natural icin g or airbo r n e tanke r tes t ing m a y show ice sh apes or accretion locations more critical than those s imulated. Ice shape testing of critical test points would then need to be re-flown with these m o re critical shap es.

(c) Ice Adhesion Inhibitors. For the determ ination or validation of intercycle and residual ice shapes and roughness on deicing boots, the application of any ice adhesion inhibitor such as ICE X is not per m itted f o r natura l ic ing f light tes t s, a r tif ic ial ic in g f light te sts or ic ing tun n el tests. Th is is because th e use of ICEX cannot be contro lled in operations and the effectiveness in operations degrades over tim e. (Intercycle ice is the ice accretion that exis ts on a de icing system surface jus t prior to an actuati on of the deicing s y stem ; resid u al ice is the accretion rem a ining imm e diately after an actuation.) Other products th at enhance appearance or life should also not be applied. Deicing boots can be clea ned at the start of a natural ici ng o r ar tif icia l ic ing test program per recommended m a intenance procedures.

(2) Propeller Icing. To date, clim b perform a nce analyses and climb flight testing with ice shapes have not taken into account propelle r efficiency lo sses due to ice accretion on the propeller blades. Deicing boot m a nufacturer’s analyses show that intercycle ice does exist with propeller deicing systems and their analyses do no t account for ice runback. The outer part of the blade, which norm a lly is not protected, theoretically has sufficient centrifugal force to shed ice. Stop fram e video of recent flight testing of a part 23 aircraft in Super-Cooled Large Drop (SLD) conditions have shown ice accretions on the full sp an of the propeller blades. Although this condition was outside of part 25, Ap pendix C icing conditions, there is a possibility that this m a y occur within som e portions of part 25, Appendix C.

(a) Airplane perfor m ance in icing conditions should include the propeller efficiency losses caused by propeller in tercy c le ice. This m a y be accom p lished by analys is.

(b) Propeller efficiency loss s hould be at least 10 percent to account for runback ice and intercycle ice, unless data substantiates another am ount.

(c) Airplane perfor m ance during natural icing flight testing should be quantitatively

com p ared with perform a nce during ice shap e flight tests. On reciprocating and turboprop powered airplanes, if there is de gradation in perform a nce com p ared to

384/19/07 AC 23.1419-2D
the ice shap e results, propeller efficien cy losses due to pr ope lle r ice acc re tions should be investigated.

(3) Failure Ice Accretions. Flight tests with f a ilur e ice shapes representing failures not shown to be extrem ely improbable should be conduc ted to validate hazard classifications and to develop procedures for safe operation following a failure. For exam ple, this testing m a y show that landing flap settings m a y have to be reduced following failure of the empennage ice protection system

.
(a) Failure ice accretion is defined as:

1

. “Holding” ice as defined in Ta ble 2 for unprotected surfaces; and

2

. For protected surfaces, o n e-half the accretion specified for un protected surfaces (22. 5 m i nutes) if the associated AFM opera ting procedure requ ires the airplan e to le ave the icing conditions as soon as possible, unless another value is agreed to by the responsible aircraft certification office.

3. For failure conditions that are: (a) no t annunciated to the flight crew, or (b) annunciated to the flight crew, but the associated AFM procedur e does not require exiting the icing conditions, the guidance in this AC for a norm al (i.e., non- f a ilur e ) c ondition is a pplicab le with the f a ilure ic e acc re tion

(b) If the failure is annunciated, and the AFM procedure requires exiting icing conditions, the applicant m a y propos e an ice accretion based on a realis tic exit scenario in lieu of the 22.5 m i nutes ice accretion. This failure s cenario should account for the tim e it takes:

1

. For the system to annunciate the failure (e.g., one deicing boot cycle);

2

. For the pilot to decide on a course of action and notify Air T r affic Control (AT C ) (e.g., two m i nutes); and

3

. To exit the icing conditions.

(c) The tim e to exit should include a 180-deg ree standard rate turn and transiting a 17.4-nautical m ile, part 25, Appendix C continuo us m a xi m u m cloud. Besides the design standard 17.4 nautical m ile horizontal cloud extent, a cloud ex tent of 46-nautical m iles (adjusted for liquid water content per part 25, Appendix C), which is expected for 10 percen t of icing encounters, should also be considered in the safety analysis . The exit scenario sha ll include the possibility that the airplane m a y have to clim b 4,000 feet out of icing if it results in a longer tim e than traversing the part 25, A ppendix C cloud.

c. Natural Icing Flight Tests. W h ether the perform a nce and handling qualities flight testing has b een perf ormed with sim u lated ice sh apes or in n a tura l ic ing c onditions, a ddition a l lim ited f ligh t tes ting de s c ribed in th is section sh ould be conducted in natural icing conditions.

39AC 23.1419-2D 4/19/07

W h ere f light testing with sim u lated ic e shapes is the prim ary m eans for showing com p liance , the objective of the tests described in this section is to corroborate the handling characteristics and perform a nce results obtained in fli ght testing with sim u lated ic e shapes. I t is acc eptab l e f o r som e ice to be shed during the testing due to air loads or wing flexure, etc., or during transit to a higher altitude o r test area for safety reasons. However, an attem p t should be m a de to accom p lish the
test m a neuvers as soon as possible after exiti ng the icing cloud to m i ni m i ze the atm o spheric influences on ice shedding. During any of the maneuvers specified in Table 3, the perform a nce and behavior of the airplane should be consistent with that obtained with simulated ice shapes. There should be no unusual control responses or uncommanded airp lane motions. Addition a lly, during the level turns and bank- to-bank rolls, there should be no buffeting or stall warning.

TABLE 3. NATURAL ICING PER F ORMANC E AND HANDLING QUALITIES T E STS

Configuration Ice Accretion Trim Speed Maneuver

Flaps up,
gear up Equivalent to 45-m i nute hold at critica l conditions. M i n i mu m Holding • Level, 40-degree banked turns;

• Bank-to-bank rapid ro lls, 30 degrees – 30 degrees;

• Clim b or level perform a nce evaluation;

• Autopilot te sts

• Straigh t stall (1 knot/s ec. deceleratio n rate, wings level, power off)

Landing flaps, gear down Tim e to accrete 0.75 inches on unprotected part of wing with highest colle ction efficiency V REF • Level, 40-degree banked turns;

• Bank-to-bank rapid ro lls, 30 degrees – 30 degrees;

• Clim b or level perform a nce evaluation;

• Straigh t stall (1 knot/s ec. deceleratio n rate, wings level, power off).

Flaps up,
gear up Defined preactiv ation ic e Optional • Level, 40-degree banked turns;

• Bank-to-bank rapid ro lls, 30 degrees – 30 degrees;

• Clim b or level perform a nce evaluation;

• Autopilot te sts

• Straigh t stall (1 knot/s ec. deceleratio n rate, wings level, power off).

d. Control System and Stall Protection System Tolerances. The sam e airplane and system production tolerances used in the non- icing tests should be used when evaluating perform a nce and handling qualities w ith ice accretions. Ice protection system production tolerances should be addressed du ring flight testing in natural icing conditions. Exam ples are provided in Table 4. Stall spee d and warning system tolerance are critic al when establishing tolerances f o r productio n acceptance flights.

404/19/07 AC 23.1419-2D

TABLE 4. FLIGHT TEST TOLERANCES

T e s t T o l e r a n c e s

Stall sp eed • Elevato r to m i ni m u m trailing e dge up if stall defined by aft control stop

• Stick pusher, if equipped, set for m i nimum angle of attack

• Flap travels should be set to m i nim u m allowable settings
Stall wa rnin g • Set f o r m a ximum angle of attack (m inim um m a rgin).

Stall chara c teris tic s • Elevator to m a xi m u m trailing edge up.

• Stick pusher, if equipped, set for m a xim u m angle of attack

Maneuver m a rgin • Stall warning set for m i nim u m angle of attack.

Natural icin g f light te sts • Pneum a tic boots set for m i ni m u m pressure

• Electrotherm a l system s set at m i nimum current

e. ICTS. To remove the risk of contam i n ated tailp lane stall from the operating envelope of the airplane, the applicant should demonstrate by test s or a com b ination of an alyses and tests, that the airplan e is safely con t rollable an d m a neuverable during al l phases of flight.

(1) Background . See Appendix 7 of this AC.

(2) Evaluation of Susceptibility to IC TS by Flight Test

(a) Longitudinal control and susceptibility to ICTS should be evaluated during the f o llowing f l ight tes t s with critica l ice shapes ins t a lled :

1. Flap extensions

2. Recovery from stalls

3. Level flight acceleration s

4. Longitudinal control tests required by 14 CFR 23.145.

(b) Susceptibility to ICTS should also be evaluated by conducting the zero-g pushover maneuver and steady heading sideslip.

1. Configuration

.
(aa) All com b inations of wing flaps a nd landing gear should be tested beginning w ith zero flaps up to the m a xi m u m flap setting to be approved for landing following an icing en cou n ter. Sin ce increas ed f l a

p extens ion will in crea se the poten tia l f o r ICTS, flight tes ting should proceed cautiously as th e flaps are further extended

.

41AC 23.1419-2D 4/19/07
(bb) Critical weight and CG position (n o r m a lly f u ll f o rward at lig ht weight).

(cc) Speeds from 1.2 VS 1 or Reference Landing Approach Airspeed (V REF )-5 knots, as app r o p riate to the wing flap position, up to the m a xi m u m speed to b e encountered operationally in a given flap or gear configuratio n that wi ll n o t resu lt in exceeding Flaps Exten d ed Speed (V FE ) or Landing Gear E x tended Speed (V LE ), as applicable, during the

m a neuver. The speeds V S 1 and V REF m a y have to be redefine d with cr itic a l ic e shapes

.
(dd) Power or thrust: flight idle to m a ximum go-around.

2. Ice Shapes: The applic a n t spec if ies the critic al ic e case (s) f o r investigation in term s of location, shape, thickness, and texture, and obtains FAA concurrence for the ic e shap e(s) to be in vestig ated.

(aa) The critical shape(s ) sho u ld cont ribu te to the la rg est adverse hinge

mom e nt, lowest sta ll an gle, gre a tes t tail lif t loss, and lowest control su rface effectiven ess.

(bb) More than one shape m a y require testing. If a clean wing (no ice accretion) can result in increased negative A ngle-of-Attack (AOA) on th e horizontal tail, ice shapes on the wing should be rem oved. The cri tical ice accretion case( s) should include an allowance f o r the ice sh ape accreted during any ti m e delays in activati on of the ice protection system associated with ice dete ction or observation system s, inte rcycle and residual ice, runback ice, or the accretion that m a y be reasonably expected in service.

(cc) It should b e noted that ice accret ed w ith th e flaps retracted m i ght result in a m o re cr itical c onditi on than ice accreted with the fl aps extend ed. Ice accretion shape and thickness need not be greater than that resulting from exposure to the icing conditions defined in Appendix C to Part 25 or the 45-m i nute hold c ondition of this AC, whichever is m o re critical.

(dd) Ice on th e v e rtical stab ilizer shou ld also be cons idered for the sideslip case.

(ee) ICTS susceptibility should be eval uated with pre-ac tivation ice. In m a ny cases the pre-activation ice m a y be si m u lated by sandpaper ice. A thin ice la yer sim u lated by sandpaper has been found to be criti cal on som e aircraft and should be evaluated along with critical ice accretions on airplanes with a reversible longitudina l control system

.
(ff) Failure conditions of the ice pr otection system should also be addressed. Maxim u m l a nding flap ex tension with a failed ice protec tion system m a y be defined at an interm ediate position. This should beco m e an airplane lim itation for a failure.

3. Z ero-g pushover maneuver. This is a m a neuver to generate a nose down pitch rate so as to increase the angle-of-attack of the air flow over the hor izon tal stabiliz er. Bef o re the m a neuver, the tes t pilo t determ ines in itial en try s p eeds and pitc h attitudes to achieve the target load factor and target airspeed as the airplane pi tches through approxim a tely level flight.

424/19/07 AC 23.1419-2D
(aa) The objective of the pushover m a ne uver is to push the pitch control in the nose-down direction to obtain the te st load f a c t o r (g level) and be at the test airspeed as the nose passes through the horizon. Note any lightening of the pitch control push force during the build-up to the test end. Begi n the m a neuver with the airplane trimm e d or trimm e d as nearly as po ssible at the test power , configuration, and te st (target) speed. The airplane is dived to gain sufficient airspeed above the test airspeed to allow a pull-up (nose above the horizon), followed up by a rapid pitch over as the test airsp eed is app r o ached to ach i eve th e test load factor and airspeed as the nose passes through the horizon.

(bb) The pushover series begins by m oving the control colum n forward while evaluating for any reduction of requi red control force or f o rce reversal. Continue the test poin t s increm entally by increasing th e amp litud e of forward contro l inputs to obtain lower target load f actors until a zero-g flight condition is obtained or, if lim ited by elevator power, to the lowest load factor attain able. The target load factors need to be m a intained long enough to allow an evaluation of the longitudina l force required. During the pitch down maneuver, the test pilot should not change the rate of l ongitudinal control or reverse cont rol m ovem e nt as this m a y alter pitch rate and tail surface geom etry to disqualify that test point.

(cc) For pre-activation ice, when the activation of the ice p r otection system does not require the flight crew to wa it for a specified ice ac cum u l a tion, the pushover

m a neuver can be accom p lished to 0.5 g rather than 0g.

(dd) For f a ilure ice acc retion s, when the f a ilu re is ann unciated to the flight crew and the procedur es are to exit icing conditions , the pushover maneuver can be

accom p lished to 0.5g rather than 0g.

(ee) A push longitudinal control force should be required throughout the test m a neuver. Stop the test if a control fo rc e lightening to less th an zero, or a pull pitch
contro l forc e is requ ired to achieve the test load factor (g level).

(ff) The airplane should demonstrate suitable controllability and

m a neuverability throughout the m a neuver, includ ing recovery, with no tendency to diverge in pitch or other indications of a stalled tailplane.

(gg) During the pitch-down maneuver, any pilot produced change in elevator deflection toward the nose-up di rection disqualifies that test point.

4. Steady state sideslip maneuver. Establish th e airp lane in cr em entally in a straight, steady heading sideslip, up to the sideslip angle appropriate to norm a l operation of the airp lane used to dem onstrate com p liance with § 23.177, Static direction a l and lateral s t ability. The airplane should demonstrate suitable cont rollability and m a neuvera bility throughout the

m a neuver with no tendency to diverge in pitch

.
(c) Other Para meters that May I ndicate a Stalled Tailplane. If the tes t air c raf t is instrum e nted, the following parame ters m a y in dicate a stalled tailplan e:

43AC 23.1419-2D 4/19/07

1. The rela tion s hip of pitch rate ( q ) versus elevator deflection ( δ E ) after the elevator is returned T r ailing Edge-U p (TEU). If stalled, the elevator could deflect substantially bef o re the a i rplane p itch rate s t a r ts to return to zero. This also app ears as reduced elev ator effectivenes s, C m δ E

.

2. If the elev ator stalls, th e aircraft will continue toward zero-g regardless of the f o rce ap plied by the pilot to re tur n to one-g flight. This m a y be determ ined by exam ining the slope of the plot of ve rtical lo ad factor ( N

z ) vs. pitch control f o rce (F ELEVA T OR ) af ter th e eleva t or is
return ed TEU

.

3. Flow visualization m e thods (tufts) w ill usu a lly in dicate the on set of destabilization by flow reversal over a substantial portion of the suction (lower) surface of the horizon tal ta il. This indic a tion of ten a ppears s ligh t ly before pilot tactile force cues. Critical tes t s would have to be repeated without the tufts to de monstrate the tufts have no effect on tail stall.

(4) Compliance by Analysis . For turbo j et powered airp la nes with irreversible, powered pitch control system s, the flight tests described in paragraph 1 3 (e) (2 ) (b ) m a y not be necessary. However, a detailed analysis, as a m i nim u m, should show that:

(a) The airplane has adequate (consult S m all Airplan e Direc t ora t e) m a rgin to tail stall angle o f attack; and

(b) Airplanes of sim ilar size, confi guration and operating envelope have dem onstrated an accep table serv ice h i story with respect to IC TS.

(5) AFM Limitations and Procedures.

(a) Maxim u m l a nding flaps m a y be lim ited to the “takeoff/approach” config uration due to ICTS charac ter i stics, e ithe r with norm a l operation of the ice protection system s or with a f a iled hor izo n tal tail system . This is true r e gard le ss of the cer tif i cation bas i s. Litera l in terpr e ta tion of § 23.1419, am endm ent 23-43 m eans that the aircra ft would have to comply with the 61-knot stall speed in icing at th e takeoff/ap proach flap setting if the f l ap setting was lim ited to prec lude ICTS with norm a l ice protection system operation. The FAA would also consider the exem ption approach described above for the 61- knot rule to address higher stall speeds for those aircraft that lim it f l aps to takeof f / approach se ttin g with ice accretions to p r eclud e ICTS.

