Vol. 79 Tuesday, 

No. 213 November 4, 2014 

Part III 

Department of Transportation 

Federal Aviation Administration 

14 CFR Parts 25 and 33 

Airplane and Engine Certification Requirements in Supercooled Large Drop, 

Mixed Phase, and Ice Crystal Icing Conditions; Final Rule 


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65508 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Parts 25 and 33 

[Docket No. FAA–2010–0636; Amendment 

Nos. 25–140 and 33–34] 

RIN 2120–AJ34 

Airplane and Engine Certification 

Requirements in Supercooled Large 

Drop, Mixed Phase, and Ice Crystal 

Icing Conditions 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Final rule. 

SUMMARY: The Federal Aviation 

Administration is amending the 

airworthiness standards applicable to 

certain transport category airplanes 

certified for flight in icing conditions 

and the icing airworthiness standards 

applicable to certain aircraft engines. 

The regulations will improve safety by 

addressing supercooled large drop icing 

conditions for transport category 

airplanes most affected by these icing 

conditions; mixed phase and ice crystal 

conditions for all transport category 

airplanes; and supercooled large drop, 

mixed phase, and ice crystal icing 

conditions for all turbojet, turbofan, and 

turboprop engines. 

DATES: Effective January 5, 2015. 

ADDRESSES: For information on where to 

obtain copies of rulemaking documents 

and other information related to this 

final rule, see ‘‘How To Obtain 

Additional Information’’ in the 

SUPPLEMENTARY INFORMATION section of 

this document. 

FOR FURTHER INFORMATION CONTACT: For 

part 25 technical questions contact 

Robert Hettman, FAA, Propulsion/

Mechanical Systems Branch, ANM–112, 

Transport Airplane Directorate, Aircraft 

Certification Service, 1601 Lind Avenue 

SW., Renton, WA 98057–3356; 

telephone (425) 227–2683; facsimile 

(425) 227–1320; email robert.hettman@

faa.gov. 

For part 33 technical questions 

contact John Fisher, FAA, Rulemaking 

and Policy Branch, ANE–111, Engine 

and Propeller Directorate Standards 

Staff, Aircraft Certification Service, 12 

New England Executive Park, 

Burlington, MA 01803; telephone (781) 

238–7149; facsimile (781) 238–7199; 

email john.fisher@faa.gov. 

For part 25 legal questions contact 

Douglas Anderson, FAA, Office of the 

Regional Counsel, ANM–7, Northwest 

Mountain Region, 1601 Lind Avenue 

SW., Renton, WA 98057–3356; 

telephone (425) 227–2166; facsimile 

(425) 227–1007; email 

douglas.anderson@faa.gov. 

For part 33 legal questions contact 

Vince Bennett, FAA, Office of the 

Regional Counsel, ANE–007, New 

England Region, 12 New England 

Executive Park, Burlington, MA 01803; 

telephone (781) 238–7044; facsimile 

(781) 238–7055; email vincent.bennett@

faa.gov. 

SUPPLEMENTARY INFORMATION: 

Authority for This Rulemaking 

The FAA’s authority to issue rules on 

aviation safety is found in Title 49 of the 

United States Code. Subtitle I, Section 

106 describes the authority of the FAA 

Administrator. Subtitle VII, Aviation 

Programs, describes in more detail the 

scope of the agency’s authority. 

This rulemaking is under the 

authority described in Subtitle VII, Part 

A, Subpart III, Section 44701, ‘‘General 

requirements.’’ Under that section, the 

FAA is charged with promoting safe 

flight of civil aircraft in air commerce by 

prescribing minimum standards 

required in the interest of safety for the 

design and performance of aircraft; 

regulations and minimum standards in 

the interest of safety for inspecting, 

servicing, and overhauling aircraft; and 

regulations for other practices, methods, 

and procedures the Administrator finds 

necessary for safety in air commerce. 

This regulation is within the scope of 

that authority because it prescribes— 

• New safety standards for the design 

and performance of certain transport 

category airplanes and aircraft engines; 

and 

• New safety requirements necessary 

for the design, production, and 

operation of those airplanes, and for 

other practices, methods, and 

procedures relating to those airplanes 

and engines. 

Overview of Final Rule 

The FAA is adopting this final rule to 

revise certain regulations in Title 14, 

Code of Federal Regulations (14 CFR) 

part 25 (Airworthiness Standards: 

Transport Category Airplanes) and part 

33 (Airworthiness Standards: Aircraft 

Engines) related to the certification of 

transport category airplanes and turbine 

airplane engines in icing conditions. We 

are also creating the following new 

regulations: § 25.1324—Angle of attack 

systems; § 25.1420—Supercooled Large 

Drop Icing Conditions; Appendix O to 

Part 25—Supercooled Large Drop Icing 

Conditions; Appendix C to Part 33 (this 

is intentionally left blank as a 

placeholder for potential future 

rulemaking unrelated to icing); and 

Appendix D to Part 33 Mixed Phase and 

Ice Crystal Icing Envelope (Deep 

Convective Clouds). To improve the 

safety of transport category airplanes 

operating in supercooled large drop 

(SLD), mixed phase, and ice crystal 

icing conditions, these regulations will: 

• Require airplanes most affected by 

SLD icing conditions to meet certain 

safety standards in an expanded 

certification icing environment that 

includes freezing drizzle and freezing 

rain. These safety standards include 

airplane performance and handling 

qualities requirements. 

• Expand the engine and engine 

installation certification, and some 

airplane component certification 

regulations (for example, angle of attack 

and airspeed indicating systems) to 

include freezing drizzle, freezing rain, 

mixed phase, and ice crystal icing 

conditions. 

Summary of the Costs and Benefits of 

the Final Rule 

The benefits and costs are 

summarized in the table below. As 

shown in the table, the total estimated 

benefits exceed the total estimated costs 

for this final rule. 

2012$ 7% Present value 

Benefit Cost Benefit Cost 

Part 33 Engines ............................................................................. Qualitative ......... $13,936,000 Qualitative ........ $11,375,927 

Large Part 25 Airplanes ................................................................. $362,319,857 ... 14,126,333 $76,861,295 ..... $11,531,295 

Other Part 25 Airplanes ................................................................. $220,570,582 ... 33,198,788 $50,028,690 ..... $19,385,401 

Total ........................................................................................ $582,890,439 ... 61,261,121 $126,889,985 ... $42,292,624 


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1NTSB Safety Recommendations A–96–54 and 

A–96–56 are available in the rule Docket No. FAA– 

2010–0636 and on the Internet at http://

www.ntsb.gov/doclib/recletters/1996/A96_48_

69.pdf. 