(b) If sandpaper ice results in ICTS sus ceptibility and lim ited flap deflection for landing, the AFM procedure for lim iting flap sho u ld be based on visible moisture an d tem p erature rather than airfram e ice accretions if the flight crew cannot see the tail.

f. Pneumatic Deicer Boots. Many AFMs specify a m i nim u m ice accum u lation thickness prior to activation of the deicer boot system . This practice has been in existence due to the belief that a bridge of ice could for m if the boots are operated prem aturely. Flight testing and icing tunnel testing of several “m odern ” boot designs have not shown ev idence of “ice bridging”, and no degradation in ice shedding perform a nce, whe n th e boots were activated at the first sign of ice

444/19/07 AC 23.1419-2D
accretion. Although th e ice m a y not shed com p letely with o n e cycle of the boots, th is residu al ice will be rem o ved during s ubsequent b oot cycles. Tunnel tes t ing is documented in FA A Technical Report DOT/FAA/AR-02/68, "Effect of Residual a nd Intercycle Ice Accretions on Airfoil Perform a nce " (May 2002), and recomm ends th at activating the deicing boots “early and often” are given m o re consideration as a m eans of lim iting the size of in te rcycle and residual ice accretions. “Modern” b oots are d e fined as hi gh operating pressure (nominal g r eater than 15 Pounds Per Square Inch Gauge (PSIG)) and fast inflation and deflation tim es. Both one-inch diam eter tube designs operati ng at a nom i nal 18 PSIG, and 1.75- inch diam eter tube designs operating at a nom inal 15 PSIG, have been eval uated. The tests docum ented in FAA Technical Report DOT/FAA/AR-02/68 were conducted at approxim a tely 175 KCAS. Addition a l tunnel tests at airspeeds typical of m a ny part 23 airplanes are docum ented in AIA A -2007-1090, “Residual and Intercycle Ice for Lo wer Speed Ai rcraft with Pneum a tic Boots.” These tests conducted at 145 KCAS and below, showed that it m a y take m a ny boot c y cles to effectively shed the ice. It m a y appear th at the boo ts are not having any effect at all until shedding occurs. Waiting for a specified amount of ice did not im prove ice shedding. The recomm ended AFM procedure for boot operation should be to operate the boots in an appropria te continuous m ode at the first sign of ice and n o t to wait for a spec ific amount of ice to accum u late. The boots should be operated until icing conditions are exited and ice no long er adheres to the airfram e

.
(1) For applicants that choose to recommend a m easurable ice accum u lation prior to activation of the boots, flight tests in sim u lated or natu ral icing conditions should be

accom p lished to verify that the crew could det ect and recogn ize the sp ecif i ed ice accu mulation thickness. T h e following test criteria have b een accepted for previous flig ht tes t prog ram s :

(a) The pilot or a crewm e mber should be pr ovided a m e ans to detect from his crew position, un der both day and night o p eration, the accum u lation level the a pplicant has specified for activation of the boot syst em for proper ice removal.

(b) The applicant should sh ow that an ice accum u lation m a rgin exists that allows for errors in crew recogn ition of the ice accum u lation level.

(2) In addition, for applicants that choose to recommend a m easurable ice accum u lation prior to boot activation, this pre- activation ice accretion m u st be considered when determ ining critical ice accretions for perform a nc e, stability, control, and stall testing.

NOTE 2: Usually, selection of the deici ng boots to operate causes one cycle of inflation and deflation of all boots, but not necessarily at the sam e ti m e . Som e system s are designed such that all the boots do not com p lete the cycle if the deicing boots are selected off during the m i ddle of one cycle. For these system s, there should be an AFM warning to the flight cr ew to select the ic e protection on for at least one complete cycle of the deicing boots. This note is equally applicable to any deicing system

.
(3) Deicing system s should have a m ode that will autom a tically cycl e the system a f ter activ ation to reduce p ilot workload. For deic ing system s that do not have a tim er to cycle the

45AC 23.1419-2D 4/19/07

system autom a tically on ce activated, the addition a l task of manually cycling deicing system s on pilot work lo ad should be evaluated. A recent part 23 applicant found that definition o f airfram e deicing boot intercycle and resi dual ice steered them toward one-m i nute boot cycles and the workload evaluation dictated an autom a tic tim er for the boots.

g. Emergency and Abnor m al Operating Conditions. Flight investigations should be conducted to verify that, after pilot recogniti on of e m ergency and abnor mal operating conditions, the airplane handling qualities have not deteriorated to the ex tent that the AFM procedures for the condition are ineffective, that AFM procedures a nd recomm e nded airspeeds are safe, and that the airplane can be landed safely. These dem ons trations should be conducted with anticipated residual ice accum u latio n on norm a lly protected s u rfaces. Th e tes t s in Table 5 rep r esent a sam p le

m a trix for a part 23 airplane with failur e ice shap es defined in paragraph 13b(3).

TABLE 5. FAILURE I C E ACCRETION FLIGHT TESTS

Ice Shape Configuration Configuration and Trim Speed Maneuver

One wing zone f a ilure Flaps up and m i nim u m holding • Level, 40-degree banked turns;

• Bank-to-bank rapid rolls, 30 degrees – 30 degrees;

• Determ ine m i ni m u m safe airspeed.

• Approach and landing dem onstration

Em pennage zone f a ilure Full landing flaps and V REF • ICTS evaluation;

• Sideslip s Total wing and

em pennage zone f a ilure • ICTS evaluation

• Level, 40-degree banked turns;

• Bank-to-bank rapid rolls, 30 degrees – 30 degrees;

• Deceleration to stall warning (natural acceptable), recover after one second.

• Approach and go-around dem onstration

Pilot' s windshield ice protection failure Full landing flaps and V REF • Approach and landing dem onstration

464/19/07 AC 23.1419-2D

h. Super Cooled Large Drop (SLD) Conditions . Accidents and incide nts related to loss of airp lane con t rol h a ve raised the con c ern that airplanes operating in certain m e teorological conditions can accrete ice, not only aft of the prot ected areas but also on the wing lower surface. This m a y result in lateral contro l difficulties du e to disturb e d flow over the contro l surfaces, stall at a reduced angle of attack, a nd/or drag penalties. The m e te orological conditions involved are called SLD because they consist of drop sizes larger th an tho s e defined in part 25, Ap pendix C. An inadvertent encounter of such conditions m a y result in an unsafe condition that m u st be addressed. The FAA and EASA are curren tly ha rm onizing rulem a king and guidance for flight in icing conditions that exceed pa rt 25, Appendix C icing conditions. This policy in this paragraph is in th e in te rim and will be replaced when th e ha rm onized regulations an d guidance a r e issu ed for part 23 airplanes.

(1) Roll Control in SLD Co nditions. T h e following guidance, w ith som e modifications, is contained in a July 23, 1997 Policy Mem o randum issued by the Transport Directorate and coordinated with the Standards Office. This policy m e morandum wa s applicable to certain part 25 and part 23 airplanes. In October 1994, a fatal accid ent involving a transport category airplane occurred in which severe ici ng conditions were reporte d in the area. During extensive testing, the accident pr ofile was replicated by ice shapes developed from testing in an icing cloud having drop lets in the size range of freezing d r izzle at a tem p erature near freezing. This condition created a ridge of ice aft of the deicing boots and forward of the ailerons, which resulted in uncommanded m o tion of the ailerons and rapid roll of the aircraft. The NTSB

recomm ended that the F AA develop a tes t proced ure to identify the unsafe aileron hinge m o ment characteristics. The FAA has identified the suscep tibility to loss of contro l following exposure to supercooled large droplets as an unsaf e condition that m a y exist on other aircraft. The FAA is particularly concerned w ith airp lanes that are equipped with n on-powered roll control system s, since non-powered roll flight controls do not have the physi cal advantage of hydraulic or elec trical po wer to ass i st the pilot in overcom i ng the large co ntrol forces that m a y exist from differential pressure res u lting from flow separa tion over the roll con t rol s u rfaces. Th erefore, airplanes certified for flight in icing equipped with non-powered roll control system s should be evaluated for susceptibility to roll upset in the event the airplane is e xposed to certain freezing drizzle conditions.

(2) Stall. In March 2001, a transport category, re gional turboprop airplane reported encounterin g icing cond itions and within s e veral m i nutes exp e rien cing a loss of control in stall, losing approxim ately 8,000 feet before recovering at 10,000 feet. The NTSB determ ined that the lift curv e (s lope and m a xim u m lift coefficient) derived from the flight data recorder w a s signif i can tly lower than the lif t cu rve determ ined by f light te sting sim u late d inte rcycle ice which was develop e d by icing tunnel tests o f part 25, Appendix C co nditions. Th e FAA has identified the redu ctio n in lif t due to supe rcooled large droplets, and subse quently possible stall prior to warning, as an unsafe co ndition th at m a y exist on other aircraft.

(3) Icing Conditions. Ice accretions to be addressed are:

(a) Supercooled droplets having m a xi mu m diam eters of approxim a tely 400 m i crons;

47AC 23.1419-2D 4/19/07
(b) An LWC of approxim a tely 0.33 gram s per cubic m e ter.
NOTE 3: For this condition, the LWC str ongly affects the rate at which the ice feature develops. A higher LWC results in m o re rapid form ation of the ice feature, while a lower LW C results in a slower form ation of the ice feature. The LW C shoul d be adequate to produce an i ce feature during the exposure interval that will s t art to shed on its own acco rd and then refor m

.
(c) A m e dian volum etric diam eter of approxim a tely 170 m i crons.

NOTE 4: The cloud physics instrum e nt ation, calibration, and data processing

m e thodologies should be presented for accep tance by the FAA.

(d) Tem p eratures near freezing such that r unback conditions exist at the stagnation line (as a m i nim u m total air tem p eratures of 24 de grees to 35.5 degrees F s hould be investigated); and

NOTE 5: For this tes t , tem p erature is a critical f actor. Not o n ly is th e tem p erature critical to the developm ent of the ice shape and dim e nsion, static air
tem p erature excursion s above freezin g, a lthough short in du ration, can rev e rse th e ice accretion process.

(e) Operation at holding speeds and holding configurations. L i ght weight and

m a xi m u m possible holding airspeed should be evaluated to obtain lo west possible angle of attack.

(f) An encounter of 20 m i nutes.

(4) Flight Tests

.
(a) Tests. The tests in T a ble 3 should be eval uated at m i ni m u m holding airspeed,

m a xi m u m weight, all possible hold ing configurations and at V REF , m a xi mum weight, all possible approach and landing configuratio ns, except deceleration to stall m a y be stopped at a low speed alarm

, or natural stall warning.

(b) Simulated Ice Shapes. Sim u lated ice shapes rep r esenting th e ice accretions determ ined in paragraph 13.h (3) should be cond ucted. Alternatively, a quarter round, forward facing step shape m a y be flown, with the height calculated analytically based on water catch in the icing conditions in paragra ph 13.h.(3). The shapes should be installed symmetrically along the full span of the wings, behind the prot ected area on the upper and low e r surface.

(c) Pass/Fail C r ite r ia

1. When m a nually flying the airplane :

(aa) There shall be no hazard ous degr adation of the ha ndling qualities of the airplane

.

484/19/07 AC 23.1419-2D
(bb) It should be possible to readily arrest and reverse roll rate using only lateral control input, and the lateral cont rol force should not revers e with increasing control deflection.

2. Any autopilot disconn ec t in a ltitude hold, attitud e hold and h eading hold mode m u st not resu lt in the f o llowin g :

(aa) bank angle of m o re 60 degrees,

(bb) a load on an y part of the struct ure ex ceeding the lesser of eith er the structure’s load lim it or 2g,

(cc) a norm a l acceleration les s than 0 g,

(dd) a roll force greater than 50 lbs. during the recovery action,

(ee) an excess i ve altitude loss

,
(ff) hazardous d e gradation o f the handlin g qualities o f the airp lan e , (gg) engagem e nt or disengagem e nt of a mode leading to hazardous
consequences.

(5) There should be a m eans for the flightcrew to determ ine when the airplane has
enter e d into a supercoo le d large droplet environment, to enable the crew to take appropriate action.

(6) There should be appropriate crew inf o rm a tion provided in the AFM that describes the lim itations and procedures to be observe d while exiting the supe rcooled large droplet environm ent. The FAA has found that the lim itati ons and procedures specified in Appendix 8 of this AC are an accep table m eans of providing this inform ation, unl ess tank er testing h a s shown other cu es o r ice sh ape flight testing has shown other proced ures are m o re appropriate.

14. Ice Shedding. Ice shed from forwar d airp lane s t ru cture could result in dam a ge or erode engine or powerplant components, as well as lifting, stabilizing, a nd flight control surface leading edges. Fan and com p ressor blades, impeller vanes, inlet screens and ducts, as well as propellers,

are exam ples of powerplant com ponents subject to dam a ge fr om shedding ice. For pusher propellers that are very close to the f u selage and well back f r o m the airplane' s nose, ice shed from the forward fuselage and from the wings m a y cause significant propeller dam a ge. Control surfaces such as elev ators, ailerons, flaps, and sp oilers are als o subject to dam a ge, especia lly those that are thin m e tallic, non-m e tallic, or co m posite constructed surf aces. Trajectory and im pinge m e nt analysis m a y not adequately predic t such dam a ge. Unpredicted ice shedding paths from forwar d areas such as radom es and forward wings (canards) have been found to negate the results of this analysis. For th is reason, flight tests should be conducted to supplem ent trajectory and im pingem e nt analysis. If flight tests are not conducted, a dam a ge anal ysis should consider the worst-case ice sh ed event. Video or m o tion pictu r es are excelle nt for docum enting ice

49AC 23.1419-2D 4/19/07
shedding trajectories and im pinge m e nts, while st ill photography m a y be used to docum ent the extent of dam a ge. Any dam a ge should be eval u a ted f o r acc e p tability. In f

light te stin g the airplane should be exposed to an icing condition of m a gnitude and duration sufficient to create the expected wo rst-case ice accretion, in cluding the 45-m i nute hold. Fligh t test evaluation should also account f o r critical , p r edicted trajectorie s in term s of nor mal operational angle of attack and sideslip.

15. Placarding and AFM. This AC provides guidance on airp la nes f o r which the ce rtif ic ation basis requires an AFM. Guidance for AFMs in this AC also applies to A F M supplements.

a. Placarding. Any placarding necess a ry for the safe operation of the airp lane in an icin g environm ent m u st be provided in accordance w ith § 23.1541. Exam ples of such placards are:

(1) Kinds of operation approved (for exam ple, "Flight in Icing C onditions A pproved if Ice Protection Equipm ent is In stalled and Operational”).

(2) Equipm ent lim its (for exam ple, "Ope ration of W i ndshield Anti-Ice May Cause Com p ass De viation in E x cess of 10 degrees)”.

(3) Speed restrictions (for exam ple, "Max im um Speed for Boot Operation—175 Knots Indica ted Airspeed (KIA S))”.

(4) Fluid filler

⎯ inlets for fluid freezin g point de p r essants shou ld bear a pla c ard showing approved fluid type and quantity.

b. AFM. The AFM should provide the pilot with th e inform ation needed to operate the ice protection system and operate in icing conditions. Inform ation should include:

(1) Operating Limita tions Section. S uggested areas to be addressed are as follows:

(a) Lim itations on operating tim e for ice pr otec tion e quipm ent if these lim itations are bas e d on f

l uid anti-ic e /deice sys t e m s capacitie s and f l ow rates.

(b) Minim u m airspeed lim itations for each configuration approved for icing conditions.

(c) Maxim u m airspeed lim itation (if any )

(d) Environm ental lim itatio ns f o r equip m ent ope rations as applicable (for exam ple,

m i ni m u m temperature f o r boot operation, m a xi mum altitud e for boot operation, an d m a xim u m outside air tem p erature for operation of therm a l ice protection system s).

504/19/07 AC 23.1419-2D
(e) A list of all equipm ent required for f light in icing conditions. Section 23.1583(h) (CAR § 3.778) requires that this list be included in the Kind of Equipm e n t List (KOEL).

(f) Minim u m e ngine speed if the airfram e ice protection system does not function properly below this speed.

(g) A list of req u ired p l aca r d s.

(h) Perform a nce lim itations should be presente d for f light in icin g that reflect any effects on lift, drag, thrust, and operating speeds related to operating in icing conditions. These lim itations m a y be presented in the Perform a nce Inform ation section of the AFM and included as lim itations b y specif i c re f e rence in th e Lim itation s section of the AFM

(i) The Lim itations section of the AFM s hould include, as applicable, a statem ent sim ilar to th e f o llowing: “In ic ing co nditions the airplane m u st be operate d, and its ice protection system s used as described in the operating proce dures section of this manual. W h e r e specific operational speeds and perform a nce infor m ation have been established for such conditions, this inform ation must be used.”

(j) The Lim itations section should includ e a statem ent sim ilar to “Takeoff is prohibited w ith any frost, ice, snow or slush a dhering to the wings, horizon tal s t abiliz er , contro l surfaces, pro p eller blad es , or engine inlet.” Modify as applicable or add any other su rface deem ed critica l

.
(k) Visual/Ta c tile Pre-T a ke of f Contam i n ation Check for Turbojet Powered Airplanes

1. Turbojet airplanes without wing leadi ng edge high lift devices. The AFM Lim itations section should also require a visual and tactile insp ection of the wing leading edge and upper su rface in grou nd icing con d itions. Th e Lim itations section shou ld specify a tim e lim it for the tactile check. No m i nally the tactile ch eck must be accom plished within 5 m i nutes of takeoff, except it m a y be accom p lished any tim e between final application of deicin g fluid and takeof f if the airp lane is dei ced in accordance with an approv ed deicing program that com p lies with Section 121.629(c), and takeoff is accom p lis hed within the m a xi m u m holdover tim e in a certificate h o lder' s hold over tim e table. In the cas e of the inab ility to a s cer tain if the f u el
tem p erature is above freezing, the requirem ent to perform a visual/tactile check can be deleted if it can be shown that undetected ice accum u lation does not occur on the w i ng upper surface due to cold soaked fuel. Ground icing cond itions should be defined by the airplane m a nufacturer, bu t

one exam ple is defined as the Outside Air Tem p e r ature (OAT) below 5 degrees C (41 degrees F), or if it cannot be ascertained that the wing fuel temperature is above 32 degrees F (0 degrees C), and one of the following conditions:

(aa) Visible m o isture (rain, drizzle, slee t, snow, fog, etc.) is present; or

51AC 23.1419-2D 4/19/07
(bb) The airplane was exposed to visibl e moisture (rain, drizzle, sleet, snow, fog, e t c.) since th e previous landing; or

(cc) The airp lane experienced in-fligh t ice accretion s i nce the p r ev ious takeoff; or

(dd) The difference between the dew point tem p erature and the O A T is 3°C (5°F) or less; or

(ee) W a ter is p r e s ent on th e wing

2. Turbojet air p lanes witho u t lead ing edge high lift de vices and engines mounted behind wing. The m a nufa cturer should either:

(aa) Show that undetected ice accum u lation does not occur on th e wing upper surface due to cold soaked fuel; or

(bb) Show that undetected ice accum u lation on the wing upper surface caused by cold soaked fuel does no t result in a h azar d to the airp lane due to engine ice inges tion;

or

(cc) Add an AFM Lim itation that requi res a visual/tactile pre-takeoff check if it cannot be ascertai ned that the wing fuel tem p erature is above 32 degrees F (0 degrees C), and the g r ound icing conditions lis t ed above ex ist.

(l) Configuration lim itations, if any (for exam ple, a reduced flap setting for approach and landing, and flaps up for holding or ex tended operations in icing conditions).

(m) Exceedance icing cond itions m a y be prim arily water conten t related for therm a l ice protection system s, prim arily droplet diam eter related for mechanical ic e prote c tion system s or som e com b ination thereof

. For ex ceedance icing conditions that m a y result from environm ental conditions outside the icing envelope established as the basis of the approval defined in part 25, Appendix C, inform ation shoul d be provided as follows (see Appendix 8 of this AC for an exam ple):

1. A m eans to identify an icing condition that exceeds the lim its of the ice protection system for which th e airp lane is certif icated.

2. Recommended procedures and configurations when exiting the exceedance icing cond itions.

3. Procedures to follow during and afte r flight in these conditions in the event of degraded perform a nce or handling ch aracteristics. Info r m ation should include

recomm ended use of flight controls, m i nim u m airs peeds, configuration of high lift devices, drag

524/19/07 AC 23.1419-2D
devices, autom a tic f ligh t guidanc e s y stem , engine power/pro pelle r se ttin gs (as app r o p ria t e), and ice protection system operation.

(n) Autopilot operation should be prohibited if any of the following conditions in icing flight are experienced:

1. Severe icing;

2. Unusual control force or control de flection, or unusua lly large control forces to m o ve flight controls when th e autopilot is disconn ected periodically; or

3. Indications of frequent autopilot retrimming during straight and level flight.

(2) Operating Procedures Section. Section 23.1585(a) requires the pilot be provided with the necessary procedures for safe operati on. The system com ponents should be described with sufficient clarity and depth that the pilot can understand their functio n. Unless flight crew action s are accepted as n o rm al airm anship, the ap propriate p r ocedures sh ould be included in the FAA-approved AFM, AFM revision, or AFM suppl em ent. These procedures should include proper pilot response to cockpit wa rnings, a m eans to diagnose system fa ilures, and the use of the system (s) in a safe m a nner.

(a) Preflight action necess a ry to m i ni m i ze the potential of enroute em ergencies associated w ith the ice protection system should be included when a flight is planned in IMC at
tem p eratures below freezing.

1. Ice protection system s should be checked by operating the system s and verifying proper cockpit annunciations. Mechani cal system s such as pneum atic boots should be visually observed for operation. Fluid system s s hould be visually observed for evidence of fluid along the entire protected span. It m a y take several m i nutes for the entire panels to receive fluid, or the system m a y have air in it, partic ularly after a long pe riod of inactivity.

2. The quantity of fluid in the reservoi r tank, if a fluid ice protection system

, should be checked. The AFM should speci fy the fluid types that are approved.

3. If two sources of electrical power or two pum p s for fluid system s are provided, both should be checked during pre-flight.

(b) Procedures should be provided to op tim i ze operation of the airplane during penetration of icing conditions, in cluding all flight regim e s. Th e AFM should include procedures that adv i se u pon which conditions th e ice p r otection equipm ent should be activ ated.

(c) Em ergency or abnorm a l procedures, incl uding procedures to be followed when ice protection system s fa il and/or warning or m o nitor alerts occur, should be provided.

53AC 23.1419-2D 4/19/07
(d) For fluid anti-ice/deice system s, inform ation and m e thod(s) for determ ining the

rem a ining flight operation tim e should be provided.

(e) For airplanes that cannot supply adequate electrical power for all system s at low engine speeds, load-shedding instructions shoul d be provided to the pilot for approach and landing in icing conditions.

(f) For aircraft equipped with an autopilo t, the autopilot shou ld be disconnected periodically to check for unusual control force or deflection, and to m ove the flight controls to check for ev idence of ice accreting in contro l surface gaps o r frozen actuators. For airplanes no t equipped with an autothrottle, there should be a WARNING that the auto pilot will N O T m a intain airspeed if ice accretes o n the ai rplane. MONITOR airspeed closely.

(3) Performance Informa t ion Section. A brief statem ent that supercooled cloud test environm ent and freezin g rain, freezing drizzle, o r m i xed conditions (as appropriate) have not been tested. These icing environm ental condit ions outside the icing envelope of part 25, Appendix C, m a y exceed the capab ilities of the ice prote c tion system , and it m a y result in a serious degradation of perform a n ce or handling characteristics.

(a) Normal, Utility, and Acrobatic Category Airplanes. For th ese airplan e s, general perf orm a nce inform ation should be provided to give the pilot knowledge of allowances necessary while operating in ice or with resi dual ice on the airfram e. The following item s are only exam ples that provide som e guidelines and are not requirem e nts. These guidelines m a y be revised for specific airplanes as appropriate:

1. An accum u l a tion of inch of ice o n the lead in g edges can cause a loss in rate of climb up to Feet Per Minute (FPM), a cru i se speed reduction of up to KIAS as well as a s i g n ificant buffet and s t all s p eed increas e (up to knots). Even after cycling the deicing boots, the ice accum ulation rem a ining on the boots and unprotected areas of the airplane can cause large perform a nce lo sses. W ith residual ice fr om t h e initial inch accu mulation, losses up to FPM in clim b, KIAS in cruise, and a stall speed increase of knots can result. W ith inch of residual accum u lation, these losses can double.

Exceptions:

● Balked landing clim b data with crit ical ice accretions should be presented in the AFM in the s a m e f o rm at as the basic non-icing data.

● Approach clim b data, if required to be determ ined, should be presented in the AFM in the sam e form at as the basic non-icing data.

● Effects of ice protection system operation and/or ice accretions, if applicable, on takeoff dist ance should be presented.

544/19/07 AC 23.1419-2D

● For airp lane s in which the service c e iling with c r itica l ic e ac cretions is less than 22,000 feet, enr oute clim b perform a nce with critical ice accretions should be presented in the AFM in the s a m e f o rm at as the basic non-icing data.

2. Airspeed—MAINTAIN BETWEEN KIAS AND KIAS with ____ inch or m o re of ice accum u latio n for appropriate configu r ation.

3. Prior to a landing approach cycle th e wing and stabilizer deice boots to shed any accum ulated ice. Main tain extra airspeed on approach to com p ensate f o r th e incre a sed stall speed associated with i ce on unprotected areas. Use cau tion when cycling the boots during an approach, since boot inflation with no ice a ccum u lation may cause m ild pitching and increase stall speeds by knots. It m a y also decrease stall wa rning m a rgin by the sam e a m ount; and it

m a y cause or increase ro lli ng tendency during stall.

4. Holding in icing conditions for longer than 45 m i nutes m a y reduce

m a rgins and could result in inadequate handling and control characteristics.

5. Maintain engine speeds of RPM higher to assure proper operation of the airfram e ice pro t ectio n system

.
(b) Commuter Category Airplanes. D a ta should be provided so that the balked landing clim b lim ited weight and approach clim b lim ited landing weight could be determ ined. These data should include the e ffect of drag due to residual ice on protected and unprotected surfaces, po wer extraction associated with ice p r otection system operation, and any changes in operating speeds due to icing. Also, the effect on landing distance due to revised approach speeds, and/or landing conf igurations, should be shown.

(4) For airp lanes with a cert ification bas i s at am endm en t 23-14 or higher, the AFM should contain a statem ent sim ilar to “This airplane is approv ed fo r flight in icing con d itions as defined in part 25, Appendix C.” For these ai rplanes, there should not be references to operational term s such as “light” or “moderate” ice or “know n icing.”

(5) The AFM should reference the m a intenance m a nual for ice protection surface cleaning procedures if the flight crew can be expe cted to perform this function.

c. Prior to AF M Requirement. If the airp lane wa s certif i ca te d prior to th e ef f ective d a te of the requirem ent for an AFM, then the com b in ation of m a nua ls, m a rkings, and placards should adequately address th e placard and A F M subj ects previous ly discussed in this AC.

16. Instructions for Contin ued Airw orthiness.

a. Requirements. Instructions for Continued Airwor thin ess ( I C A) are req u ired in accordan ce with 14 CFR 21.50(b) and 23.1529. ICA shoul d be prepared in acco rdance with part 23, Appendix G. As a minim u m th e following should be addressed:

55AC 23.1419-2D 4/19/07
(1) Basic description of the ice protectio n system operation, components, and insta lla tion

(2) Servicing infor m ation, such as fluid type and quantities

(3) Location of panels used for inspectio n, and/or ins t ructions to access com p onents

(4) Scheduling infor m ation for each app l i cable com p onent includ ing cleaning

, inspecting, adjusting, testing and lubrication

(5) Overhaul or replacem ent periods for com ponents, if an y

(6) Instru ctions for rem oving and replacing com ponents

(7) Precautions, such as tox i city of freezing point dep r essan t fluid or flamm a bility of

s o me c e me n t s

(8) Cleaning instructions, such as only soap and warm water for pneum atic deicing boots

(9) Lim itations on the m a terials that can be applied, such as ice adhesion inhibitors, rubber preservatives, cosm etic coatings

(10) Recommendations on the fr equency of use of ice adhesion inhibitors

(11) Special equipm ent or m a terials, such solven ts, cem e nts, edge filler, condu ctive edge sealer, rollers for pneum atic boot installation.

b. Fluid Ice Protection Systems. The tailcone, em pennage and other areas aft of the TKS de-icing fluid flow should be insp ected after each use of the ice protection system . This inspection should concentrate on extraneous fluid build-up on electrical contacts, fl ight control surface bearings, b e llcranks, etc. The ice pro t ection syst em fluid evaporates very slowly. Therefore,
contam inates that collect in the fluid in areas of joints, skin laps, etc. m a y cause the acceleration of corrosive action.

c. Repairs for Pneumatic Deicing Boots. Boot manufacturers have developed repair procedures for pinholes, cuts and t ears. The repair process for thes e types of da m a ge is critical because p r o p er operatio n of the boots could be af fect ed. If leaks or pinho les are not p e riod ically repaired, the entire system coul d becom e inoperable if water, dr awn in by the vacuum that holds the boots d e flated, subsequently refreezes and b l ocks a pneu m atic line. The performance of deicing boots is dependent on the height and speed of deicing boot inflation and of the

com position of the surface ply and its ice adh e sio n characteristics. Repairs should not pinch off tubes and thereby reduce inflation height. W ith these concerns in m i nd, the following guidance represents a m i ni m u m that should be addressed for repair procedures:

564/19/07 AC 23.1419-2D
(1) Testing. The following tests shou ld be accom p lished:

(a) Boot Cycle Testing. The integrity of the repair should be evaluated via boot cycling at th e m a xim u m norm a l sy ste m operating pressur e . Cycling shou ld continue u n til the repair or boot fails. The norm a l deflation tim e may be shortened to speed up the test. For

exam ple, a 174-second deflation cycle can be re duced to 18 seconds while m a intaining the six-second inflation time. Any m a terial applied to the whole su rface of th e boot should also be evalua ted in this test.

(b) Cold Temperature Cycling. The testing in (1) (a) should be repeated at a
tem p erature of 0 degrees F or colder.

(c) Hot Tempe r ature. The boots m a y be exposed to hot tem p eratures, especially after on the ground on a hot, sunny day. The combin ation of high tem p e r ature and fluid exposure

m a y cause deterioration and should be evaluated, see paragraph (e).

(d) Proof and Burst Pressure Testing. This testin g should be accom p lished to show com p liance to § 23.1438(b). When conduc ting the proof pressure test at 1.5 tim e s

m a xi m u m operating pressure, the repaired deici ng boot should hold that pressure for 60 seconds and the repair should not fail. After the proof pr essure test, the system should be inflated at

m a xi m u m operating pressure, isolated, and the pre ssure drop verified not to exceed three Pounds Per Square Inch (PSI) in one m i nute.

(e) Fluids Susceptibility. The repair should be exposed to various fluids for at least 24 hours in com b ination with a high tem p er ature (160 degrees F) an d the boots cycled at

nom i nal pressure for at least 24 hours. Fluids to be evaluated include: fuels, oil, hydraulic fluids, glycol/water m i xture, deicing boot ag e reduc tion, surface treatm e nts and ice adhesion p r oducts, and ground deicing flu i d s . One m e thod of accomplishing this test is to so ak a rag with the fluid, place on the deicing boo t over the rep a ir, seal to p r event evap oration, and place in an o v en at 160 degrees F for 24 hours. Following this e xposure the boot is rem oved, and cycled f o r 24 hours. The deicing boot should inflate and hold air, and the repairs should rem a in in place and not leak air.

(f) Sand and Rain Erosion. Sand and rain erosion testing should be

accom p lished to show th at the repair does not ero d e at a g r eater rate th an the boot. A typical sand erosion test is ASTM G-76-95. A typical rain erosion te st is conducted on a whirling arm rig that exposes the boot to a rainfall rate of one in ch per hour at 300 to 500 Miles Per Hour (MPH) (depending on the airpla ne m a xim u m speed); us i ng one to two Millim eter (mm ) diam eter drops.

(g) The inflation height over the repaired area should be m easured and com p ared against other unrepaired portions of the boot at temperatures covering the part 25, Appendix C envelope.

(h) Ice Shedding. Ice shedding performance in the area of the repair, and of the whole boot if any m a terial is applied to the whole boot, should be evaluated throughout the

57AC 23.1419-2D 4/19/07
part 25, App e ndix C continuous m a ximum and inte rm ittent m a xim u m icing conditions. It is particularly im portant to cover the range of tem p eratures and li quid water contents of part 25, Appendix C and the expected operational airspeeds. Sim u lated icing tests, such as an icing tunnel, m a y be used.

(2) Materials P r operties. Any m a terial applied to the boots should be com p atible with the deicing boot m a terial. Use of brittle repair m a terials is not recomm ended. If the boot is

com p letely resurfaced with a m a terial, that m a te rial should b e electri cally conductiv e to allow bleeding of static charge from the deicing boot.

(3) Repair Process Limita tions. The repair process should contain lim itations and quality control procedures such as:

(a) Si z e of repairs. The m a xim u m allowed repair size should be established and tested. Another considerati on is the effect of the repa ir failure on the airplane.

(b) Location and depth of repairs. Can structural elem ents such as tube fabric or stitches be dam a ged or can the wr ong internal layers, such as tube fabric, be bonded together? It is recomm ended that boot m a nufact urers lim its be used.

(c) Density of repairs. The m a xim u m density of repairs (num ber per area) should be tested. It is recomm ended that boot m a nufact urers lim its be used.

(d) Application of solvents and other chemicals. T h e application of solvents and other chem i cals used in the repair process that can disbond the boot should be controlled so that they cannot penetrate inte rnal layers of the boot.

(e) Applicability of the rep air procedu re. Broken stitches re present a structural failure of the boot and should not be repaired. T h ere should also be guidelines as to when severely worn boots should be replaced.

d. Repairs for Electro thermal Propell er and Engine Inlet Deicing Boots. Boot

m a nufacturers historically have not developed repair procedures for electrotherm a l deicing boots because the therm a l m a ss chara c te ris tics of th e re paired loca tion will chan ge and affect ice shedding. T h e following guidance is a m i ni m u m th at should be addressed for electrotherm a l boot repairs:

(1) Testing. The following tests shou ld be accom p lished:

(a) Fluids Susceptibility. The repair should be exposed to various fluids and the boots operated. Fluids to be evalua ted include: fuels, oil, hydrauli c fluids, glycol/water m i xture, deicing boot age, appearance and ice adhe sion products, and ground deicing fluids.

(b) Sand and Rain Erosion. Sand and rain erosion testing should be

accom p lished to show th at the repair does not ero d e at a g r eater rate th an the boot.

584/19/07 AC 23.1419-2D
(c) Thermal Characteristics. The therm a l conductivity of the repair should be evalua ted to insure that it does not provide a “cold spot” on the deic ing boot, resulting from either a higher therm a l m a ss or lower thermal conductivity of the repair m a terial.

(d) Ice Shedding. Ice shedding performance in the area of the repair, and of the whole boot if any m a terial is applied to the whole boot, shoul d be evaluated throughout the part 25, App e ndix C, con tinuous m a xim u m and interm ittent m a xim u m icing conditions

. Sim u lated icing tests, such as an icing tanker, m a y be used.

(e) Vibration. The airplane should be tested in icing conditions to verify the repair on one blade does not directly or indirectly (due to ice shedd i ng) cause un acceptable p r opeller vibration.

(2) Materials P r operties. Any m a terial applied to the boots should be com p atible with the deicing boot m a terial. Use of brittle repair m a terials is not recomm ended. The material should be electrically non-conducti ve and should have sim ilar therm a l conductivity of the deicing boot m a terial. The effect of the chemicals on th e electrical wires or foil should be evaluated.

(3) Repair Process Limita tions. The repair process should contain lim itations and quality control procedures such as:

(a) Si z e of repairs. The m a xim u m allowed repair size should be established and tested. Another considerati on is the effect of the repa ir failure on the airplane.

(b) Location and depth of repairs. Can heating elem ents such as wires o r etched foil be dam a ged or can the resistance of the wi re or foil be altered by the repair procedure?

(c) Density of repairs. The m a xim u m density of repairs (num ber per area) should be tested.

(d) Application of chemicals. Can the application of too m u ch c h em icals penetrate the boot and cause internal debonding of the boot?

(e) Applicability of the rep air procedu re. Can the repair be accom p lished on severely worn boots?

17. Ground Deicing Fluids.
a. Background. Notices (Flight Standards Information Bulletins for Air Transportation, FSAT, prior to 2006) are published yearly by the F AA, containing the latest deicing and anti-icing fluid holdov er tim e guidelines and th e m o st r ecent inform ation available o n operating in ground icing conditions. Airplane opera tors use this inform ation to de velop aircraft ground deicing and anti-icing program s required by 14 C F R §§ 121.629( c) and 135.227(b) (3). Operators who operate under § 135.227(b) (1) or (2 ) m a y still utilize the Notice in form ation as guidance in their ground deicing plan. AC 20-117, AC 135-16, AC 135-17, AC 120-58, and AC 120-60B provide additional infor m ation on deic ing and anti-icing of aircra ft before takeof f.