2Published in the Federal Register on December 

8, 1997 (62 FR 64621). http://www.gpo.gov/fdsys/

pkg/FR-1997-12-08/pdf/97-32034.pdf. 

3Part 25 Activation of Ice Protection, Docket No. 

FAA–2007–27654, published in the Federal 

Register on August 3, 2009 (74 FR 38328). Part 121 

Activation of Ice Protection, Docket No. FAA–2009– 

0675, published in the Federal Register on August 

22, 2011 (76 FR 52241). 

Background 

Safety concerns about the adequacy of 

the icing certification standards were 

brought to the forefront of public and 

governmental attention by a 1994 

accident in Roselawn, Indiana, 

involving an Avions de Transport 

Re ́gional (ATR) ATR 72 series airplane. 

The National Transportation Safety 

Board (NTSB), with assistance from 

ATR, the FAA, the French Direction 

Ge ́ne ́ral de l’Aviation Civile, Bureau 

D’Enquetes et D’Analyses, the National 

Aeronautics and Space Administration 

(NASA), and others, conducted an 

extensive investigation of this accident. 

This investigation determined that 

freezing drizzle-sized drops created a 

ridge of ice on the wing’s upper surface 

aft of the deicing boots and forward of 

the ailerons. The investigation further 

concluded that this ridge of ice 

contributed to an uncommanded roll of 

the airplane. Based on these findings, 

the NTSB recommended changes to the 

icing certification requirements. 

The atmospheric icing conditions for 

certification are specified in part 25, 

appendix C. The atmospheric condition 

(freezing drizzle) that contributed to the 

Roselawn accident is outside the icing 

envelope currently used for certifying 

transport category airplanes. The term 

‘‘icing envelope’’ is used in part 25, 

appendix C, and in this rule to refer to 

the environmental icing conditions 

within which the airplane must be 

shown to be able to safely operate. The 

term ‘‘transport category airplanes’’ is 

used throughout this rulemaking 

document to include all airplanes typecertificated to part 25 regulations. 

Another atmospheric icing 

environment outside the current icing 

envelope is freezing rain. The FAA has 

not required airplane manufacturers to 

show that airplanes can operate safely 

in a freezing drizzle or freezing rain 

icing environment. 

As a result of this accident and 

consistent with related NTSB 

recommendations,1 the FAA tasked the 

Aviation Rulemaking Advisory 

Committee (ARAC),2 through its Ice 

Protection Harmonization Working 

Group (IPHWG), to do the following: 

• Define an icing environment that 

includes SLD conditions. 

• Consider the need to define a mixed 

phase icing environment (supercooled 

liquid and ice crystals). 

• Devise requirements to assess the 

ability of an airplane to either safely 

operate without restrictions in SLD and 

mixed phase conditions or safely 

operate until it can exit these 

conditions. 

• Study the effects icing requirement 

changes could have on §§ 25.773, Pilot 

compartment view; 25.1323, Airspeed 

indicating system; and 25.1325, Static 

pressure systems. 

• Consider the need for a regulation 

on ice protection for angle of attack 

probes. 

The FAA ultimately determined that 

the revised icing certification standards 

should include SLD, mixed phase, and 

ice crystal icing conditions. This rule is 

based on ARAC’s recommendations to 

the FAA. 

A. Related Actions 

ARAC’s IPHWG submitted additional 

icing rulemaking recommendations to 

the FAA that led to the Part 25 and Part 

121 Activation of Ice Protection final 

rules.3 For certain airplanes certificated 

for flight in icing, those rulemaking 

actions revise the certification and 

operating rules for flight in icing 

conditions by requiring either 

installation of ice detection equipment 

or changes to the airplane flight manual 

(AFM) to ensure timely activation of the 

airframe ice protection system. 

Although those rulemaking actions 

address flight in icing conditions, they 

do not directly impact this final rule. 

B. NTSB Recommendations 

The NTSB issued NTSB Safety 

Recommendation Numbers A–96–54 

and A–96–56 as a result of the Roselawn 

accident previously discussed. This 

rulemaking partially addresses those 

NTSB recommendations. The FAA is 

considering separate rulemaking 

activities associated with revisions to 14 

CFR part 23 regulations for small 

airplanes and 14 CFR part 121 

operational regulations to complete the 

FAA response to these NTSB 

recommendations. The NTSB 

recommendations are as follows: 

1. A–96–54 

Revise the icing criteria published in 

14 CFR parts 23 and 25, in light of both 

recent research into aircraft ice 

accretion under varying conditions of 

liquid water content (LWC), drop size 

distribution, and temperature, and 

recent developments in both the design 

and use of aircraft. Also, expand the 

appendix C icing certification envelope 

to include freezing drizzle/freezing rain 

and mixed water/ice crystal conditions, 

as necessary (A–96–54 supersedes A– 

81–116 and –118). 

2. A–96–56 

Revise the icing certification testing 

regulation to ensure that airplanes are 

properly tested for all conditions in 

which they are authorized to operate, or 

are otherwise shown to be capable of 

safe flight into such conditions. If safe 

operations cannot be demonstrated by 

the manufacturer, operational 

limitations should be imposed to 

prohibit flight in such conditions, and 

flightcrews should be provided with the 

means to positively determine when 

they are in icing conditions that exceed 

the limits for aircraft certification. 

C. Summary of the Notice of Proposed 

Rulemaking 

The notice of proposed rulemaking 

(NPRM), Notice No. 10–10, published in 

the Federal Register on June 29, 2010 

(75 FR 37311), is the basis for this final 

rule. After receiving several requests to 

extend the public comment period, the 

FAA extended the comment period by 

30 days to September 29, 2010, with a 

document published in the Federal 

Register on August 16, 2010 (75 FR 

49865). 

To improve the safety of transport 

category airplanes operating in SLD, 

mixed phase, and ice crystal icing 

conditions, the FAA proposed new 

regulations in the NPRM to: 

• Expand the certification icing 

environment to include freezing drizzle 

and freezing rain environments. 

• Require airplanes most affected by 

SLD icing conditions to meet certain 

safety standards in the expanded 

certification icing environment, 

including airplane performance and 

handling qualities requirements. 

• Expand the engine and engine 

installation certification regulations, 

and some airplane component 

certification regulations (for example, 

angle of attack and airspeed indicating 

systems), to include freezing rain 

environments, freezing drizzle 

environments, mixed phase, and ice 

crystal icing conditions. For certain 

regulations, we proposed using a subset 

of these icing conditions. 

D. General Overview of Comments 

The FAA received comments from 31 

commenters during the public comment 

period: Five private citizens, the 

Aerospace Industries Association (AIA), 

Airbus Industrie (Airbus), AirDat LLC, 

the Airline Pilots Association (ALPA), 


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American Kestrel Company, LLC, 

(AKC), The Boeing Company, 

Bombardier, Cessna, Dassault Aviation, 

Embraer, Eurocopter, the European 

Aviation Safety Agency (EASA), Foster 

Technology, LLC, the General Aviation 

Manufacturers Association (GAMA), GE 

Aviation, Gulfstream, Goodrich Sensors 

and Integrated Systems (GSIS), 

Honeywell Engines, the National 

Research Council (NRC), the NTSB, 

Pratt & Whitney Canada, the Regional 

Airline Association (RAA), the Swiss 

Federal Office of Civil Aviation (FOCA), 

Snecma, Transport Canada Civil 

Aviation (TCCA), and Turbomeca. Each 

commenter submitted multiple 

comments. 

Twelve commenters stated specific 

support for the rulemaking, recognized 

the efforts made by the ARAC working 

group, and suggested specific changes 

intended to clarify the regulations or to 

clarify the intent. The NTSB and two 

private citizens were disappointed that 

the rulemaking took so long. 

Fourteen commenters stated neither 

support nor opposition, but suggested 

specific changes or identified areas for 

clarification. 

Two commenters, a rotorcraft 

manufacturer and a rotorcraft engine 

manufacturer, opposed the proposed 

changes to §§ 33.68 and 33.77. These 

commenters suggested the FAA make 

provisions to exclude rotorcraft from the 

revised regulations. 

Two private citizens expressed 

concern for the data and methods used 

to define the SLD conditions proposed 

in part 25, appendix O. 

One commenter suggested that the 

FAA should begin a certification 

process toward use of a new 

methodology for detecting ice over a 

pitot inlet, for which the commenter has 

filed a provisional patent. 

The FAA received additional 

comments in a letter dated June 21, 

2011, signed by four private citizens. 

The letter provided additional 

explanation for previously submitted 

comments. The FAA also considered 

this additional information while 

drafting this final rule. 

The FAA made changes to the final 

rule in response to the public 

comments. Summaries of the issues 

raised by the public comments and FAA 

responses, including explanations of 

changes, are provided below. The full 

text of each commenter’s submission is 

available in the docket for this 

rulemaking. 

Discussion of Public Comments and 

Final Rule 

Proposed Appendix O to Part 25 

In the NPRM, the FAA proposed to 

expand the existing icing conditions 

identified in appendix C of part 25 to 

include new SLD icing conditions 

defined in a new appendix O. The FAA 

made changes to appendix O as a result 

of comments received, but the general 

format remains unchanged. Appendix O 

is structured like part 25, appendix C, 

with part I defining icing conditions and 

part II defining airframe ice accretions 

for showing compliance with the 

airplane performance and handling 

qualities requirements of part 25, 

subpart B. 

Three private citizens provided 

comments related to the flight data 

collection approach used to acquire 

information about SLDs, the flight data 

used, and the analysis approach to 

generate the SLD engineering standards 

in part 25, appendix O. We will address 

these three commenters as a group. 

One concern was with the methods 

related to collecting and evaluating SLD 

icing conditions. One commenter stated 

that the research aircraft were well 

equipped to document the environment; 

however, both research aircraft had 

serious deficiencies regarding their onboard ability to document aircraft 

performance degradation from icing. 

Two commenters were concerned that 

only the database jointly created by 

Environment Canada and NASA was 

used to define the SLD icing conditions. 

Another commenter was concerned 

about the statistical significance of the 

data collected and did not think there 

was enough flight test evidence 

collected to provide the same level of 

probability established for part 25, 

appendix C, icing conditions. Two 

commenters stated that the flight test 

campaign failed to relate their data 

collection results to previously 

published results, such as those 

published by the University of 

Wyoming. Specifically, the commenters 

noted that appendix O does not contain 

data for a LWC greater than 0.45 grams 

per cubic meter. 

One commenter also stated that other 

published analysis methods for an SLD 

encounter, such as the University of 

Wyoming LWC/drop size technique, 

result in the most adverse icing 

conditions and are not contained within 

appendix O. The commenter also noted 

that a clear distinction does not exist 

between the icing conditions defined in 

part 25, appendix C, and the conditions 

defined in part 25, appendix O. This 

uncertainty would leave the pilot with 

the responsibility of making a scientific 

finding of which icing conditions the 

airplane was in, unless on-board droplet 

size and LWC measurement means and 

droplet data processing are provided. 

Regarding the flight research project’s 

lack of on-board ability to document 

aircraft performance degradation from 

icing, we agree. However, obtaining 

measurements of aircraft performance 

within icing conditions was the lowest 

priority objective of the flight research 

project. The primary objectives of the 

test were to identify icing conditions 

beyond those covered in appendix C of 

part 25, and to identify a method for 

presenting the data in a way that could 

be used as an engineering standard. 

Specific aircraft performance and 

handling degradations in icing 

conditions are unique for each aircraft 

design. Performance degradation and 

handling qualities criteria for appendix 

C and appendix O icing encounters will 

need to be determined by the design 

approval holder for each aircraft design 

based on the applicable regulations, 

guidance materials, and testing as 

necessary to demonstrate compliance. 

This final rule specifies the expanded 

environmental icing conditions for 

consideration during the certification 

process as well as the performance and 

handling qualities that must be 

demonstrated. 

Regarding the sufficiency of the flight 

test data to form a statistically reliable 

database, we disagree. In developing 

appendix O, we used all historically 

available flight research data on SLD, 

not just the Environment Canada-NASA 

flight test data. This broad collection of 

data is statistically similar to the data 

that was used to develop appendix C. 

Regarding the comments about our 

proposed definition of SLD in appendix 

O, we also disagree. The University of 

Wyoming data were included in the 

FAA master database on SLD icing 

conditions. However, these data were 

not used to support the final 

determinations for the LWC values for 

the appendix O engineering standards. 

The University of Wyoming aircraft was 

not equipped with two-dimensional 

optical array probes, which were 

deemed essential by the IPHWG. 

Without the probes, it was not possible 

to distinguish between cloud drops and 

ice particles. Therefore, the University 

of Wyoming cloud data were not 

considered usable for supporting the 

analysis of SLD LWC/drop size 

properties for appendix O. As a result, 

the Environment Canada-NASA 

database was used to determine the 

engineering standards because of the 

quality of the data contained therein 

and the analysis methods used in that 

database. Both the quality of the data 


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4The data used to complete the IPHWG report is 

detailed in report DOT/FAA/AR–09/10, Data and 

Analysis for the Development of an Engineering 

Standard for Supercooled Large Drop Conditions, 

dated March 2009. A copy of the report is available 

in the rule Docket No. FAA–2010–0636. The data 

used for figure 7 are described on pages 34–39 of 

that report. 