59AC 23.1419-2D 4/19/07
(1) Why use ground deicing fluids? A i rcraft are deiced be fore takeoff and, as required, anti-iced using thickened pseudo-plasti c fluids. This proce dure provides temporary protection from ice adhering to the ai rcraft’s surf aces before takeoff. The thicker fluid s (Type II, IV) provide considerably higher holdover tim e s than the Type I fluids.

b. Potential Issues. The following have occurred in service resulting in re-designs and modified takeoff procedures and lim itations when certain ground deicing fluids are applied before takeoff.

(1) Performance. The presence of thickened fl uid may affect the airplane’s perform a nce because the fluids m a y not com p lete ly flow off the aircraft wing and lift devices bef o re lif tof f

.
(2) Longitudinal Control. Fluid residue m a y cause increased pilot control f o rces during takeo ff rotation and clim b for airp lanes with reversib le contro l surfaces.

(3) Vibration a nd Controllability. The fluid m a y also collect in the balance bays of aerodynam i cally o r weight balan ced contro l surfaces, due to inadequate d r ainag e . This m a y result in unbalan c ed contro l surfaces, unexp ected ch an g e s in con t rol forces, and contro l surface vibrations. Additionally, there has been one turbojet airp lane in which the el evator tab was found to be ae rody nam i cally se nsitiv e to a c c um ulation of f

o reign mater i als on its surf ace, in this c a se ground anti-icing fluid, caus ing severe vibration a nd lim it cycle oscillations.

(4) Freez ing of Controls. Anti- icing f l u i d m a y collec t and evaporate in quiet cove areas, like those along contro l surface hinge lines. W h en the re sidue of the evaporated anti-icing fluid is re-h ydrated by h u m i dity, rain or during washing of the airp lane, it m a y freeze and lock the
contro l surface when the airp lane climbs to alt itu des with sub f reezing temperatu r es. T h e residu e does not contain a freezing point depressant, us ually a glycol com pound, which evaporates when the anti-icing fluid dries. Rehydrated fl uid has been found in and around gaps between stabilizers, elevators, tabs, a nd hinge areas. This especially can be a problem with non-powered controls. Som e pilots reported that they have had to reduce altitude un til the frozen residue

m e lted, which restored f light control m ove m e nt . This phenom e non has not been experienced when a two-step deicing/anti-icing procedure is used. The first step is generally a hot Type I fluid

m i xture which flushes out residue.

c. When Should These Iss ues Be Addressed? The evaluations of the above issues are not required for showing compliance to 14 CFR § 2 3.1419. Typically the effect of fluids on the airp lane are evaluated by the airf ram e m a nufacturer, after type certi fication

, at the requ est of an operator that is seeking approva l of a ground deicing a nd anti-icing program incorporating Type II or Type IV fluid. However, there are des i gn features, analyses and tests that an airplane

m a nufacturer m a y want to consider during cert if ication to pre v ent re -des igns af ter typ e certification if it is anticipate d operators will u s e ground deici ng/anti-icing fluids. This inform ation is provided in this AC at the request of several airplane m a nufacturers.

604/19/07 AC 23.1419-2D

d. How Should These Issues Be Addressed? Som e issues can be addressed by design. There is currently no req u irem ent to test for ai rplane perform a nce or co n t r o llab ility af ter the application of deice/anti-ice fl uids. The aerodynam ics working group of the SAE G-12 Aircraft Ground Deicing Comm i ttee has been tasked to develop a SAE recomm ended practice for approving the use of fluids on airp lanes. This recommended practice will be considered for part 23 guidance in a subsequent revision to this AC . The following paragraphs summarize m e thods that have been used by m a nufacturers in previous projects to address thes e issues. Th ey are provided to assist airplane m a nufacturers in evalua ting fluids for their specific designs.

(1) Design.

(a) The airplane design should be anal yzed for possible collection sites.

(b) The design should incorporate drain hole s, particularly in control surface balance bays.

(2) Airplane Performance. There have been various m e thods to evaluate perfor m ance. Typically the lowest takeoff gross weight a nd m a xim u m flap position approved for takeoff is considered critical becau se of the lo wer scheduled takeoff rotation speed. Three m e thods that have been used by airplane m a nufacturers:

(a) Takeof f param e ters suc h as tim e to rota te/lif t-of f and rotate /lif t-of f airspe eds have been com p ared during takeoffs with and wi thout fluids. Flow-off of fluids from t h e wing was sim u ltaneously docum ented during takeoff roll and rotation. Stall speed s have been checked at altitude with 1 knot/sec deceleratio ns.

(b) Takeoffs with and without fluids have been perform e d back to back and the lift loss dec r ement at lif tof f determ ined. The f light test m easure d lif t loss w a s then co rre cted by

com putational fluid dynam i cs (CFD) to determ ine the lift loss decrem ent at stall. A 5.24% decrem ent in m a xim u m lift coefficient due to flu i d has been considered acceptab l e for jet powered airplanes, and an 8% decrem ent has b een considered acceptable for propeller powered airplanes.

(c) Takeoffs at fixed pitch angles are perfo r m ed with and without fluid. Several pitch ang l es repres enting the rang e of pitch ang l es at liftoff are tested. A 6% decrem ent in lift coefficient at liftoff has been consid ered sign ificant.

(3) Controllability.

(a) The following has been evaluated at m i ni m u m practical gross weight, with

m i ni m u m approved and m a xi m u m a pproved takeoff flap position, wi th all engines operating:

1. Control power and control force during rotation at the scheduled V R
.

2. Control power and control force during rotation at 10 knots or 7%, whichever is less, be low the scheduled V R
.

61AC 23.1419-2D 4/19/07

3. Controllability tests (± 40o bank an gle changes, ± 0.5g or stall warning) with takeof f f

l aps, as soo n as prac tic a l af ter lif tof f

, eithe r at V 2 +10 or the speed at 50 f e et + 10 KIAS, depending on airplane category.

4. Vibration/buffet at Vne or Vm o.

(b) The f o llowing has been evalua ted f o r m u lti-engine airp lanes at m i nim u m practical gross weight, w ith m a xi m u m approved ta keoff flap position, w i th sim u lated one engine inoperative:

1. Control power and control force during rotation at V R

2. Controllability tests (± 30o bank angle changes, +1.3/-0.8g or stall warning) with takeoff flaps, as soon as practical after liftoff, either at V 2 or the speed at 50 feet, depending on airplane category.

(4) Fluids.

(a) Num b er of Fluids. The airplane m a nufacturer should eval uate the type and brand of fluids to be approved for the airplane . A representative Type II fluid, and a Type IV fluid if approved in the AFM, should be tested. The viscosity of the fluid should be considered when determ ining the brand of fluid to tes t . Typ e III flu i d ne ed not be tes t ed if Type II or IV fluid is tested and showed acceptable lift loss. If the Type II and IV testing showed takeoff procedures needed to be m odified, than Type III fluid m a y not need to be tested if the takeoff procedures for Type III are sim ilarly modified.

(b) Fluid Application.

1. Type II, III, and IV fluids should be applied undiluted.

2

. Procedures f o r de-icing and anti -icing should follow the proposed

recomm ended procedures. All appl icable surfaces (including the horizontal stabilizer) should be treated. Slats/flaps should be in the recomm ende d position for fluid application.

3. Takeoff tests should be conducted as soon as possible following antiicing fluid application.

(c) It is p r eferab le to test at the coldes t o u tside air te mperatur e at which the fluid can be used undiluted.

(5) Airplane Systems. Any adverse effect on aircraft system s should be noted (e.g. ECS, APU inlet, vent blocking)

(6) Post Flight Inspections. Several flights should be conducted after one step applications of the thickened pse udo-plastic fluids to be approved fo r the airplane. Post flight

624/19/07 AC 23.1419-2D
inspections should be conducted to determ ine if flui d residue is present on the airplane in areas that m a y cause one of the problem s discussed in paragraph 17.b.

e. Airplane Flight Manual

(1) Fluids. The type and brands of fluid appr oved, along with any m i nim u m outside air
tem p erature lim itation, should be in the Lim itations section.

(2) Limita tions

. Procedures m odi fied as a result of ground fluids should be in the Lim itations section. Exam ples for part 23 airpla nes are an increase in takeoff speeds and use of fl aps.

(3) Procedures. Pre-flight or post-flight inspecti on and cleaning of areas in which fluid residue is shown to occur.

(4) Performance. Any increases in takeoff distan ce due to takeoff speeds increased above the established threshold should be presen ted in the Perfor m ance section. It should be noted that the takeoff testing is not required to be conducted on contam inated runways. Since
runways m a y be contam inated in co nditions in whic h these fluids will b e used in op eration, there should be a CAUTION that states the takeoff distance data is based on a dry runway, and that takeoff distances will be incr eased on contam inated runways.

f. Instructions for Contin ued Airw orthiness. The following, if app licable, should be addressed in m a intenance m a nual:

(1) Inspection.

(a) Drain holes.

(b) Control balance bays.

(c) Identified aerodynam i cally quiet areas.

(2) Cleaning. High-pressure washing with a hot T ype I fluid/water m i x in areas where fluid could a ccum u late. For those lo cation s equipped with T ype III flu i d s , in lieu of Type I fluid s , it is suggested that a high pressu re washing with a heated Type III/water m i x be e m pl oyed. Such a procedure m a y require subsequent lubrication.

g. Runw ay Deicing Fluids. Airplane m a nufacturers shoul d be aware that since 1997 a problem of c a talytic oxidation has been occurring on aircraft using carbon brakes. In 1997, airports started using m o re environmentally friendly fluids to deice runway s. This resu lted in the use of potassium for m ates and/or acetates. These chem icals (org anic salts) attack the carbon in the brake and create a catalytic oxidation which softens the carbon, causing it to flake and

crum ble undetected and unpredictably over tim e thus reducing the life and long-term efficiency of the brakes them selves. SAE G-12F, am ong other industry working groups, has been working for

63AC 23.1419-2D 4/19/07

som e ti m e to try and red u ce thes e effects from runway de-icers. These runway fluids are now being found to adversely affect anti-icing fluid applie d to aircraft and also to prom ote the for m ation of anti-icing fluid re sidue gel in aerodynam i cally qui et areas o f the aircraft.

644/19/07 AC 23.1419-2D Appendix 1

APPE NDI X 1. DEFI NITIONS

1. DEFINITI ON OF TERMS. For the purposes of this AC, the following definition s should be used.

a. Anti-Ice. T h e preven tio n of ice form ation or accum u lation on a protection surface, either by evaporating the im pinging water o r by allowin g it to run back and off the surface or freeze on non-critical areas.

b. Part 25, Appendix C Icing Conditions. The part 25, Appendix C certification icing condition standard for approving ice protection provisions on aircraft . The conditions are specified in term s of altitude, tem p erature, LW C, repres entative droplet size (MED), and cloud horizontal extent.

NOTE 6: In part 25, Appendix C, the term “ m ean effective diam eter” ref e rs to what is n o w called th e “Median Volu m e Diam eter (MVD),” determ i n ed using
rota ting m u lti- cylind e rs and assum i ng a Langm uir distribu tio n.

c. Artificia l Ice. A structu r e form ed fr om m a terial ot her than frozen water, but intended to
repres ent an ice accretion

. See “sim ulated ice shapes.”

d. Critica l Ice. The aircraft surface ice shape form e d within req u ired icing conditions results in the m o st advers e effects for specific flig ht safety req u irem ents. For an aircraft surface, the critical ice shape m a y differ for different f light safety requirem ents, e.g., stall speed, clim b, aircraft controllability, control surface m ove m e nt , control forces , air data system perform ance, dynam i c pressure probes for control f o rce “feel” adjustm e nt, ingestion an d structural dam a ge from shed ice, engine thrust, engine control, and aeroelastic stability.

e. Deice or Deicing. The periodic shedding or rem oval of ice accum u lations from a surface. This occurs by destroy i ng the bond be tween the ice and the pro t ection surface.

f. Freez ing Drizz l e. Drizzle is precipitation on the gr ound or aloft in the form of liquid water drops that have diam eters less than 0.5 mm and greater than 0.05 mm (100 μm to 500 μm ). Freezing d r izzle ex ists at air tem p eratures less than zero deg r ees C (supercooled), rem a ins in liquid form , and freezes upon contact with objects on the surf ace or airbo r ne.

g. Freez ing Precipitation. Freezing rain or driz zle falli ng th rou gh or outsid e a vis i ble cloud.

h. Freez ing Rain. Rain is precipitation on the ground or aloft in the form of liquid water drops which have diam eters greater than 0.5 mm. Freezing rain is rain that exists at air
tem p eratures less than zero degrees C (superc oo led), rem a ins in liqu i d form , and freezes upon contact with objects on the surface o r airbo r ne.

A1-1AC 23.1419-2D 4/19/07 Appendix 1

i. Ice Crystals

. Any one of a num b er of m acrosc opic, crys tallin e f o rm s in which ice
appears.

j. Icing Conditions. The presence of atmospheric mo isture and tem p erature conducive to airplane icing.

k. Intercycle I ce. Ice that builds up on a deiced surf ace and exists imm e diately before actuation of the deice system

.

l. Liquid Water Content (LWC). The total m a ss of water contained in liquid drops within a unit volum e or m a ss of air, usually gi ven in units of gram s of water pe r cubic m e ter (g/m 3) or kilogram of dry air (g/kg).

m. Mean Effective Diameter (MED). The calculated drop diam et er that divides the total liquid wa ter content p r es ent in the dr op size d i stri bution in h a lf , i.e., half the water vo lum e will be in larger drops and half th e volume in sm aller drops. The value is calculated, based on an

assum e d droplet size distribution, (e.g. Langm uir distribution) which is how it differs from

m e dian volum e dia m eter.

n. Median Volume Diameter (MVD). The drop diam eter that di vides the total liquid w a ter content p r es ent in the dr op distr i bution in half , i. e., half the water volum e will be in larger d r ops and half the volum e in sm aller drops. The value is obtained by actual drop size m easurem ents.

o. Mixed Phase Icing Conditions. Partially glaciated clouds at an am bient tem p erature below 0°C. The clouds contain ice crys tals and supercooled liquid water drops.

p. Monitored Surface. The surface o f concern regardi ng the ice hazard, (e.g., the leading edge of a wing). Ice accretion on the m onitored s u rface m a y be m easured directly o r correlated to ice accretion on a reference surface.

q. Pre-Activation Ice. Pro t ected surface ice accretion prio r to the f u ll ef f ectiveness of th e ice pro t ectio n system

.

r. Protected Surface. A surface containing ice pro t ection, typ i cally located at the surface’s leading edge.

s. Protection Surface. Active surface of an ice protection system , fo r example, the su rface of a deicing boot or ther m a l ice protection system.

t. Reference S u rface. The observed (d irectly o r in direc tly ) surface used as a reference for the pres ence of ice on th e m onitored surface. Th e presen ce o f ice on the reference su rface m u st occur prior to – or coincidentally with – the pr es ence of ice o n the m onitored surface. Exam ples of reference surfaces in clude windshield wiper b l ades or bolts , windshield posts, ice evidence probes, prop eller spinn e r ice, a nd the surface of ice detectors. The reference surface m a y also be the m onitored surface.

A1-24/19/07 AC 23.1419-2D Appendix 1

u. Residual Ice. Ice that rem a ins on a protected su rface imm e diately follow i ng the actuation of a deicing system

.

v. Reversible Flight Cont rols. The flight deck controls th at are connected to the pitch, roll, or yaw control surfaces by direct m echanical linkages, cabl es, or push-pull rods such that pilot effort produces m o tion or force about the co ntrol surface hinge line . Conversely, force or motion orig inating at the contro l surface (through aerodynam i c loads, static im balance, or trim tab inpu ts, f o r exam ple) is tr ansm itte d back to f l ight deck con t rols.

(1) Aerodynamically Boosted Flight Controls: Reversible flight control sy stem s that

em ploy a movable tab o n the trailing edge of th e m a in control surface link ed to the p i lot' s contro ls or to the structu r e in such a way as to produce aerodynam i c forc es that m ove , or help to move, the su rface. Am ong the vario u s for m s are flying tabs, geared o r servo tabs, an d spring tabs.

(2) Pow er-Assisted Flight Controls: Reversible flight cont ro l system s in which som e

m eans is provided, usually a hydraulic actuator, to apply force to a control surface in addition to that supp lie d by the pilo t to enab le large surf ace deflections to be obtained at high speeds.

w . Runback Ice. Ice form ed from the freezing o r ref r eez ing of water leav ing an area on a n aircraft surf ace that is above freezin g and flowing downwind to an area that is sufficiently coo l ed for freezing to take p l ace. This ice ty pe is frequently a byp ro duct of partially ev aporative (running wet) ice protection system s, therm a l deic ing systems, and can occur on airfoils near freezing temperatu r e.

x. Simulated I ce. Ice shapes that are fabricated from wood, epoxy, or other m a terials by any construction technique.

y. Supercooled Large Drops (SLD). Supercooled liquid water that includes freezing rain or freezing d r izzle.

z. Supercooled Drops. Water drops that rem a in unfro zen at temperatures below 0°C. Supercooled drops exist in clouds, freezing d r izzle, and freezing rain in the atm o sphere. These drops m a y impinge and freeze after contact on aircraft su rfac es

2. DEFINITI ON OF ACRONYMS.

AC Advisory Circular ACO Aircraf t Cer tif ica tion Of f i ce AFM Airplane F l ight Manual AIR Aerospace Infor m ation Report AOA Angle of Attack APU Auxilia ry Power Unit ARP Aerospace Recommended Practice AS Aerospace S t andard

A1-3AC 23.1419-2D 4/19/07 Appendix 1

ATC Air Traffic Control C Centigrade CAR Civil Air Regulations CFR Code of Federal Regulations CG Center of Gravity CS Certif ica tion Specif i catio n (EASA) ELOS Equivalent Level of Safety F Fahrenheit FAA Federal Aviation Adm i nistration FPM Feet Per Minute FSAT Flight Stand a rds Information Bulletins for Air Transporta tion EASA European Aviation Safety Agency EFIS Electronic F light Information System s FIDS Flight Ice D e tection System s ICA Instru ctions for C ontinued Airworthiness ICTS Ice Contam inated Tailplane Stall IMC Instrum e nt Meteorological Conditions IPS Ice Protectio n System KCAS Knots Calibrated Airspeed KIAS Knots Indicated Airspeed KOEL Kind of Equipm ent List LOUT Lowest Operational Use Tem p erature LW C Liquid W a ter Content MDI Magnetic Direction Ind i c a tor MED Mean Effective Diam eter M FC Maxim u m Mach num ber for stab ility characteristics MMEL Master Min imum Equipm ent List MOC Means Of Com p liance MSL Mean Sea L e vel MVD Median Volum e Diam eter NASA National Aeronautics an d Space Adm i nistration NTSB National T r ansportation Safety Board OAT Outside Air Tem p erature PFIDS Prim ary Flight Ice Detection System s PMA Parts Manuf acturing Approval POH Pilot' s Operating Handbook PSI Pounds Per Square Inch PSIG Pounds Per Square Inch Gauge RGL Regulatory and Guidance Library RPM Revolutions Per Minute SAE Society of Autom o tive Engineers SLD Supercooled Large Drops STC Supplem ental Type Certificate TC Type Certificate TCDS Type Certificate Data Sheet

A1-44/19/07 AC 23.1419-2D Appendix 1

TEU Trailing Edge Up TSO Technical Standard Order V FE Flaps Exten d ed Speed VIT Variable Incidence Tailplane V LE Landing Gear Extended Speed V MC Minim u m Control Airspeed V MO Maxim u m Operating A i rspeed M MO Maxim u m Operating Mach Num b er V NE Never Exceed Airspeed V R Takeoff rotation speed V REF Reference Landing Approach Airspeed V 2 Takeoff safe t y speed

A1-5 (and A1-6)4/19/07 AC 23.1419-2D Appendix 2

APPE NDI X 2. GUIDELINE S F O R DET E R MI NING CERTIFICATION BASIS ON FLIGHT IN ICING APPROVAL STCS AND AMENDE D TCS

1. My CAR 3 (or earlier certific ation basis) aircraft has ice protection systems installed and is not placarded against flight into know n icing. Am I approved for flight in icing conditions?