5A copy of the report is in the rule Docket No. 

FAA–2010–0636. 

6National Advisory Committee for Aeronautics 

Technical Note 2738, A Probability Analysis of the 

Factors Conducive to Aircraft Icing in the United 

States, by William Lewis and Norman R. Bergrun, 

July 1952. 

and the analysis method used by the 

database ensured the accuracy of the 

definition for appendix O icing 

conditions. 

Regarding the comment that the 

University of Wyoming LWC/drop size 

technique results in the most adverse 

icing conditions and are not contained 

within appendix O, we disagree. That 

analysis technique suggests that one 

type of icing condition would be severe 

for all airplanes, regardless of the type 

of ice protection system used, or the 

extent of the protection. Appendix O 

contains a variety of icing conditions, 

not just those deemed most severe using 

the University of Wyoming analysis 

technique. 

In response to other comments, 

figures 1 and 4 of appendix O have been 

revised in this final rule to reflect the 

LWC proposed by the IPHWG. As a 

result, freezing drizzle conditions with 

a median volume diameter (MVD) 

greater than 40 microns fall within the 

adverse region that would be identified 

using the University of Wyoming LWC/ 

drop size technique. No changes to 

appendix O were made as a result of 

these comments. 

With regard to the comment 

suggesting that the pilot will have to 

make a scientific finding to determine 

which icing conditions the airplane is 

in, we disagree. For those types of 

airplanes most vulnerable to SLD icing 

conditions, the level of operations in 

SLD icing conditions for which the 

airplane is approved will be determined 

during the airplane certification process 

in accordance with § 25.1420. If 

approval is requested for operations in 

a portion of the icing conditions defined 

in appendix O, then the airplane 

manufacturer will have to show that the 

pilot can determine if the operational 

envelope for which the airplane is 

certified has been exceeded as required 

by § 25.1420(a)(2). Since part of the 

certification will be evaluating the 

means used to distinguish when the 

airplane is in icing conditions outside 

the certified envelope, the pilot will not 

be faced with the ambiguity of trying to 

determine the distribution of water 

drops in the environment in which he 

or she is flying. 

Several commenters said that 

proposed figures 1, 4, and 7 in appendix 

O of the NPRM were different than what 

was proposed by the IPHWG, and that 

the FAA did not provide an explanation 

for those differences. The commenters 

also noted that the higher LWC 

contained in the figures proposed in the 

NPRM could have a significant impact 

on an applicant’s design. GSIS 

specifically noted that the higher water 

content defined in appendix O will have 

the effect of greatly increasing power 

requirements for electro-thermal deicing 

systems. Several commenters also 

suggested that figures 1, 3, 4, and 6 of 

appendix O would be easier to use if the 

corner data points were defined in the 

figures. 

We agree. We reviewed the figures 

proposed in the NPRM and the data 

used by the IPHWG to generate the 

figures. We revised figures 1 and 4 to 

reflect the lower water content values 

proposed by the IPHWG, but the water 

content in appendix O is still higher 

than within appendix C at the same 

temperature. The higher water content 

may increase the power requirements 

for some electro-thermal deicing system 

designs, but not to the extent that may 

have been necessary with the water 

contents proposed in the NPRM. The 

environmental conditions defined in 

appendix O are valid conditions that 

will need to be considered for 

applicable future designs. Our review of 

the data used to generate the scaling 

factor curve in figure 7 indicates that the 

figure 7 proposed by the IPHWG in the 

task 2 working group report was 

incorrect; 4 figure 7 in the NPRM was 

correct. Therefore, figure 7 in this final 

rule remains as proposed in the NPRM. 

Figures 1, 3, 4, and 6 of appendix O in 

this final rule have been revised to 

identify the corner data points for 

clarity. 

GSIS asked if there is a scientific basis 

for applying the horizontal extent of 

17.4 nautical miles. GSIS also noted that 

the same MVD, temperature, and LWC 

at altitude exist in both appendix O and 

appendix C and asked the FAA to 

clearly define the mass distribution 

boundary between appendix O and 

appendix C. 

Our application of the 17.4 nautical 

mile horizontal extent in appendix O 

was made on a practical basis and not 

on a purely scientific basis; it was 

selected for consistency with the 

appendix C continuous maximum icing 

conditions with which designers are 

already familiar. We are unaware of any 

scientific reasons for not applying the 

17.4 nautical mile horizontal extent in 

this manner. 

The LWC values in appendix O are 

based on an analysis of the data from 

the jointly created Environment CanadaNASA flight research SLD database, 

report DOT/FAA/AR–09/10.5 Figure 11 

of that report shows a plot of 

temperature versus LWC for appendix O 

freezing drizzle environments that is 

valid for the reference distance of 17.4 

nautical miles (32.2 km). Appendix C 

and appendix O define environmental 

conditions that overlap one another as 

the conditions transition from appendix 

C to appendix O. Therefore, there is not 

a clear mass distribution boundary that 

can be defined. 

One commenter, a private citizen, 

noted that the NPRM did not identify 

the vertical extent for part 25, appendix 

O, figure 6. We disagree. The pressure 

altitude range and vertical extent for 

freezing rain were provided in appendix 

O, part I, paragraph (b) in the NPRM 

located under figure 3. We clarified 

appendix O, part I, by moving all of the 

general text describing the 

meteorological parameters, including 

vertical extent, ahead of the figures. 

One commenter suggested that the 

icing conditions in appendix O should 

be revised to reflect water drop 

distribution as a function of mean 

effective diameter (MED) as opposed to 

MVD. We do not agree. MED is the term 

used in part 25, appendix C. 

Examination of National Advisory 

Committee for Aeronautics (NACA) 

references 6 shows that MED is the same 

as MVD if certain assumptions are made 

about the drop distribution, namely that 

it is one of the Langmuir distributions. 

MVD, as the more general term, is 

applicable to any drop distribution. 

Since the drop distribution described in 

appendix O does not follow a Langmuir 

distribution, MVD is more appropriate. 

We did not change the final rule or 

appendix O as a result of this comment. 

A private citizen commented that 

appendix O should define a time to use 

for delayed recognition of entry into 

icing conditions and the time to exit 

icing conditions. We do not agree. The 

responsibility for proposing delayed 

recognition times, delayed ice 

protection system activation times, or 

times required to exit icing conditions, 

based on unique operational procedures 

or performance characteristics of the ice 

protection system, rests with the 

applicant. We did not change the rule 

based on this comment. 

Boeing suggested a change to 

appendix O, part I, paragraph (c), to add 

an equation to determine the LWC for 


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horizontal distances other than 17.4 

nautical miles. 