These CAR 3 airp lanes are perm itted to fly in icin g conditions if:

• the ic e prote c tion sys t em s are in sta lle d per t ype design data of the sam e model in the Type Certificate Data Sheet (TCDS);

• the Pilot’s O p erating Handbook (POH), AFM, or AFM supplem ent associated with the ice protection system s do not prohibit it;

• the equipm ent lis ted in the KOEL is insta lled and f

unctioning ; and

• the airplane com p lies with the equipm ent requirem e nts of § 91.527 or § 135.227, if applic able.

2. What if I h ave a CAR 3 (or earlier certification basis) airplane that is permitted to fly in icing conditions but I replace the ice pr otection system w i th another system?

It depends on what is m eant by another system . I f it is replacem ent parts, such as replacing
pneum atic deicing boots with thos e from another m a nufacturer, the c e rtif ication b a sis can rem a in unchanged; see Appendix 5 of this AC for m o re info r m ation. If it is another type of system , for

exam ple replacing a pneum atic deicing system w ith a freezing point depressant system or electrothermal system , c o m p liance to § 23.1419, am endm ent 23-14 m u st be shown. Section 23.1419, amendm ent 23-43 would not be required si nce a m odification to an ice protection system is considered “not signifi cant” under the Changed Product Rule.

3. As a follow

- up to the last question, suppose I change my mind and want to re-install my ice protection systems. Will my aircra ft be approved for flight in icin g?

Yes, as long as the sys t em s are installed pe r type design data and the POH, AFM, or AFM supplem ent associated w ith th e ice p r otection sy s t em s do not prohibit flig ht in icing conditions (or “flight into known icing”). Retroactive rem oval of flight into known ici ng approval can only be accom p lished by the airworth ines s directiv e p r ocess.

4. I have a CAR 3 (or earlier certifica t ion basis ) airplane that has no ice protection system installed and the type design data does not co ntain fligh t in icing approval. What is the certificatio n basis if I add ice protection sys t ems?

Under the Changed Product Rule, adding approval fo r flight in icing cond itions is con s idered a significant change (AC 21.101-1) and com p liance should be shown to the latest am endm ent. In

A2-1AC 23.1419-2C 4/19/07 Appendix 2

addition, § 91.527 or § 135.227, if applicable, has a m i ni m u m requirem e nt of equipm ent. The applicable regulations for an icing certification are:

23.603 23.1093 23.1301 23.1327 23.1501 23.1581 23.773 23.1095 23.1309 23.1351 23.1525 23.1583 23.775 23.1097 23.1323 23.1357 23.1529 23.905 23.1099 23.1325 23.1416 23.1547 23.929 23.1101 23.1326 23.1419 23.1559

It is recognized that complianc e to § 23.1419(a), which requires that the airplane m eet Subpart B perform a nce in icing conditions, m a y be im practi cal for som e CAR 3 airplanes. The Changed Product Rule allows the applicant to elect com p liance to am endm ent 23-14 for that particular paragraph of § 23.1419. In this case the perform a nce regulations are used as guidelines as discussed in paragraph 13a (2) of this AC.

5. My airplan e has some ice protection systems installed but is not cer tif i ed for f ligh t in icing. A lat er model o f my airplan e , w h ich is on the same TCDS, is c ertified for flight in icing in accordance w i th § 23.1419. The later mo del does have a different engine installed

w i th higher horsepow er and a different ice prot ection sys t em. Can I install the exact same ice protection systems as the la t er model, ins t all a new engi ne w i th at least the sa me horsepow er, and be certified for flight in icing ?

Yes, and sim ilarity m a y be used to show com p liance to the applicable regulations. However, there m a y be som e testing required. The cu rrent m e thod of com p liance to § 23.1419 includes tests (susc e p tibility to ice contam inated tailplan e stall, for example) that may not have been

accom p lished during certificat ion of the later m o del.

A2- 24/19/07 AC 23.1419-2D Appendix 3

APPE NDI X 3. GUIDELINE S F O R SUPPL EMENT A L TYPE CE RTIFICAT ES (STC) AND AME NDE D TYP E CE RTIFI CAT ES ON AIRPL A NES

1. APPLICAT ION.

a. As stated in the “APPLICABILITY” section, the guidance in this AC applies to any STC or a m ended TC on an airplane f o r wh ich the applicant w a nts approval under the provisions of § 23.1419. Increase in gross wei ght, changes in engine power, and propeller changes could affect approval in icing and thes e areas would have to be evaluated using AC 23.1419-2D as the m e thod of com p liance. An app licant wishing to use an alternate Means of Com p liance (MOC) needs to consul t the Standard s Office. Whethe r the ce rtif ic ation b a sis f o r the STC or am ended TC includes 14 CFR, § 23.1419 at am endm ent 23-14 or 23-43 is irrelevan t as far as the tests that shou ld be accom p lished. Th e difference in the c e rtification basis does n o t change th e tests that must be accom plished, only their pass/fail criteria

.

b. Com p liance to icing regulations has been either an aftert hought or totally disregarded

on m a ny m o dification program s on a i rcraft cert i f ied for fl i ght i n icing conditions. In som e cases, th e rationale used was that s i n ce the i ce protection system s were not m odified, icing regulations do not need to be addressed. Th is may be an incorrect assum p tion. Icing regulations m a y need to be addressed for any modification that could affect th e follo wing in icing conditions:

(1) Aircraft pe rform a nce

(2) Flying qualities,

(3) Engine operation

(4) Essential system operation.

c. If it is d e sire d to re tain f l ight in icing approval of the m odified airplane, the following

exam ples are m odifications in which com p liance to icing regulations need to be revisited:

(1) Engine changes

(2) APU
(3) Propeller changes

(4) Engine inlet or acce ssory inlet changes

(5) Antennae installations or ot her external m odifications

(6) Gross weight increases

(7) CG envelope increase

A3-1AC 23.1419-2D 4/19/07 Appendix 3

(8) Flight envelope increase

(9) Turboprop conversion

(10) Modificatio ns to lifting surfaces

(11) Installation of vor tex generators

(12) Modifications to ice protection system s

(13) Addition of/or re-location of fuel vents

(14) Addition of /or autop ilot repla cem ent.

d. The icing regulations that are addressed in this appendix are:

(1) § 23.929

(2) § 23.1093

(3) § 23.1301

(4) § 23.1309

(5) § 23.1416

(6) § 23.1419

e. The following guidance address som e specific, comm on modifications:

(1) Engine Changes.

(a) Effects o f in creased eng i ne pow er or thrust:

1

. On airplan e s with a ce rtif ication basis at am endm e n t 23-14 or higher, any degrada tion in s t a ll charac ter i stics, stab ility or control, or m a rginal characteristics, due to increased en gine power or thrus t , will require re -evaluation with ice accretions. Since the pass/f a il cr iteria are qua lita tive, testing (orig i nal airplane and m odified airplane) should be

accom p lished back to back by the sam e test pilo t. Stall warning should also be evalu a ted. Although the m a rgins are not a concern at high powe r, they need to eval uate if higher power

m a sks any stall warn ing cues. The following tests should be accom p lished:

(aa) Stall characteris tics and st ability of m i ni m u m weight and

m a xim u m weight, af t C G lim it

A3-24/19/07 AC 23.1419-2D Appendix 3

(bb) Controllability at forward CG li m it and critical weight.

2

. Susceptib ility to ice contam inated tailplane st all should be addressed for airp lanes in which the en gine th rust increas e is g r eater than 1 0 percen t or the airplan e has a service history of ICTS susceptibility. Maxim u m pow er is us ually m o re critica l than idle. This cannot be done with analysis on a propeller airpla ne with reversible controls due to second order effects. Flig ht testing sh ould be acco mplished with 40-grit sandpaper and intercycle/residual ice on horizon ta l ta ilplane, intercy c le /res idual ice on ve rtical stab ilizer, and 4 5 -m inute ice accretions on unprotected lead ing edge tail surf aces.

• Engine Induction Icing . Refer to AC 23-16A for guidance.

(c) Ice Shedding. Engine com p liance data to § 33.77 should be com p ared between the currently installed engine and the pr oposed engine. If the ice slab used to show

com p liance is sm aller for the proposed engine, ice shedding from the airfram e should be readdressed. Data on ice shedding m a y be available from the airplane TC holder. Engine inlet lip ice shedding should be addressed. The am oun t of ice m a ss that could be shed should be

com p ared to a sim ilar, approved engine instal lation or to part 33 engine com p liance data.

(d) Effects o f Decreased E n gine Pow e r, Thrust or Bleed Air

.

1

. Ice Protection System Operation. Bleed air mass flows, pressures and tem p eratures of the proposed engine and of the existing, certified engine should be

com p ared. If there is a reduc tion, the effectiveness of the ice protection system s m u s t be substantiated.

2 . Airplane Performance. Airplane perform a nce in icing conditions should be re-evaluated.

(2) Essential A P U. W h en an essentia l APU is m o dif i ed or added, operation in icing conditions should be addressed sim ilarly to engines since essential APUs are covered by § 23.1093.

(3) Propeller C h anges.

(a) Section 23.929 states that propellers (e xcept wooden propellers) and other engine in stallations m u st be protected agains t the accum u latio n of ice as n ecessary to enable satisfactory functioning without appr eciable loss of thrust when operated in the icing conditions f o r which ce rtif ic ation is requested.

(b) If the deicing system is listed on the propeller T C DS, it does not indicate that

com p liance to § 23.929 was shown. It m eans that the deicing system wa s shown to function properly, the deicing system comp lies with prope ller structu r al and vibration regulations, and deicing system failure modes, as discusse d in § 23.929 of AC 23-16, cannot cause an unairworthy condition.

A3-3AC 23.1419-2D 4/19/07 Appendix 3

(c) The typical analysis report from the deicing boot m a nufacturer is not sufficient by itself to show com p liance to § 23.929. The typical report calc ulates intercycle ice thickness for various flight and icing conditions, but doe s not calculate the effect on propeller efficiency, which m u st be done to show no appreci able loss of thrust. F o r STCs, it would be acceptable to show that intercycle ice is equal to or less than th e accretion s obtain e d o n the sam e propeller on an airplane that was flight tested in icing c onditions and shown to have no
apprec iable loss in thrus t

.
(d) The typical deicing boot m a nufacturer repo rt als o contain s a caveat that it does not address propeller runback ic e. Sim ilarity to another propell er tha t was f light tested in icing conditions is usually done to address r unback. Sim ilarity would include propeller and deicing boot aerodynam i c and thermal sim ilarity, de icing cycle tim e, prope ller RPM, and flight conditions. Note that m e tal and composite propellers have different therm a l m a sses.

(e) As a final qualitative check for bot h intercycle and runback ice on new airplane program s , airplane perfor mance is checked during flight test s in icing conditions. A test point as close to m i nus 22 degrees F as possi ble should be included in the flight tests.

(f) The propeller installation, including spinner and cowl geom etry, m u st be

com p ared to previously tested installations in icing condition s. Changes that could allow moisture to reach the b r u s h blocks must be avo i d e d.

(g) If the proposed propeller is calculated to have higher efficiency than the existing, approved propeller, the guidance in paragr aph 1e (1) (a) of this appendix should be f o llowed.

(h) If the proposed propeller(s) and/or deici ng system are predicted to increase the size of intercycle ice, the effect s of propeller ice shed onto other parts of the airplane should be addressed.

(i) For New Propeller Deice Electrical Pow er Systems:

1

. The surface tem p erature characteristic s of the pro p eller boots should be shown to be the sam e as origin al ce rtif ied system

.
(aa) If the tem p erature characteristic s an d deice tim ing cycle are shown to be changed, flight testing in m easured natu ral icing conditions are required to evaluate propeller deicing and airplane perform a nce

(bb) If the tem p erature characteristic s an d deice tim ing cycle are shown to be unchanged, a dem o nstration of propeller deicing and airplane perform a nce in natural icing conditions should be perfor m ed.

(cc) Flight testin g should be accom p lis hed as close to –22 degrees F as possible.

A3-44/19/07 AC 23.1419-2D Appendix 3

2

. A rational analysis of the heat generated by the system should be m a de and com p ared to the existing sys t em if the syst em is located in area s where ice accretion and runback could be affected, such as the spinner.

(4) Engine Inlet or Accessory Inlet Ch anges. Guidance is p r o v ided in the “engine changes” section above. It should be noted that § 23.1093 applies to eng i ne oil and accessory cooling inlets as well as induction inlets.

(5) Antennas, Installations or Other E x ternal Mo difica tions.

(a) When antennas, cam eras, fairings for su ch installations, or other external installations such as drain m a sts are installed on aircraft, the inst aller should show the following:

1

. The predicted ice accretion does not contribute significantly to drag;

2

. There is no ice-shedd i ng hazard due to im pact or ingestion on downstream structure, engines or propellers. See paragraph 14 of the AC for guidance on ice shedding.

3

. There is no ice related perform a n ce reduction of lifting surfaces;

4

. There is no ice related effect on dow nstream air data sensors or ice detectors.

(b) A very cons ervative, s imple analys is m a y be accom p lished first to show the objectives (a) 1 and (a) 2. If th e conservative analysis fails, the analysis can be refined to determ ine if the in itial an alysis was o v erly cons ervative. The conservative analys is can assum e the f o llowin g :

1

. The water catch area is the full frontal area of th e installatio n;

2

. Collection efficiency is one.

3

. No runback or evaporation of i m pinging water.

4

. Assum e the shape on bla d e antenna will be s i m ilar to a i rf oils and the shape on low profile antennae will be single horn shapes.

(c) The installer should determ ine the cri tical icing condition, an d the 45-m i nute hold in con t inuous m a xi mum conditions needs to be includ ed . If the analysis shows a problem

, then one or more of the following can be accom p lished :

1

. Determ ine realistic collection efficiency eith er w ith an ice accretion code or with the “FAA Icing Handbook”;

A3-5AC 23.1419-2D 4/19/07 Appendix 3

2

. Determ ine the rea l im pingem e nt limits by using an icing code, which m a y reduce the c o llec tion a r e a ;

3

. Run the f u ll conf iguratio n in an ic ing code to de te rm ine if the insta lla tion is in a shadow zone.

4

. If drag is a problem , run an ice a ccretion code to determ ine a more realistic ice shape.

(d) Flight tests in m easured natural icing or with sim u lated ice shapes should be

accom p lished to determ ine if there are any detrim ental effects due to th e ice accretion s if:

1

. The installation is upstream of air da ta sensors or an ice detector; or

2

. The insta lla tion is on a lifting surface or

3

. The installation could create a wake on a lifting s u rface. As an exam ple, if an external m odification is large enough (e.g. dish antenna), it m a y interfere with the flow field around the tail and the susceptibility to ICTS m a y need to be addressed.

(e) The one exception to (d) 2 is fairings. An analysis to show the im pact on

m a xim u m lif t coef f i cient, in com b ination with flight tests with no ice accretions, m a y be acceptable.

(6) Gross Weig ht Increases.

(a) At the increased angle of attack for a given airspeed, the im pingem e nt limits will chang e

. An i m pingem e nt analysis needs to be accom p lished to sho w the ice p r otection
coverage rem a ins adequate.

(b) The im pingem e nt analysis should also eval uate unprotected areas such as fuel
vents.

(c) If the f o llowing f light tes ting with no ice show no degradation from the

unm odified aircraft, and no m a rgin al charac ter i stics, f light tes ting with ice (or sim u late d ice accretions ) are not required:

1

. Stall wa rnin g, stall cha r a c ter i stics, and stability at m a xim u m weight, aft CG li m i t

2

. Stall sp eeds and contro llability a t m a xim u m weight, forward CG li m it.

(d) Operational speeds and AFM/POH perform a nce data in icing conditions need to reflect higher stall speeds.

A3-64/19/07 AC 23.1419-2D Appendix 3

(e) C lim b perform a nce in icing conditions shoul d be evaluated to determ ine if the airplane is capable of operating safely.

(f) An analysis should show increased w e i ght m a kes the airplane equal or less susceptible to tailplane stall. The an alysis s hou ld evalua te ta il trim require m e nts and tail ice accretion at the higher airp lane angle of attack.