We agree that adding such an 

equation could be beneficial. The 

equation proposed by Boeing, however, 

expressed horizontal distance in 

kilometers, which would be 

inconsistent with other figures in 

appendix O. Instead of the equation 

proposed by Boeing, we added to 

appendix O, part I, paragraph (c), a 

similar equation that uses units of 

nautical miles. 

Several commenters noted that 

appendix O, part II, paragraph (b)(5)(ii), 

in the NPRM made reference to 

§§ 25.143(k) and 25.207(k). However, 

§§ 25.143(k) and 25.207(k) do not exist 

in the current part 25 and were not 

added by the NPRM. 

We agree. The references to those 

sections were inadvertently included in 

the NPRM. We revised appendix O to 

delete the statement referencing 

§§ 25.143(k) and 25.207(k). 

Airbus noted that part II, paragraph 

(c)(7)(v) of appendix O states that crew 

activation of the ice protection system is 

in accordance with a normal operating 

procedure provided in the AFM, except 

that after beginning the takeoff roll, it 

must be assumed that the crew does not 

take any action to activate the ice 

protection system until the airplane is at 

least 400 feet above the takeoff surface. 

Airbus commented that this appears to 

be a direct cut and paste from the 

appendix C regulations and 

recommended removing the sentence. 

Airbus claimed that while this is 

perhaps understandable for appendix C 

icing conditions, it would seem 

reasonable to expect the crew to activate 

the wing anti-ice system (WAIS) prior to 

takeoff if there are SLD icing conditions 

within 400 feet of the runway, whether 

the AFM specifically states that it is 

required or not. 

We do not agree. The rule addresses 

flightcrew actions occurring after 

beginning the takeoff roll, while Airbus’ 

comment refers to actions that the 

flightcrew would take before beginning 

the takeoff. Nevertheless, the FAA does 

not expect flightcrews to be aware of all 

SLD icing conditions that may exist up 

to a height of 400 feet above the takeoff 

surface, nor do we agree that it would 

be reasonable to expect the flightcrew to 

activate the WAIS prior to takeoff if 

there was no procedure telling them to 

do so. We did not change the rule based 

on this comment. 

Embraer commented that the last 

sentence in appendix O, part II, 

paragraph (b)(2)(ii), which proposed to 

define the holding ice conditions in part 

25, appendix O, part II, paragraph (b)(2), 

should be applicable to the whole of 

paragraph (b)(2), and not just to the 

transit time through one appendix O 

cloud and one appendix C cloud 

specified in paragraph (b)(2)(ii). 

Embraer commented that it would be 

clearer to describe the total holding time 

in a separate paragraph (b)(2)(iii) that 

says: ‘‘The total exposure to the icing 

conditions need not exceed 45 

minutes.’’ We agree, and changed 

appendix O, part II, paragraph (b)(2), to 

indicate that the total exposure time for 

holding ice does not need to exceed 45 

minutes. 

Availability of Engineering Tools To 

Show Compliance With the Rule 

Several commenters stated that 

available engineering tools (icing wind 

tunnels and tankers, ice accretion 

prediction codes, and other analysis 

methods) are inadequate for showing 

compliance with the new rule. 

Bombardier commented that without 

validated tools, it is not practical to 

implement the requirements proposed 

in the NPRM. Bombardier believed that 

efforts should be focused on 

implementing incremental regulatory 

changes in parallel with the appropriate 

technological developments to meet that 

regulatory change. 

Boeing commented similarly, stating 

that the FAA and NASA had developed 

a plan several years ago to align the 

timing of the new regulations with the 

availability of validated engineering 

tools and test capabilities for SLD 

conditions. Boeing added that the tools 

and test facilities necessary to 

effectively demonstrate compliance 

with the regulations are not available, 

and that this lack of availability will be 

particularly problematic for applicants 

desiring to operate within appendix O 

conditions. Boeing noted that the 

current situation will require applicants 

to either use highly conservative 

approaches, build new icing wind 

tunnel facilities, or expend great efforts 

to conduct extensive flight testing in 

search of a meteorological condition, 

which occurs very infrequently. Boeing 

said that this was not the approach 

anticipated by industry, and that it will 

impose a severe burden on many 

applicants beyond that established in 

the economic evaluation of the 

proposed regulation, without adding 

any commensurate safety benefit. 

AKC also commented that current test 

facilities are limited in their ability to 

produce freezing drizzle, in particular 

drop distributions greater than 40 

microns MVD. The water drop 

distribution curves provided in 

appendix O are not produced by any 

facility known to AKC, and there are no 

facilities that produce freezing rain in a 

fashion that duplicates either the flight 

or ground test environment. 

The NRC of Canada’s comments 

reflected concerns about how the water 

drop distribution curves in appendix O 

are to be used. Further, a private citizen 

commented that the droplet diameters 

for appendix O conditions can only be 

reproduced in a few icing wind tunnels. 

We do not agree that available 

engineering tools (icing wind tunnels 

and tankers, ice accretion prediction 

codes, and other analysis methods) are 

inadequate for showing compliance 

with the new rule. We recognize that the 

current engineering tools available to 

show compliance with the new SLD 

rule have not been validated in every 

aspect, and also have some limitations. 

We also recognize that for freezing rain, 

few validated engineering tools are 

available. However, methods are 

available to simulate freezing drizzle. 

Further, we recognize that relying upon 

available simulation methods, combined 

with engineering judgment, will be 

required for finding compliance with 

the appendix O requirements of part 25, 

especially for freezing rain conditions. 

After reviewing the current state of 

available compliance methods and 

engineering tools, the FAA has 

determined that there is sufficient 

capability for applicants to effectively 

demonstrate compliance with this final 

rule. The IPHWG evaluated the current 

capabilities of these tools in 2008–2009 

during a review requested by industry 

members through ARAC. The IPHWG 

evaluation of SLD engineering tools, 

which proposed methods of compliance 

based on the current state of the 

available engineering tools, supports the 

FAA conclusion. The FAA considered 

estimates provided by industry and has 

made adjustments to the proposed 

economic evaluation, which is 

incorporated in the economic evaluation 

for this final rule. This adjustment 

increases the cost for complying with 

the requirements of this final rule; 

however, this final rule remains cost 

beneficial. A summary of the final 

regulatory evaluation is provided in the 

‘‘Regulatory Notices and Analyses’’ 

section of this final rule and the 

complete document is included in the 

public docket. 

As to freezing drizzle, the current 

icing wind tunnel test capabilities for 

SLD icing conditions have been 

demonstrated. However, we recognize 

that some limitations exist: Icing wind 

tunnel spray systems evaluated during 

the IPHWG’s review do not support bimodal mass distributions (mass ‘‘peaks’’ 

for two different drop sizes) provided in 

appendix O and do not produce realistic 

freezing rain simulations for the 


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7A copy of this report is available in the rule 

Docket No. FAA–2010–0636. 

majority of those conditions. NASA 

examined alternate spray methods to 

simulate portions of a bi-modal spray 

using spray sequencing techniques to 

approximate drop distributions found in 

natural conditions (reference: American 

Institute of Aeronautics and 

Astronautics report AIAA 2005–76, 

Simulation of a Bimodal Large Droplet 

Icing Cloud in the NASA Icing Research 

Tunnel 7). NASA demonstrated the 

water spray sequencing technique for an 

airfoil with unprotected surfaces and 

the results showed rougher ice accretion 

textures than appendix C ice shapes. 

Experience indicates that SLD icing 

conditions generally result in rougher 

ice accretion textures. NASA has also 

developed preliminary scaling methods 

for SLD test applications and has 

developed large droplet algorithm 

improvements to its ice accretion 

prediction code by adding SLD 

subroutines. Other ice accretion code 

developers have incorporated SLD 

capabilities in their respective 

computational tools. A number of icing 

wind tunnel owners have tested SLD 

icing conditions in their facilities and 

are capable of performing tests for at 

least a portion of the appendix O 

environments. 

Regarding flight testing, § 25.1420 

requires that applicants provide analysis 

to establish that ice protection for the 

various airplane components is 

adequate, taking into account the 

various operational configurations. 

Section 25.1420 also describes flight 

testing in natural or simulated icing 

conditions, as necessary, to support the 

analysis. The IPHWG acknowledged the 

difficulties in flight testing in natural 

SLD, and agreed it would not be 

specifically required under § 25.1420. 

We concur, and have left flight testing 

as an option in the regulation. Until the 

engineering tools become more mature, 

flight tests in natural appendix O icing 

conditions may be necessary to achieve 

certification for unrestricted flight in 

appendix O conditions in accordance 

with § 25.1420(a)(3). 

Proposed Revisions to § 33.68 Should 

Not Apply to Engines Installed on 

Rotorcraft 

Eurocopter and Turbomeca noted the 

proposed part 33 changes would apply 

to all turbine engines, including 

turboshaft engines intended for 

installation in rotorcraft. The proposed 

revision to § 33.68 would require all 

turbine engines to be capable of 

operating in the extended icing 

conditions defined in part 25, appendix 

O. However, the IPHWG task 2 report 

and the NPRM only addressed airplane 

accidents and incidents; it did not 

include rotorcraft. Eurocopter and 

Turbomeca proposed provisions to 

exclude rotorcraft from the new engine 

requirements. The FAA did not receive 

any comments providing specific 

support for the proposed applicability to 

rotorcraft. 

We agree. The IPHWG did not review 

rotorcraft accidents or incidents in icing 

conditions and did not propose 

rulemaking associated with rotorcraft. 

As a result, we revised the proposed 

§ 33.68 to separate the icing 

requirements for turboshaft engines 

used for rotorcraft from turbojet, 

turbofan, and turboprop engines used 

for airplanes. The icing requirements 

pertaining to turboshaft engines are 

unchanged and require that turboshaft 

engines operate safely throughout the 

icing conditions defined in part 29, 

appendix C. Section 33.68 now requires 

that turbojet, turbofan, and turboprop 

engines not installed on rotorcraft 

operate safely throughout the icing 

conditions defined in part 25, appendix 

C, the SLD conditions defined in part 

25, appendix O, and the mixed phase 

and ice crystal conditions defined in 

part 33, appendix D. 

Applicability of Proposed § 25.1420 

In the NPRM, the FAA proposed to 

add a new § 25.1420. Proposed 

§ 25.1420 would have required specific 

airplanes certified for flight in icing 

conditions to be capable of either: (1) 

Operating safely within the new SLD 

icing conditions defined in part 25, 

appendix O; (2) operating safely in a 

portion of the new appendix O 

conditions, with the capability to detect 

when conditions beyond those used for 

certification have been encountered, 

and then safely exit all icing conditions; 

or (3) have a means to detect when 

appendix O icing conditions are 

encountered, and be capable of safely 

exiting all icing conditions. The FAA 

proposed to limit the applicability of 

§ 25.1420 to airplanes that have a 

maximum takeoff weight (MTOW) of 

less than 60,000 pounds, or airplanes 

equipped with reversible flight controls 

regardless of MTOW. 

The applicability of § 25.1420 was 

discussed within the IPHWG and 

consensus could not be reached. A 

discussion of this issue was provided in 

the NPRM under the heading 

‘‘Differences from the ARAC 

Recommendations.’’ Bombardier, ALPA, 

EASA, Goodrich, Gulfstream, the NTSB, 

and the TCCA provided comments to 

the NPRM that supported the majority 

position of the IPHWG, questioning the 

technical justification used to exclude 

airplanes with a MTOW of 60,000 

pounds or greater. Airbus, AIA, Boeing, 

and GAMA provided comments in 

response to the NPRM to support the 

proposed applicability based on MTOW 

because airplanes with a MTOW of 

60,000 pounds or greater have not 

previously experienced accidents or 

incidents associated with flight in SLD. 

Embraer and Pratt & Whitney Canada 

comments to the NPRM specifically 

noted support for AIA’s position. 

A review of the IPHWG analysis 

indicates that airplanes with a MTOW 

of 60,000 pounds or greater have not 

experienced accidents or incidents 

associated with flight in SLD. The FAA 

originally considered including all new 

airplanes in the applicability for 

§ 25.1420, regardless of MTOW; 

however, the projected costs of 

extending the rule to include airplanes 

with a MTOW of 60,000 pounds or 

greater exceeded the projected benefits 

due to the positive in-service history 

(i.e., lack of accidents) of these airplanes 

in SLD. 

The commenters did not present any 

new data or information that was not 

discussed within the IPHWG, or 

discussed within the NPRM. The 

commenters that opposed limiting the 

applicability of the rule suggested that 

lift and control surface size, or wing 

chord length, are important parameters 

affecting sensitivity to a given ice 

accretion. They based their opposition 

on airplane weight, in part, because the 

ratio of wing and control surface sizes 

to airplane weight varies between 

airplane designs. 

We agree that design features such as 

control surface size and wing chord 

length are important parameters, which 

can affect the sensitivity of a wing to the 

icing conditions described in part 25, 

appendix O. As proposed in the NPRM, 

in order to issue a rule with estimated 

costs commensurate with the estimated 

benefits, the applicability of § 25.1420 is 

limited based on airplane weight due to 

the positive service histories of certified 

airplanes. 

If future designs for larger airplanes 

contain novel or unusual design features 

that affect this successful in-service 

history, and those design features make 

the airplane more susceptible to the 

effects of flight in SLD icing conditions, 

the FAA can issue special conditions to 

provide adequate safety standards. The 

FAA issues special conditions in 

accordance with § 21.16. No changes 

have been made to the applicability of 

§ 25.1420 as a result of these comments. 