(7) CG Envelope Increase. Generally, the sam e guidance used f o r gross weight increases can be used for CG envelope increases . The one exception is w h en an increase of forward center of gravity lim it on airplanes m a kes an airplane m o re susceptible to ice
contam inated tailplane stall. This should be addressed by flight tes ting f o r

airp lanes with unpowered, reversible elevators o r with prop ellers. An analy s is m a y be acceptab l e for other configurations.

(8) Flight Envelope or Operating Procedure Changes.

(a) If an increase in m a xi m u m operating al titude is ap plied for, th e applicant should demonstrate:

1

. The ice protection system opera ting pressures (f or pneum atic system s) or tem p eratures (for hot air system s) by dry air testing; and

2

. The stall speeds and stall characterist ics asso ciated with ice accretions if these are shown to be influenced by Mach number.

(b) The effect of increased cruise airsp e eds and increased altitudes that could affect windshield ice accretion, and adequacy of the windshield heat, should be addressed.

(c) The ef f ect of dif f e rent operating airs peeds and a l titud e s tha t c ould af f e ct critical ice accretions.

(9) Turboprop Conversion.

(a) If the ice p r otection sys t em s utilize engine bleed air for operation, th e pneum atic lines m a y accum u late m o re water than the current unm odified type design. This
water can su bsequently refreeze and block the pn eum a tic lines, resulting in failure of s o m e or all zones of the pneum atic system . The applicant ne eds to show that the pneum atic deicing system will con tinu e to f unction in ic ing con d itions.

(b) The pneum a tic deicer operating pressure m a y also decrease at lower engin e RPMs. A minim u m engi ne RPM for acceptable p n eum a tic operating pressure, which should allow for descent, should be estab lished and published in the AFM/POH.

A3-7AC 23.1419-2D 4/19/07 Appendix 3

(10) Modificatio n s to Lifting Surfaces.

(a) Critical ice accretions (i ncluding pre-activation, in tercycle, residual, and runback) m a y have to be re-defined, especially if the changes affect wing angle of attack. Stall strips are good collectors of ice and are an example where leading edge ice accretions should be re-defined. If ice accretions ar e changed or the m odifications could affect control power or
contro l surface hinge m o m e nts, flight test ing with sim u lated ice accretion s should be

accom p lished to evalu a te one or m o re of the following:

1

. Stall wa rnin g, stall cha r a c ter i stics, and stability at m a xim u m weight, aft CG lim it;

2

. Stall sp eeds, stall warnin g, contro llab ility and pe r f o rm ance at m a xim u m weight, f o rward CG lim it;

3

. ICTS susceptibility at light weight, fo rward CG lim it if the air c raf t has unpowered, reversible elevators or propellers.

4

. For unprotected winglets, flutter m a rgins needs to be addressed.

(b) Susceptibility to ICTS should be addressed for either horizontal or vertical tail modifications or wing modifications that a r e pr ed icted to inc r ease ICTS susceptibility. ICTS susceptibility m a y be addressed by analysis on jet- powered aircraft with irreversible elevator controls.

(11) Installation of Vortex Generators.

For vortex generators that are installed n ear the leading edge, the applicant should provide data on expected ice ac cretions. Flight conditions to consider are the 45-m i nute hold, descent, and approach. Substant iation of the effects on s t all speed s, stall characteristics, and stability and control should be provided.

(12) Modificatio n s to Ice Protection Systems.

(a) Critical ice accretions m a y have to be re-defined. If ice acc retions are changed or the m odifications coul d affect control power or contro l surface hinge m o ments, flight testing with sim u lated ice accre tion s should be accom p lished to evalu a te o n e or m o re of the following:

1

. Stall wa rnin g, stall cha r a c ter i stics, and stability at m a xim u m weight, aft CG lim it;

2

. Stall speeds; stall warning and contro llability at maxim u m weight, forward CG lim it;

A3-84/19/07 AC 23 1419-2D Appendix 3

3

. ICTS susceptibility at light weight, fo rward CG lim it if the air c raf t has unpowered, reversible elevators or propellers.

(13) Addition of or Re location of Fuel Vent.

As a m i nimum an im pingem ent analysis and/o r sim ilarity should be used to show that ice does not obstruct the fuel vents.

(14) Addition or Replacement of Autopilot

Guidance in this AC, paragraphs 12 and 13 for autopilots should be consulted. There are specific scenarios in which autop ilots can get the pilot into troubl e in an airplane approved for flight into known icing. Those scenarios resulted in acciden ts and are factual. Based on our service experience, even though there are no regul atory requirem e nts addressing autopilots in airplanes approved for known icing, a pplicants are strongly encourag ed to include features that

m itigate these autop ilot induced accident scen arios. W h ere it would be impractical to add such a feature, th e design should include ad equate trim in m o tion cu es. For rep l acem ent autopilots, the design of the original and replacem e n t autopilo ts should be com p ared.

A3-9 (and A3-10)4/19/07 AC 23 1419-2D Appendix 4

APPE NDI X 4. GUIDELINE S F O R CERTIFYING ICE PROTE C TION SYS TEMS ON AIRPL ANES NOT CERTIFICAT ED F O R FLIGHT IN ICING

1. APPLICABILITY. There m a y be tim es when applican ts m a y want to certificate an ice protection system installation on an airplane that is to rem a in not certificated for flight in icing. This used to be called a “non-hazard ” basis. This m eans that the ai rcraft is prohibited from flight in ic ing con d itions bu t there is som e ice pro t ec tion to f acilita te an ex it f r o m an inadve rten t ic ing encounter. The following guidan ce provides a reference; novel system s m a y require additional considerations.

2. SUBPART B – FLIGHT.

a. The applicant m u st show that installation of the system (not operating) does not affect perform a nce, stalls, controllability, maneuve rability, stability, trim , ground/water handling, vibration and buffet, and, if appli cable, high speed characteristics. If any of these are affected, it should be sh own that ap plicab le reg u lations ar e still com p lied with a nd p l ace the appropriate inform ation in the AFM. Com p liance should be acco m p lished with dry air f light tests. If the system is being evalu a ted as an am ended TC or ST C, it is no t necess a ry to investigate all weigh t and CG combinations and flight conditions when results from the airplan e certif ication testing clea rly ind i c a te th e m o st critica l com b ination to b e tes t ed.

b. In som e cases the effect of system operati on m a y need to be evaluated. For pneum atic deicing boo ts, the operation of the bo ots (inflatio n) should have no hazard ous affect on airp lane perform a nce and handling qualities. The effect of pneum atic boot operation on stall speed and stall warnin g should be evaluated an d appropria te inform ation placed in the AFM. Freezing point depressant system s when operating have been shown to increase drag.

3. SUBP ART D – DESIG N AND CO NSTRUCT I ON.

a. The ice protection system s should be evaluated to determ ine the im pact to the airfram e structure per the applicable regulations in subpa rt D. The load conditions determ ined from Subpart C should be used in this evaluation. The individual ice prot ection system components should also be evaluated to determ ine that th ey would withstand the load conditions from Subpart C if their failure can cause a hazard. Therm a l effect s on structure of therm a l ice protection system s and fluid/stru cture com p atibil ity of freezing point dep r essan t system s should be evaluated.

b. An evaluation of flutter characteristics to ac count for the added m a ss of t h e ice protection system s should be m a de per § 23.629.

c. If a therm a l windshield ice prot ectio n system is installed, an evaluation of the visibility due to distortion effects through the p r otecte d area should be m a de. In accordance with § 23.775(g), a probable single failur e of a transparency heating system should not adversely affect the integrity of the airplane cab in or create a potential danger of fire.

A4- 1AC 23.1419-2D 4/19/07 Appendix 4

d. For wing and em pennage electrical deicing sy stem s, the indirect effects of lightning

m a ybe an issue. The airplane m u st be shown to be protected against catastrophic effects from lightn i ng in accordan ce with § 23.867. As a m i nim u m the effect of the ice protection system installation should be addre ssed by analysis and design.

4. SUBPART E – POWERPLANT. For an airplane not certif icated for flight in icing,

com p liance to § 23.929 is not required but com p liance to § 23.1093 is required.

5. SUBP ART F – EQUIP M ENT.

a. On airplan e s with a ce rtif ication bas i s of a m endments 23-20 and higher, com p liance to § 23.1301 must be show n. Com p liance to § 23.1301 would entail showing the airplane can safely exit inadvertent icing encounters by provi ding the data in paragraphs (1) through (5). Subsequent installations on other aircraft m odels can be based upon sim ilarity to the natural icing tests that were conducted provided that the installations can be shown to be sufficiently sim ilar (ref. paragraph 10.f.). Airfoil size, shape, opera ting envelope, and airplane ice accretion sites should be included in th e sim ilarity analysis:

(1) A functional flight test in dry air

(2) Icing tunnel tests in part 25, Appendix C icing co nditions

(a) Evaluate the ice pro t ection system operation

(b) Determ ine protected area ice accreti on such as runback, intercycle ice

(3) Em pirical flight test data (natural icing or tanker)

(a) Validate ice accretions f o r ice sh ape flight testing

(b) Evaluate and docum ent susceptibility of m ovable control surfaces to fixed surface brid ging/freezin g and subs equent locku p of controls

(c) Evaluation of autopilot operation and recomm ended operation in icing

(d) Qualita tive l y evalua te clim b perf ormance

(e) Evaluate degradation in windshield visibility

(4) Dry air ice s h ape flight tests

(a) Ice shap es

1. Five m i nute accretions o n unprotected areas

A4-24/19/07 AC 23.1419-2D Appendix 4

2. Protected area ice accretions

(b) Objectiv es

1. Evaluate sta b ility and controllability

2. Evaluate increase in stall speed.

b. Com p liance to the latest applicable am endment of § 23.1309 should be shown. See AC 23.1309-1C for additional guidance. To show com p liance to § 23.1 309 the follo wing would apply:

(1) Show that installation of the system , and norm a l operation of the system , does not affect operation of essential equipm e n t. Exam ples are:

(a) Electrom a gnetic inte rf ere n ce tes ting

(b) Operation of the stall warning system.

(2) Show that hazards are m i nim i zed on singl e engin e airp lanes and prevented for multi-eng i ne airp lanes in the even t of a probable f a ilu re. Exa m ples of f

a ilures tha t sho u ld be addressed:

(a) Auto inflation of deicing boots

(b) Failures that could cause an asymm e t r ic wing condition

(c) Bleed air leaks of therm a l system s
(d) Electrical sh orts in electrotherm al sys t em s.

(3) Com p liance can be by analysis or test or a com b ination. The loss of the ice protection system woul d not have to be considered since the airplane is not approved for flight in icing. For the purposes of the current regulati on, the system would not be an essential load.

(4) Show that the system when operating norm a lly does not create a greater hazard than operating with no ice protection system. For ex ample, on system s where there is runb ack the applicant should show that the r unb ack ice do es not cause a great er hazard than the ice accretion with no ice protection. Hazards to address would be st alls, tailp lane stalls, and engin e operation if

applicab le

.

c. To show compliance to § 23.1351 an electrical load analysis should be done if the ice protec tion s y stem utiliz es the a i rp la ne’s pr im ary elec trical p o wer system . If the ice p r otec tion system utilizes its own alternator/gen erato r , other regulations in § 23.1351 m a y be applicab le.

d. Com p liance to § 23.1416 and § 23.1419 are not required.

A4-3AC 23 1419-2D 4/19/07 Appendix 4

6. SUBP ART G – OPERATING LI MITATIONS AND INFORMATI O N.

a. A cockpit placard in view of the pilo t and the AF M should state th at th e airplane is prohibited from flight in icing conditions.

b. A description of all ice prot ection system controls and annunciations should be in the AFM.

c. The AFM should caution that stall warning in icing conditions m i ght not be reliable and must not be relied upon in icing cond itions, even with a heated stall warning sensor.

d. Stall speeds with the system in stalled or system operating, if increased from the baseline airplane, should be published in the AFM. An increm ental delta increas e m a y be used for all configurations, if appropriate.

e. Procedures to m itigate lo cked controls due to ice accreti on, if applicable.

f. Autopilot operation procedures.

(1) For aircraft equipped with an autopilot, the autopilot shou ld be disconnected periodically to check for unusual control force or deflection, and to m ove the flight controls to check for ev idence of ice accreting in cont ro l surface gaps o r frozen actuators.

(2) There should be a WARNING that the autopi lot will NOT maintain airsp eed if ice accretes on the airp lane. MONITOR airspeed clo s ely.

g. Instructions for continue d airworthiness in accordance with § 23.1529 should be provided.

A4-44/19/07 AC 23 1419-2D Appendix 5

APPE NDI X 5. GUIDELINE S F O R A PPROVAL OF REPL ACE M ENT PART S FOR AIRF RAME DEICI N G SYST E M S

1. The requirem e nts leading to a pproval of replacem ent airfram e deicing system s (propellerdeicing system s will be addressed in a revis i on) or airf r a m e therm a l deicing or anti-ic i ng system s are functions of the project cert if ication basis an d sim ilarity w ith the o r ig inal pa rt(s), as summarized in Table 5-1 and discus sed in the following paragraphs:

TABLE 5-1. SUMMARY OF TEST REQUI RE MENTS FOR REPL ACEMENT AI RFRAME DEICING C O MPONE NTS

Aircraft Approved for Flight in Icing

Conditions? Certif ica tion Basis Approval Process Required Tests to Sho w Safe Operation throughout Part 25, Appendix C Icing Conditions Natural Icin g Flight Tests

No PMA Not required Not required

Yes CAR § 3.712 STC See paragraph b. See paragraph b.

Yes 23-0 to 23-13 STC See paragraph b. See paragraph b.

Yes 23-14 to 23-42 STC Required See paragraph c.

Yes 23-43 or higher STC Required Required

a. For aircraft whose certifi cation basis does not include CAR § 3.712 or § 23.1419, the deicing system is optional equipm ent and not req u ir ed. In this case, th e replacem ent parts can be approved via the Parts Manufacturer Approval (PMA ) process in 14 CFR, part 21, subpart K. The replacem ent parts must be shown to functi on properly, rem ove ice or preven t ice accretion as well as th e previous ly insta lled eq uipm ent, not introdu ce a ddition a l f a ilure m odes that could prevent continued safe flight and landing, and not affect stall charac teristics, stability or control of the airp lane in dry air. Com p arative tes t s of th e orig inal versus the replacem ent parts are acceptable to show how the part rem oves or prev ents ice accretion.

b. For aircraft whose certificat ion basis is CAR § 3.712 or an original issue under § 23.1419, an STC is required. Original certific ation of these aircra ft only required that
pneum atic deice r s be in s t alled per ap proved data and that the y have a pos itiv e m eans of deflation. N o icing flight test s were required, and airplanes w e re considered “approved for flight into known icing” when the airplane was equipped with a complem e nt of certificated deicing or anti-icing equipm ent spelled out in operational requirem e nts. For replacem ent parts in these airc raft it is advisab l e for the Aircraf t Certificatio n Office (ACO ) to contact th e ACO

m a intaining the or igina l type design d a ta to d e te rm ine factors such as variance with th e orig inal design, the original certif ication requirem ents, and the service history of the original product.

A5-1AC 23 1419-2D 4/19/07 Appendix 5

The replacem ent parts must be shown to f unction properly, rem ove ice or prevent ice accretion as well as the p r evious ly in stalled equ i p m ent, and not introduce additional failure modes that could prevent continue d safe flight and la nding. Com p arative test s of the original versus th e replacem ent parts m a y be acceptable. If the orig in al certification basis is to be utilized, it is highly r ecommended that an entry in the AFM supplem ent lim itations section, or a placard, with the following wording be require d: “This airplane has not dem onstrated

com p liance with the icing environm ent requ irem ents of 14 CFR, part 25, Appendix C.

c. For replacem ent parts on an aircraft whose certification basis is § 23.1419,

am endm ents 23-14 through 23-42, an STC is required. Flight testing in m easured, natural icing conditions should be accom plished if the replacem e nt parts are of differe nt m a terials or have different design characteristics. Supplem e ntal te sting in artificial icing conditions (icing tunnel, tanker) should also be accom p lished to cover th e com p lete part 25, Appendix C envelope. The replacem ent parts m u st be shown to function pr o p erly, rem o ve ice o r prev ent ice acc retion as well as the p r evious ly in stalled equ i p m ent, and not introduce additional failure m odes that could prevent continued safe flight and landing. A m a trix of perf orm a nce and flying qualities as discussed in paragraph 1 3 a (2) of this AC s hould be accom p lished. The Standards Office shou ld be contacted since the requirem e nt to flight test in m easured, natural icing conditions is dependent on a num ber factors such as whether AFM perform a nce in icing conditions is based on protected surface ice accr etions, the service history of th e airp lane, an d flight te sting

accom p lished during th e origin al certification wi th protected s u rface ice accretions. Fo llow-on applic ation s of the new parts in aircr a f t other th an the in itial c e rtification m a y then be approved through sim ilarity provided the conditions in § 23.1419(c) are m e t. There m a y be cases where

m i nor m odifications would not require additional m easured, na tura l f light tests.

d. For replacem ent parts on an aircraft whose certification basis is § 23.1419,

am endm ent 23-43 or higher or those aircraft wher e the applicant wants to add “flight in icing conditions” operational approval, an STC is required. Flight test ing in m easured, natural icing conditions is required if the replacement parts are of different m a terials or have different design characteristics. Supplem ental testing in sim u lated icing co nditions (i cing tunnel, tanker) m a y also be required to cov e r the com p lete part 25, A ppendix C envelope. Th e replacem ent parts must be shown to function properly, rem ove ice or preven t ice accretion as well as the previous ly installed equipm ent, and not introduce failure m ode s that could prevent continued safe flight and landing. A m a trix of perform a nce and flying qualitie s as discussed in para graph 13a (1) of this AC should be accom p lished. Follow-on applications of the new parts in aircraft other than the initial certification m a y then be approved through sim ilarity provided the conditions in § 23.1419(c) are m e t. There m a y be cases wh ere m i nor m odifications would not require additional m easured, natural flight tests.

2. Engineering judgm ent must be used to determ in e that the m o difications would not affect the effectiveness of the ice protection in natural icing conditions. If there is any question as to the need for a particular design to be subject to natural icing tests, the ACO should contact the Standards O ffice as well as the ACO that perfor m e d the original c e rtif ica tion and the nationa l resource specialist for aircraft icing. Again, seemingly benign differences can have significant negativ e effects on an aircraft ' s ice protection capability.