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65514 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 

8NTSB Safety Recommendation A–07–16 is 

available in the rule Docket No. FAA–2010–0636 

and on the Internet at http://www.ntsb.gov/doclib/ 

recletters/2007/A07_12_17.pdf. 

9AD 2006–21–02, Docket No. FAA–2006–26004, 

published in the Federal Register on October 10, 

2006 (71 FR 29363), is applicable to Raytheon 

(Beech) Model 400, 400A, and 400T series 

airplanes; and Raytheon (Mitsubishi) Model MU– 

300 airplanes. 

Clarification of Definitions 

Embraer noted that § 25.1420(b) uses 

the terms ‘‘simulated icing tests’’ and 

‘‘simulated ice shapes’’ in various 

subparagraphs. Embraer suggested that 

subparagraphs § 25.1420(b)(1) and (b)(2) 

use the phrase ‘‘artificial ice’’ as defined 

in Advisory Circular (AC) 25–28, 

Compliance of Transport Category 

Airplanes with Certification 

Requirements for Flight in Icing 

Conditions, instead of ‘‘simulated icing 

tests.’’ 

We do not agree. Section 

25.1420(b)(1) and (b)(2) describe test 

methods, not the resulting ice shapes. 

The terminology ‘‘simulated icing tests’’ 

is used in § 25.1420 consistently with 

§ 25.1419. We added definitions for 

‘‘Simulated Ice Shape’’ and ‘‘Simulated 

Icing Test’’ to § 25.1420 that are 

consistent with previously issued 

guidance. 

AIA, Boeing, and GAMA suggested a 

clarification to the definition of 

‘‘reversible flight controls.’’ AIA and 

GAMA suggested that the addition of 

servo tab inputs in the examples 

provides a more complete and accurate 

description. 

We agree and have clarified the 

definition of ‘‘reversible flight controls’’ 

to include the example of servo tab 

inputs. In addition, since the definition 

of ‘‘reversible flight controls’’ is 

necessary to determine the applicability 

of § 25.1420, we added the definition to 

§ 25.1420. 

Applicability of Proposed Appendix O 

Icing Conditions to Part 23 Airplanes 

and Previously Certified Part 25 

Airplanes 

The NTSB and a private citizen 

commented that the icing conditions 

proposed in appendix O should be 

applicable to part 23 airplanes because 

they are the type of airplanes most 

affected by flight into icing conditions. 

The NTSB also stated that the proposed 

rule should be expanded beyond newly 

certified airplanes to include all deice 

boot-equipped airplanes currently in 

service that are certified for flight in 

icing conditions (reference NTSB Safety 

Recommendation A–07–16).8 The NTSB 

pointed out SLD is an atmospheric 

condition that can create dangerous 

flight conditions for both the current 

fleet of aircraft and newly certified 

aircraft. 

Regarding the applicability of 

proposed appendix O to part 23 

airplanes, we disagree with adding part 

23 airplanes to the applicability, as that 

is beyond the scope of this rulemaking. 

However, we chartered an Aviation 

Rulemaking Committee (ARC) to review 

the IPHWG’s rulemaking 

recommendations for part 25 and to 

make similar recommendations for part 

23. The ARC transmitted a report 

detailing part 23 rulemaking 

recommendations to the FAA in a letter 

dated February 19, 2011, and provided 

supplemental recommendations in a 

letter dated April 27, 2011. The ARC 

transmitted its recommendations for a 

final task in early 2012. We are studying 

these recommendations and may pursue 

additional rulemaking for part 23 

airplanes. 

We agree that severe icing conditions, 

including SLD, can create dangerous 

flight conditions for both current and 

future airplanes. However, we do not 

agree that the part 25 and part 33 rule 

changes discussed in this amendment 

should apply to existing airplanes. Such 

a retroactive application would, in 

effect, be changing the certification basis 

of operational airplanes to correct an 

unsafe condition, something generally 

done by airworthiness directive (AD). 

To address the unsafe condition, we 

have already issued ADs to mandate 

procedures to activate the ice protection 

equipment at the first sign of ice 

accretion, and to incorporate procedures 

into the AFM so the flightcrew can 

identify when they are in severe icing 

conditions that exceed certificated 

limitations, and safely exit. 

New airworthiness standards are not 

intended to correct an unsafe condition; 

rather, they are intended to improve the 

level of safety for new airplane designs. 

In the context of SLD, we are 

considering operational rules to 

mandate certain elements of the 

airworthiness standards adopted in this 

rulemaking for previously certified 

airplanes. However, those requirements 

are beyond the scope of this rulemaking 

and require separate rulemaking action. 

Applicability of Part 33, Appendix D, to 

§ 25.1093, Induction System Icing 

Protection, and § 33.68, Induction 

System Icing 

The NTSB supported changes to 

§§ 33.68 and 33.77, noting that since we 

issued an icing-related AD for the 

Beechjet 400A no additional reports of 

unsafe icing conditions on that airplane 

have been noted. The FAA infers that 

the NTSB was referring to AD 2006–21– 

02.9 That AD was issued following 

reports of dual engine flameouts in high 

altitude icing conditions believed to 

include ice crystals. AIA, Airbus, 

Boeing, and GAMA supported the 

addition of mixed phase and ice crystal 

conditions, such as those defined in part 

33, appendix D. 

Honeywell commented that the 

current lack of and/or immature state of 

engine test facilities to demonstrate 

compliance to part 33, appendix D, 

could result in a significant increase in 

an applicant’s activities to show 

compliance because of the additional 

flight testing required to locate the ice 

crystal conditions. Honeywell also 

noted that flying in actual ice crystal 

conditions would put the flightcrew at 

considerable risk. Honeywell 

recommended that appendix D be 

removed until test facilities have 

developed the capabilities to run tests 

for ice crystal conditions. Honeywell 

also suggested that the FAA make 

research funds available to facilities to 

develop this capability. 

We agree, in part. We agree that only 

limited capability exists for testing 

engines in ice crystal conditions. We 

also agree that flightcrews unnecessarily 

operating in icing conditions puts them 

at risk. We do not agree, however, that 

appendix D should be removed until 

test facilities develop the capabilities to 

run tests for ice crystal conditions, or 

that FAA make funds available for 

research to develop these capabilities. 