A5-24/19/07 AC 23.1419-2D Appendix 6

APPENDI X 6. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDM ENT 23-43

1. In acco rdan ce with § 23 .1419(a), A m endment 23-43, "capab le of operating safely" means that airplane perform a nc e, cont rollability, m a neuverabi lity, and stability m a y be degraded from the non-iced airplane but m u st not be less than the requi rem e nts in part 23, subpart B. Guidance for each sub p art B regu lation, as related to icing, is in th e following Table 6-1.

2. The definition of “capable of operating safely” is not defined in the regulation at Am endm ent 23-14. For airplanes with a certif ication basis before 23-43, the test s and pass/fail criteria in the Table 6-1 should be used as a guide to develop a test program . Th e regula tions ita lic iz ed in the table are not typically addr essed in showing compliance to § 23.1419 at am endment 23-14.

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43

Regulation 14 CFR Section Guidance

Proof of

com p liance 23.21 Only critical weight and CG lo adings, as determ ined during the noncontam inated airp lane tests, are re qu ired. Natur a l icing f ligh t tests

m a y be accomplished at a nom inal CG.

Load distribution lim its 23.23 Only critical weight and CG lo adings, as determ ined during the noncontam inated airp lane tests, are requ ir ed. Tests in which late ral load is critical, such as stall character istics, should include tests with

m a xi m u m allowable fuel asymm e try.

There should not be different load, weight, and CG li m its for flight in icing. Operation in icing conditions should be essentially transparent to the flightcrew in that no icing-specific m e thods of operation (other than activating ice protection syst em s) should be required. T h is philosophy is also based on hum a n fa ctors issues to reduce operational

com p lexity and flightcrew workload.

General (Perform ance) 23.45 Must com p ly, except perform a nce should be determ ined up to a
tem p erature of standard plus fi ve degrees C instead of plus 30 degrees C. It can be assum e d th at ice accretio n will not b e present on the airfram e at te m p eratures warm er than plus five degrees C. For deicing system s, the average drag in crem ent and propeller ef ficiency determ ined over the deicing cycle may be used for perform a nce calculations. Propeller deicing c odes do not address propeller runback icing. Sim i larity to previously flight-tested configurations or qualitative perform a nce evaluati ons in natural icing should be

accom p lished.

A6-1AC 23.1419-2D 4/19/07 Appendix 6

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 (Continued)

Regulation 14 CFR Section Guidance

Stall speed 23.49 Must com p ly with critical ic e accretions. See paragraph 13a (1) (c) for

exem ption considera tion s to the 61 -k not stall speed requirement. Stall speeds with critica l i ce accretions should be determ ined and published in the AFM.

Takeoff speeds 23.51 When determ ining the takeoff speeds V 1 , V R , and V 2 for flight in icing conditions, the values of V MCG and V MC determ ined for non-icing conditions m a y be used. If the st all speed with “takeoff” ice at

m a xi m u m takeoff weight with takeoff flaps, gear retracted ex ceeds that in non-icing conditions by m o re than the greater of three KCAS or three p e rcen t V S1 , the speed at 50 f eet or V 2 m u st be increased to

rem a in complian t

.

Takeoff perform a nce 23.53 The effect of operating ice prot ection system s on engine perfor m ance should be accounted for.

Takeoff perform ance in icing conditions m u st be calculated w ith “takeoff” ice if:

a. The stall speed with “takeoff” i ce at m a xi m u m takeoff weight with takeoff flaps, gear retracted exceeds that in non -icing conditio ns by more than the greater of th ree KCAS or three perc ent V S1 ; an d

b. If commuter category, the degrad ation of the gradient of clim b determ ined in accordan ce with § 23.67(c)(2) is greater than onehalf of the applicab le actual-to-net takeoff path gradient reduction defined in § 25.61(b); and

c. If m u lti- engine norm a l, utility or acroba tic c a tegory, the degradation of the gradient of c lim b determ ined in accordan ce with § 23.67(a) or (b) is greater than one-half of the applicab le actual-tonet takeoff path gradient re duction defined in § 25.61(b).

Acceleratestop distance 23.55 Applicable for comm ute r category only. The effect of any increase due to takeoff in icing conditions m a y be determ ined by analysis.

A6-24/19/07 AC 23.1419-2D Appendix 6

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 (Continued)

Regulation 14 CFR Section Guidance

Takeoff path 23.57

Takeoff distan ce and takeoff run 23.59 Applicable for icing for commute r category only if the conditions described above in 23.53 are m e t. May be calculated by a suitable analys is.

Takeoff flight path 2 3

. 6 1

Clim b: general 23.63 Must be compliant with critic al ice accretions, except am bient
tem p eratures above 41-degrees F do not need to be addressed.

Clim b: all engine operating 23.65 Must be shown to be compliant w ith engine power losses associated with operating ice protection equipm ent that are not prohibited for takeoff. Climb perfor mance losses due to ice accretion are n o rm ally not appropriate below 400 feet sinc e the airplane should not depart with ice on the airplane. However, if ice pro t ection system operation is prohibited for takeoff or the AFM does not specifically prohibit takeoff with frost on the wing and control su rfaces, effect of ice accretions m u st be cons idered if:

a. the stall speed with “takeoff” ice at m a xi m u m takeoff weight with takeoff flaps, gear retracted exceeds that in non -icing conditio ns by more than the greater of th ree KCAS or three perc ent V S1 , and

b. for airplanes in which 23.65(a) is applicable, the degradation of the gradien t of clim b determined in acco rdance with § 23.65(a)) with “takeoff” ice is greater than 1.6 percent, and

c. for airplanes in which 23.65(b) is applicable, the degradation of the gradien t of clim b determined in acco rdance with § 23.65(b) with “takeoff” ice is greater than 0.8 percent.
*Takeoff climb: one engine inoperative 2 3

. 6 6 I f applicable m u st be compliant.

* Italicized regulations indicate tests not typically accom p lished for 23.1419 at

am endm ent 23-14.

A6-3AC 23.1419-2D 4/19/07 Appendix 6

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 (Continued)

Regulation 14 CFR Section Guidance

Clim b: one engine inoperative 23.67 The effect of operating ice prot ection system s on engine perfor m ance must be accounted for. The effect of ice accretion on clim b perform a nce (lift, drag and clim b speed) m u st be accounted f o r if:

a. The stall speed with “takeoff” ice at m a xi m u m takeoff weight with takeoff flaps, gear retracted exceeds that in non -icing conditio ns by m o re than the greater of th ree KCAS or three percen t V S1 ; and

b. If commuter category, the degr adation of the gradient of clim b determ ined in accordan ce with § 23.67(c)(2) is greater than onehalf of the applicab le actual-to-net takeoff path gradient reduction defined in § 25.61(b), and

c. If m u lti- engine norm a l, utility or acroba tic c a tegory, the degradation of the gradient of clim b determ ined in accordan ce with § 23.67(a) or (b) is greater than 0.3 percent.
For paragra phs (b) (1 ), (c) (1), a nd (c) (2), “takeoff” ice applies, and for paragrap h (c) (3 ) “Final Takeoff” i ce app lies, rathe r than c r itica l ic e accretions.

Enroute clim b/desce n t 23.69 Must be determ ined with “Enrout e” ice if the enroute clim b s p eed selec t ed in icing is m o re than th e non-icing speed by the greatest of three KCAS or three percent V S1 , or if the service ceiling with “Enroute” ice is less than 22,000 ft. MSL. The enroute clim b speed must be at least th e m i nimum airspeed specified in the AFM lim itations section.
Glide: single engines airp lanes 23.71 If applicable and if ice protect ion system s becom e inoperative with engine out, the best glide speed in ic ing m u st be determ ined if different from the non-icing speed by m o re than three KCAS. May be determ ined analytica lly.

Reference landing approach speed 23.73 Must be based on stall speed w ith c r itical ice a c c r etion if V REF in icing exceeds V REF in non-icing conditions by m o re than 4 knots at

m a xi m u m landing weight. The V MC determ ined for non-icing conditions m a y be used if the vertic al tail does not have ice accretion in norm a l system operation. If based on the non-ice V REF , the airplane with critical ice ac cretions should still com p ly with the stall w a rning and m a neuver m a rgin requirem e nts of § 23.207.

A6-44/19/07 AC 23.1419-2D Appendix 6

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 (Continued)

Regulation 14 CFR Section Guidance

Landing distan ce 23.75 Must be determ ined with critical ice accretion if V REF in icin g conditions is greater than V REF in non-icing conditions by m o r e than four knots. The effect of la nding speed increase on the landing distance m a y be determ i n ed by analysis.

Balked landing 23.77 Must be compliant with critical ice accretions, all ice protection system s operational, all landing fl ap settings, at an am bient
tem p erature of 41 degrees F.

2 3

. 1 4 3 If the non-icing V MC is used for takeoff speeds, it m u st be shown that the airplane is saf e ly cont rollable and m a neuv erable at the mi n i mu m V 2 for takeoff with the critical engine inoperative and with “takeoff” ice accretion.

If the non-icing V MC is used for V REF , it m u st be shown that the airplane is safely controllable and m a neuverable during a go-around starting at the m i ni m u m V REF with the critical engine inoperative and with cr itical i ce accretion

. Susceptibility to ICTS should be ev aluated with critic al ice accretions, sandpaper ice and pre-activ ation ice as discussed in paragraph 13.e. of this AC. Susceptib ility to control anom alie s in SLD conditions as discussed in paragraph 13.h. of this AC should be addressed.

Longitudinal control 23.145 The tests in paragraphs (a) a nd (b) (1) and (b ) (2) must be

accom p lished. For the o t her tests, th e results fro m the noncontam inated airplane tests should be reviewed to determ ine whether there are an y cases where there was m a rginal compliance. If so, or if qualitative evaluations w ith ice ac cretions show control anomalies, these cases should be repeated with ice. Controllability m a y be degraded from the non-iced airplane but m u st still be com p liant. Analysis, the results of the non-ic ing tests to show com p liance to § 23.145(e), and the results of controll ability tests with ice accretions

m a y be used to show compliance to § 23.145(e).

A6-5AC 23.1419-2D 4/19/07 Appendix 6

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 (Continued)

Regulation 14 CFR Section Guidance

General (contro l) 23.141 Must be sho w n to be compliant with critical ice accretions.

Directional and latera l control 2 3

. 1 4 7 C r i t i c a l conf iguration(s) determ ined from the non-contam inated airplane tests m u st be evaluated. Analysis, the results of the non-icing tests to show com p liance to § 23.147(c), and the results of
contro llab ility tes t s with ice ac cre tion s m a y be used to show

com p liance to § 23.147(c).

M i n i mu m control speed 23.149 If the vertical tail is unprotected or has intercycle/residual/runback ice during ice protection system nor m a l operation, V MC speeds with critical ice must be evaluated to determ ine if the proposed V REF speed in icing complies with § 23.73. Static V MC tests m a y be used.

Acrobatic

m a neuvers 23.151 Not applicable for icing certification.

Control during landings 23.153 Must be sho w n to be compliant with critical ice accretions.

Elevato r contro l forc e in m a neuvers 2 3

. 1 5 5 C r i t i c a l conf iguration(s) determ ined from the non-contam inated airplane tests m u st be evaluated.

Rate of roll 23.157 Airplane m u st com p ly with “takeoff” ice accretions for paragraph (a) and critical ice accretion s for paragr aph (b). Controllability m a y be degraded from the non-iced airplane but m u st still be com p liant. Tests should be conducted with 1/3, 2/3, and full roll control authority. In addition, to check fo r hinge m o m e nt reversals other roll
contro l ano m alies, perf orm this te st with holding ice accretions,

m i ni m u m holding speed, at m a xi m u m weight, at all approved holding configuratio ns. Recovery roll cont ro l should no t be initiated until the airplane has rolled through 50 degree bank.

Trim 23.161 The results from the non-contam inated airplane tests should be reviewed to determ ine whether th ere are any cases where there was

m a rginal compliance. If so, or if qua litativ e eva l uations with ice accretions h o w any control anom alies, these cases should be repeated

A6-64/19/07 AC 23.1419-2D Appendix 6

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 (Continued)

Regulation 14 CFR Section Guidance

Trim (Cont.) 23.161 (Cont) with ice. Otherwise, no dedicate d te sts with ice accretions re quired, qualitative evaluations can be acco m p lished concurrently with other
tests.

General (stab i lity) 23.171 Must be sho w n to be compliant with critical ice accretions.

Static longitud i nal stability 23.173 Stability m a y be degraded from the non-iced airplane but m u st still be

com p liant.

De m onstration of static longitud i nal stability 2 3

. 1 7 5 C r i t i c a l conf iguration(s) determ ined from the non-contam inated airplane tests m u st be evaluated.

Static directional and latera l stability 23.177 Must evaluate steady heading sid e slips in acco rd ance with paragraph (d). These tests should check for hinge m o ment reversals about the lateral and directional axis up to full rudder deflection. The results from the non-contam inated airplane tests to show com p liance with paragraphs (a) and (b) should be re v i ewed to determ ine whether there are any cases where there was m a rginal com p liance. If so, these cas es should be repeated with ice. Stab ility m a y be degraded from the noniced a i rplan e but m u st still b e com p liant.

Dyna m i c stability 2 3

. 1 8 1 C r i t i c a l conf iguration(s) determ ined from the non-contam inated airp lane tests m u st be evaluate d with critical ice accretions.

W i ngs level stall 23.201 As a m i nimum wings level stalls with cruise, approach and landing flaps, power off and on, should be evaluated with critical ice accretions. Roll m a y slightly exc eed 15 degrees if characteris tics qualitatively determ ined to be safe. Stall chara c teris tic s shou ld also b e evalua ted when the a i rplane is s t alle d with the a u topilo t eng a ged, unless the design of the autopilot pr e c ludes its ab ility to ope ra te beyond stall warning. For these desi gns the controllability at stall warning should be evaluated. Recovery at stall warning should also be

A6-7AC 23.1419-2D 4/19/07 Appendix 6

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 (Continued)

Regulation 14 CFR Section Guidance

W i ngs level stall (Cont.) 23.201 (Cont.) evaluated by only applying engine power or thrust. Evaluations should be accom p lished by trimm i ng at m i ni m u m AFM icing airspe ed, se tting th e auto pilot in altitude hold (for turns comm anding a heading change), reducing power/t hrust to establish a 1 kt/sec deceleration rate, and at stall warn in g apply power/thrus t. Evaluate the aircraft response, need for dire ctional/lateral c ontrol, airspeed incre a se, an d altitude lo ss (assu m i ng autopilot will dis c onn ect as designed at stall warning).

Turning flight and accelerated turning stalls 23.203 Turning stalls should be evalua ted with critical ice accretions sim ilarly to wings leve l stalls. Ac ce lera ted tu rning st alls not required unless tests with no ice show m a rginal com p liance. Stall characteristics should also be evalua ted when the airplane is stalled with the autopilot engaged, unle ss the design of the autopilot precludes its ability to operate beyond stall warning. For these designs the autopilot op eration up to stall warn in g and contro llab ility at stall warning s hould be evaluated.

Stall warning 23.207 (a)-(c) Should be evaluated concurrently with stall speed and stall characteristics tests. The type of sta ll warn ing with c r itica l a nd preactiv ation ice accretion s should be th e sam e as with the non

contam inated airp lane. The stall wa rning m a rgin with cr itic a l ic e accretions should be co mpliant. Fo r pre-activation ice, the m a rgin can be less than the Sub p art B requ irem ent but it should be po sitiv e and shown to be adequate. Biasing of the stall warning (resetting trigger points to lower angles of attack when ice protection is initiated) m a y be required to achieve acceptable m a rgins to stall. The

m e thod of bi asing should be evaluated. Adequacy of stall warning when airplane is decelerated with autopilot engaged, and recovery at stall warning with power only, should be evaluated.

Maneuver

ma r g i n 23.207 (d) 40-degree bank level altitude tu rns and 30 degree/30 degrees bank-tobank rolls at the flight conditions specified in the regulation should be accom p lished to dem onstrate th e airp lane is free of buffet and stall warning with critical ice accretions . All takeoff and approach flap settings should be evaluated. For one-engine inoperative evaluations, only a 30-degree turn is necessary, a nd the appropriate thrust m a y be sim u lated with a ll eng i n e s opera ting at a reduced power/thrust.

A6-84/19/07 AC 23.1419-2D Appendix 6

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 (Continued)

Regulation 14 CFR Section Guidance

Accelerated stall warning

ma r g i n 23.207 (e) Not required unless tests with no ice show m a rginal com p liance.

S p i n n i n g 2 3

. 2 2 1 Not r e q u i r e d

. Longitudinal stability and control 23.231 Must be shown to be compliant.

Directional stability and control 23.233 Must be sho w n to be compliant with critical i ce accretions. The results of the steady heading sides lip tests with c r itical ice m a y be used to establish the saf e cross wind com ponent. If the flight test data show that the m a xi m u m sideslip angl e dem onstrated is s i m ilar to th at dem onstrated with the non-contam inated airplane, and the flight characteristics (e.g., control forces and deflections, bank angle) are sim ilar, then the non-contam inated airplane crosswind com p onent is considered valid.

If the results of the com p aris on discussed above are not clearly sim ilar, and in the ab sen ce of a m o re rational analysis, a conservative analysis based on the results of th e steady heading sideslip tests m a y be used to establish the safe cr osswind com pone nt. The crosswind value m a y be estim a ted from :

V CW = V REF * sin (sideslip angle) /1.5 where:

V CW is the crosswind component,

V REF is the landing reference speed a ppropriate to a m i ni m u m landing weight, and sideslip angle is that d e monstrated at V REF
Operation on unpaved surfaces 23.235 Not applicable for icing certification.

A6-9AC 23.1419-2D 4/19/07 Appendix 6

TABLE 6-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43 (Continued)

Regulation 14 CFR Section Guidance

Operation
on water 23.237 Not applicable for icing certification.

Spray characteristi

cs 23.239 Not applicable for icing certification.

Vibration and buffet 23.251 The non-icing tests sho u ld be acco mplished with the ice protection system s installed.

Should be qualitatively evaluated in conjunction with other dry air ice shape f light tests up to th e lower of :

2 5 0 K C A S V MO /M MO /V NE A speed at which it is d e m onstrated that the airf ram e will be f r ee of ice accretion.

Vibration due to pr opeller icing/de-icing shoul d be evaluated during the natu ral icing te sting.

High speedcharacteristics 23.253 If applicable, com p liance should be shown with airfram e ice protection system s installed. Not requi red with ice accretio ns.

A6-104/19/07 AC 23.1419-2D Appendix 7

APPE NDI X 7. ICE CONTAMINATE D TAI L PLANE S T AL L (ICT S) BACKGROUND

1. BACKGROUND. When the leading edge of a horizon tal tailp lane bec o m e s conta m inated with ice accretions, control of th e aircraft m a y be severely a ffected. The ICTS phenom e non in its ex trem e form m a y result in an unc ontrollable nose-down pitching event.

a. What is IC TS? ICTS occurs due to airflow separation on the lower surface of the tailplane that is caused by the angle-of-attack of the horizontal tailplane being increased above the redu ced stall angle-o f -attack that can resu lt w h en even small quantities of ice have for m ed on the ta ilp lane leading edg e . The incr e a se in tailpla n e angle

- of -atta ck can r e sult f r om airplane configuration (for example, in creas ed flap extens ion inc r eas i ng the downwash angle or trim required for the CG position) an d/or flight conditions (for example, high approach speed resulting in reduced tail angle-of -attack, gusts, m a neuvering or engi ne power changes). ICTS is characterized by a reduction or loss, som e ti m e s sudden, of pitch control or stability while operating in, or recently departi ng from

, icing conditions. For airp lanes with longi tudinal control system s that are not pow ered (reversible control system s), the pressure differential between the upper and lo wer surfaces of the st alled tailplane m a y result in a high elevator h i nge mom e nt, forcing the elevator trailing edge down. This elev ator hinge mom e nt revers al can b e of sufficient

m a gnitude to draw the control co lumn forward with a level of fo rce that is beyond the com b ined efforts of the flightcrew to overcom e. ICTS re duces ta il lif t o r dim i nishes the ef f ectiv eness of the prim ary and secondary contro l su rfaces. Di minished control effectiveness ranges from reduced elevator authority to s udden, large and unexpected changes in required control forces. Tab driven reversible pitch c ontrol designs m a y have insuffici ent authority to overcom e the elevator hinge m o ments resulting from ICTS. On som e airplanes, ICTS has been caused by a lateral flow com ponent com i ng from the vertical stabilizer, as m a y occur in sideslip conditions or due to a gust with a lateral com ponent.

b. Has ICTS occurred on airplanes? Following a num b er of acciden t s and inciden t s involving airplanes certificated unde r 14 CFR parts 23 and 2 5 for flight in icing cond itions, and specifically an accid e nt involving a British Aero space BA-3101 airp lane on Decem ber 26, 1989, the NTSB issued Safety Recommendation A-90-087.

c. What has been done to evaluate su sceptibility of airplanes to ICTS?

(1) In 1991, the FAA reviewed the pitch cont rol and stability f actors of various airp lanes to determ ine th e susceptibility of those airp lanes to ice con t am inated tailp la ne sta ll. The review included discussions with m a nufacturers of airplanes certificated for flight in known icing, analysis of stall margin design param e ters, and m e thods used to show com p liance with 14 CFR 23.143, Controllability and Man e uverab ility. Findings in cluded:

(a) Lack of clear understanding and unif o rm ity in applying the regulations due to

com p lexity of the issue.

(b) Need for unifor m and detailed guidance.

A7-1AC 23.1419-2D 4/19/07 Appendix 7

(c) Shortage of basic data on the subject.

(2) Before 1994, no uniform quantitative criteriaor standardized acceptan ce procedures were available to show com p liance with Title 14 CFR part 23, § 23.143 or its predecessor, CAR Part 3, § 3.106. In 1994, after exam ining available engineering data and its own guidance on this subject, the FAA decided to give m o re de tailed and uniform guidance on dem onstrating

com p liance. The FAA issued policy letters applic able to all airplanes and sponsored research with NASA to understand be tter ice contam inated tailplane stall. Based on the results of the data and guidance review, and with input from the joint FAA/NASA research project, the FAA determ ined that guidance would be helpful for two steps in the process lead ing to certification. The first step is the design phase when the prel im inary design param e ters of the airplane are determ ined. The second step is the m e thod of evaluation of compliance with the regulations.

(a) During the design process, the m a nufact urer can evaluate airplane response characteristics and efficiently resolv e seriou s problem s using various m odeling tools such as wind tunnel testing and com putati onal fluid dynam i cs analysis. This AC does not address this
process. (b) Susceptibility of an airplane design to ICTS should be considered when dem onstrating com p liance to the pitch control requirem e nts of CFR 23.143. The demonstration should include:

1. flight at the critical airsp eed;

2

. artificial ice accretions o n the horizo n tal tailplan e; and

3. flight testing in the critical trai ling edge flap and power configuration.

(3) In 2001, the FAA incorporated the 1 994 policy letters into AC 23.143-1, “Ice Contam inated Tailplane Stall. ”

(4) The guidance in AC 23.143-1 has been inco rporated into this AC and AC 23.143-1 has been can celled.

d. When can ICTS occur?

(1) Tailplane stall can occur with ice accretions on th e tailplan e when:

(a) wing flaps are extended;

(b) engine power is increased;

(c) the pilot m a kes a nose-down control input;

(d) the airplan e increases sp eed or encounters gust conditions; or

A7-24/19/07 AC 23.1419-2D Appendix 7

(e) a com b ination of these factors with flaps ex tended.

(2) Tailplane stall has been reported on seve ral airplane type designs with sm all quantities of ice observed on the airp lane. In so m e cases, the critical ice accretion fo r susceptibility to ICTS has been a thin rough layer of ice on the pr otected and unprotected portions of the lead ing edge th at accretes during the tim e that:

(a) The airplane enters icing conditions.

(b) The flightcrew recognizes the icing c onditions and activates the ice protection system

.
(c) The ice protection system pe rfor m s its intended function.

(3) Since flaps are norm a lly only extended to the landing position during final approach to land ing, an ICTS event under these conditions has a high p r obability of being catastrophic due to the associated low ground clearance

e. W h at are so m e pilot cues to ICTS? Pilots m a y sense ICTS or im pending ICTS as one or a

com b ination of :

(1) dif f i culty to trim in the p itch ax is;

(2) a pulsing or buffeting of th e longitudinal control; or

(3) a lightening of longitudinal control push force (or an increase in pull force ) necessary to command a new pitch attitude.

f. How does a pilot recover from ICTS? These m a y not be recognized as cues of ICTS. The pilot m a y incorrectly inte rpret these cues as aerodynam i c warning of an im pending wing stall and perfor m the wrong, possi bly catastrophic, corr ective action since r ecovery techniques for a wing stall are opposite those of an ICTS. It is critical for th e pilot to prom ptly and correctly diagnose the abnorm a l condition and apply the right correctiv e m easures, which typically are a pull up, flap retracti on, and power reduction.

2. FACTORS AFFECTING SUSCEP TIBILI TY OF AN AI RPLANE T O ICTS.

a. Airplane Design Variables. The aft location of th e tailplane relative to the wing, the lift generated by the wing, and the spanwise lift di stribution of the wing will affect the wing downwash induced tailplane AOA. Lift generated by wings with airfoils capable of high lift and equipped with efficient trailing edge flaps m a y induce a signifi cant increas e in the tailp l ane AOA. The airplane AOA, the wing downwash i nduced AOA, the tailplane fixed incidence angle, the tailplane design stall AOA, and the adverse effects of surface roughness on the tailplane stall AOA all influen ce the tailplane AOA m a rgin and susceptibility to stall.

A7-3AC 23.1419-2D 4/19/07 Appendix 7

b. Tail Design Variables.

(1) Vertical position of the horiz ontal tail and the aerodynam i c effects of the surfaces forward of the horizontal tail. (“T”, cruciform

, conventional).

(2) Fixed inc i d e nce ta ilp lan e with elevator and tr im tab.

(3) Variable Incidence Tailp lane (VIT ) with elev ato r

.
(4) All-m oving tailplane (stabila tor ) with and without a trim -servo tab.

(5) Characte r is tics of vertica l stab ilizer intera ction w ith T and c r ucif orm tails

.
(6) C LM ax , Coefficient of Maxim u m Li ft of wing and tailplane.

c. Center of Gravity (CG). Most forward CG loading conditio ns are usually m o st adverse to 1-g tailplane stall because of the greater balancing down load required by the tail. A greater download on the tail is developed by either increas ed incidence on a VIT, or grea ter tra iling edg e up deflection of the elevator.

d. Flap Extension. Extension of flaps increases the dow nwash at the tail and m oves the wing cente r of lif t af t, in cr easing nose-down pitching m o m e nt and requiring m o re tail download. In addition, the AOA of the airplane is re duced for the sam e lift. The tail is subje c ted to a negative increase in local AOA. The exte nsion of wing flaps, therefore, brings th e hor izonta l ta il closer to its stall AOA. Extendi ng flaps from the retracted pos ition m a y involve an increase in effective wing chord as well as an in creas e in camber. These changes in wing geometry :

(1) shif t the c e n t er of pressu re af t;

(2) increase the nose-down pitching m o m e nt;

(3) incre a se th e wing lif t coe f f i cient at th e sam e AOA; and

(4) like l y inc r ea se the local airf low downwas h angle aft of the flaps (even for T-tail configurations).

Because of these tes t s, m a xim u m landing flap extension m a y be defined at an in term ediate position which then m u st becom e an airplane lim ita tion for flights into icing conditions. In this instance, landing gear position warnings as a function of flap positi on and degraded landing perform a nce data should be considered.

e. Speed/Load Factor. In 1-g flight, higher airspeeds resu lt in reduced aircraft AOA an d a more negative tailplane AOA. For the sam e reas ons as described in paragraph 4 above, higher speed is m o re adverse to ICTS in 1-g fli ght. Also, during dynam i c m a neuvers (such as

A7-44/19/07 AC 23.1419-2D Appendix 7

pushovers), lower speeds put the tailplane at a mo re critical state (m or e negative AOA) due to the ability to generate higher pitch rates.

f. Engine Power. The effects of power or thrust on ICTS susceptibility are airplane specific. Increasing engine power on high thrust line aircraft (t hrust line above the C G ) requires more nose-up trim . This raises the risk of ICTS. In addition, in creasing engine power on propeller driven airplanes tends to be adverse to ICTS due to increas es in strength and angle of wing downwash, especially with flaps extended.

g. Maneuvering. There are two elem ents of m a neuveri ng that increase vulnerability to ICTS: nose-down pitch contro l input, and for som e configurations, sideslip.

(1) Nose-dow n pitch control input. When the elev ator is de flected to the nose-down position, horizontal tail cam b er is changed and ta il lift is reduced. Since a nose-down pitching

mom e nt exists tha t is no t com p letely balanced by the ta il, the airp lane will pitch nose-down and there will be angular rotation rate about the CG. The resultant aerodynamic effect on the horizon tal ta ilplane due to this ro ta tio n rate in the nose-down direction is an increased negative AOA which m a y increase susceptibility to tailplane stall.

(2) Side slip. O n “T” and cruciform tail configurat ions, local flow separation on the tailplane can star t with s i deslip du e to initiation of separation at the juncti on of the horizontal and vertical stabilizer. This conditi on is worsened by ice accretions on the vert ical stabilizer or structure forward of the horizon tal s t abilizer even if, in som e cases, th e h o rizon t al tail leading edge is uncontam i nated. The effects of a cont am i n ated vertical stab ilizer should also be considered when evaluating th e susceptib ility of a contam inated horizontal tailp lane to ICTS in a sideslip. On low tail configurations, im pi ngem e nt of flap tip vortices on the em pennage m a y result in elevator self deflecti on and lead to sim ilar control probl em s in the pitch axis. Sideslip can also result in asymm e tric conditions on the horiz ontal stabilizer due to prop wash effects. Airplanes w ithout counter-ro tating p r opellers p r o duce asymmetric local flow conditio ns. The steady heading sideslip should evaluate the eff ects of both lef t and right sideslip conditions.

h. Gusts and Turbulence. Gust or airplane gust response m a y contribute to ICTS. Gusts

m a y occur parallel to any airplane axis. The direct effect of a gust on the resultant airflow

m a y be adve rse. The flight tests should be r obust enough to evaluate the characteristics of the tail for various com b inations of conditions.

A7-5 (and A7-6)4/19/07 AC 23.1419-2D Appendix 8

APPE NDI X 8. AFM LIMITATI ONS AND NORMAL PROCEDURES S E CT IONS

1. LIMITATI ONS SECTION. The following text and warning inform ation should be inser t ed in the lim itation s section of the AFM:

a. Flight in m e teoro l ogical conditions d e scrib e d as f r eezing rain or freezing d r izzle, as determ ined by the f o llo wing visual cues, is p r oh ibited:

(1) Unusually extensiv e ice accreted on the airfram e in areas no t n o rm ally observed to collect ice.

(2) Accum u lation of ice on the upper su rface or low e r surface of the wing aft of the protected area.

(3) Accum u lation of ice on the propeller spi nner farther back than norm a lly observed.

If the airplane encounters conditions that ar e determ ined to contain freezing rain or freezing drizzle, th e pilo t m u st imm e diately exit the freezing rain or freezing drizzle conditions by changing altitude or course.

NOTE 7: The prohib ition on flight in fr eezing rain or freezing drizzle is not intended to prohibit purely inadverten t encoun ters with th e s p ecified

m e teorological cond itio ns; however, pilots should m a ke all reasonable efforts to avoid such encounters and m u st immediat ely exit the conditio ns if they are encountered.

b. Use of the autopilot is prohibited when any ice is observed form ing aft of the protected su rfaces of the wing, or when unusual lateral trim requirem e nts or autop ilot trim warnings are encountered.

NOTE 8: The autopilot m a y mask tactil e cues th at ind i cate adverse ch an ges in handling characteristics; therefore, the pilot should consider not using the autopilot wh en any ice is visible on the airplane.

c. All wing ice inspection lights m u st be operab l e p r ior to flight in to known or forecast icing at night.

NOTE 9: This supersedes any relie f provided by the Master Minim u m Equipm ent List (MMEL).”

2. NORMAL PROCEDURES S E CT ION. The following text and warning inform ation should be inserted in the norm a l procedures section of the AFM:

A8-1AC 23.1419-2D 4/19/07 Appendix 8

WARNI NG



## • If ice is obs erved form ing aft of the protected su rfaces of the wing or if unusual lateral trim requirem e nts or autopilot trim warnings are encountered, accom p lish the following:



## • If the flaps are extended, do not re tra c t them until the airf ram e is clear of ice.



## • The flight crew should reduce th e angle-of-attack by increasing speed as m u ch as the airplane configuration and weather allo w, without exceeding design m a neuvering speed.



## • If the autopilot is engaged, hol d the control wheel firm ly and disengage the autopilot. Do not re-en g age the au topilot un til the airfram e is clear of ice.



## • Exit the icin g area imm e diate l y by changing altitude or course; and



## • Report the s e weather con d itions to a i r traf f i c contr o l.

CAUTION
Flight in freezing rain or freezing drizzle, m a y result in h azardous ice build-up on protec ted surfaces ex ceeding the capability of the ice protection system , or m a y result in ice form ing aft of the protected su rfaces. This ice m a y not be shed using the ice protection system s, and it m a y seriously degrade the perform a nce and controllability of the airplane.

a. The following shall b e u s ed to id entify fr eezing rain/freezing driz zle icing conditions:

(1) Unusually extensiv e ice accreted on the airfram e in areas no t n o rm ally observed to collect ice.

(2) Accum u lation of ice on the upper su rface or low e r surface of the wing aft of the protected area.

(3) Accum u lation of ice on the propeller spinne r farther back than norm a lly observed.

b. The following m a y be used to id entify possible freez ing ra in/freezing driz zle cond itio ns:

(1) Visible rain at tem p eratu r es below plus five degrees C OAT.

(2) Droplets that splash o r spla tter on impact at tem p eratu r es below plus five degrees C OAT.

A8-24/19/07 AC 23.1419-2D Appendix 8

(3) Perform a nce losses larger than norm a lly encountered in icing conditions. It is possible to experience seve re ice accretions not vi sible to the f light crew, such as wing lower surface accretion on a lo w wing airplane or prop eller blade accretion.

c. Procedures for Exiting the Freez ing Rain/Freez i ng Dri z z l e Environment. These procedures are applicable to all flight phases from takeoff to landing. Monitor the outside air
tem p erature. W h ile ice m a y for m in freezing drizzle o r freez ing rain at temperatures as cold as

m i nus 18 de grees C, increased vig ilance is wa rranted at tem p eratu r es aro und freezing with visible m o isture present. If the visua l cues spe c if ied in th e AFM for identifying possible freezing rain or freezing drizzle conditions are observed, accom p lish the following :

(1) Exit the fre e z ing ra in or freezing driz zl e icing con d itions immediately to a void extended exposure to flight conditions outside of those for which the airplane has been certificated for operation. Asking for priority to leave the area is fu lly justif ied under these conditions.

(2) Avoid abrup t and excessive m a neuvering th at m a y exacerb a te contro l difficulties.

(3) Do not engage the autopilot. The autop ilot m a y m a sk unusual control system forces

(4) If the autopilot is engaged, hold the control wheel firm ly and disengage the autopilot.

(5) If an unusual roll response or uncomm a nded control m ove m e nt is observed, reduce the angle-of-attack by in creas ing airs peed or ro lling wings level (if in a turn), and apply additional power, if needed.

(6) Avoid extending flaps during extended ope ration in icing conditions. Operation with flaps extended can result in a reduced wi ng angle-of-attack, with ice for m ing on the upper surface furth e r aft on the wing than n o rm al , possibly aft of the protected area.

(7) If the flaps are extended, do not retract th em until the airfram e is clear of ice.

(8) Report these weather conditions to A T C.

NOTE 10: An alternate m eans of provi ding th is inf o rm ation in the AFM m a y be approved by the certif ying agency

.

A8-3 (and A8-4)