Section 33.68(e) allows for certification 

demonstration by test, analysis, or 

combination of the two. Consistent with 

ARAC Engine Harmonization Working 

Group (EHWG) recommendations, until 

ice crystal tools and test techniques 

have been developed and validated, the 

engine manufacturer may use a 

comparative analysis to specific field 

events. This analysis should show that 

the new engine cycle or design feature, 

or both, would result in acceptable 

engine operation when operating in the 

ice crystal environment defined in 

appendix D to part 33. This comparative 

analysis should also take into account 

both suspected susceptible design 

features, as well as mitigating design 

features. We did not change the rule 

based on this comment. 

GSIS suggested that provisions be 

made for a detect-and-exit strategy for 

part 33, appendix D, conditions; similar 

to what was proposed in the NPRM for 

part 25, appendix O, conditions. 

We disagree. We do not believe part 

33, appendix D, conditions can be 

detected with enough time to exit before 

damage occurs. Therefore, a detect-andVerDate Sep<11>2014 18:18 Nov 03, 2014 Jkt 235001 PO 00000 Frm 00008 Fmt 4701 Sfmt 4700 E:\FR\FM\04NOR2.SGM 04NOR2

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Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 65515 

exit strategy for part 33, appendix D, 

conditions is inappropriate. As 

proposed in the NPRM, the mixed phase 

and ice crystal icing conditions defined 

in part 33, appendix D, have been added 

to §§ 25.1093(b)(1) and 33.68(a). 

Applicability of Proposed Appendix O 

to § 25.1093, Induction System Icing 

Protection, and § 33.68, Induction 

System Icing 

AIA, Airbus, Boeing, and GAMA 

provided comments that there are no 

known events that support a safety 

concern due to engine induction system 

icing in SLD aloft. In particular, the 

EHWG evaluated known icing-related 

engine events since 1988 and found no 

events in SLD aloft. The EHWG credited 

this result to the current rigorous 

compliance to part 25, appendix C, 

conditions for engines. The commenters 

believe that the safety of these systems 

for flight in appendix O conditions has 

already been proven by service history. 

The commenters state that continuing to 

certify future systems to the 

requirements for appendix C icing 

conditions, in conjunction with 

consideration of excellent service 

history of similar designs in appendix O 

conditions, should be acceptable 

assurance of the safety of future designs. 

The commenters suggested that 

consideration of the icing conditions 

defined in appendix O be removed from 

§ 25.1093. 

We agree that there are no known 

events that support a safety concern due 

to engine induction system icing in SLD 

aloft. However, there have been reports 

of engine fan damage or high vibration 

while operating in SLD icing conditions. 

The ARAC database on engine events 

contains 231 icing events reported by 

engine manufacturers from 

approximately 1988 through 2003, and 

includes part 25, appendix C; part 25, 

appendix O; and part 33, appendix D 

events. Although the intent of the event 

database was to focus on icing events 

outside of appendix C, there are several 

appendix C events included in this 

database. The event database does not 

include any accidents. 

The EHWG identified 46 part 25, 

appendix O (SLD) events. All events 

occurred on the ground and resulted in 

fan damage and/or high vibrations so a 

precise effect on the safety of these 

events was not discernible. 

Additionally, the EHWG identified 

nine additional events that it thought 

might have been related to operations in 

SLD icing conditions: Four were inflight and all nine were on tail mounted 

engine configurations. Again, the events 

resulted in fan damage and/or high 

vibrations, with indeterminable power 

loss. Although these nine events are of 

concern, the EHWG did not judge them 

to be safety significant. 

An additional 14 in-flight events were 

not clearly identifiable as SLD events 

but were described as heavy icing below 

22,000 feet and resulted in fan damage 

and/or high vibrations. These events did 

not clearly fall within conditions 

defined in either appendix C or 

appendix O. However, the general 

description of the icing conditions and 

engine damage is consistent with 

reports of engine damage that occurred 

within the icing conditions defined in 

appendix O, so those might have been 

SLD events. 

After reviewing the data, the EHWG 

clearly identified SLD as a threat for 

engine damage during ground 

operations. Furthermore, the EHWG 

could not rule out SLD as a potential inflight safety threat, and decided to 

include it as part of its 

recommendations to the FAA. As 

proposed in the NPRM, the part 25, 

appendix O, SLD icing conditions have 

been added to § 33.68. Also, as proposed 

in the NPRM, § 33.77 contains 

requirements to demonstrate engine 

capability to ingest the applicable 

minimum ice slab defined in Table 1 of 

§ 33.77. The ice slab sizes defined in 

Table 1 of § 33.77 are a function of the 

engine inlet diameter. Turbojet, 

turbofan, and turboprop engine 

manufacturers must demonstrate, in 

part, that the engine will continue to 

operate throughout its power range in 

the icing conditions defined in part 25, 

appendix O, and following ingestion of 

an ice slab that is a function of the 

engine inlet diameter. The changes to 

the requirements in §§ 33.68 and 33.77 

are intended to improve the level of 

safety for turbojet, turbofan, and 

turboprop engines used on transport 

category airplanes in icing conditions, 

in part because of reports of engine 

damage or high engine vibrations while 

operating in SLD conditions. 

We agree large airplanes that have 

likely encountered appendix O 

conditions have had a successful inservice history with no clearly 

identifiable safety significant events. 

After considering the comments 

received, we revised § 25.1093(b), 

compared to what was proposed in the 

NPRM, so consideration of the icing 

conditions described in appendix O 

does not apply to airplanes with a 

MTOW equal to or greater than 60,000 

pounds. As proposed in the NPRM, the 

applicability of the icing conditions 

described in part 25, appendix C; part 

33, appendix D; and falling and blowing 

snow remain applicable to all turbine 

engine installations on transport 

category airplanes. In addition, the 

engine requirements in §§ 33.68 and 

33.77 for operation in all icing 

conditions still apply to engines 

installed on part 25 airplanes regardless 

of the airplanes’ MTOW. The 

applicability of appendix O conditions 

in § 25.1093(b) as a function of airplane 

weight is consistent with the revised 

applicability of § 25.1420, which 

establishes minimum airworthiness 

standards for detection and safe 

operation in appendix O conditions. 

Airplanes that have been susceptible to 

performance issues while operating in 

SLD icing conditions have been smaller 

airplanes with a MTOW less than 

60,000 pounds. 

Section 25.1093(b) was revised to 

provide relief for larger airplanes 

because of the successful in-service 

history of existing larger airplane 

designs and larger airplane engine inlet 

designs. As previously discussed, the 

changes to the requirements in §§ 33.68 

and 33.77 are intended to improve the 

level of safety for turbine engines used 

on all airplanes, including large 

airplanes, while operating in SLD 

conditions. If future designs for larger 

airplanes contain novel or unusual 

design features that affect this 

successful in-service history, and those 

design features make the airplane more 

susceptible to the effects of flight in SLD 

icing conditions, the FAA can issue 

special conditions to provide adequate 

safety standards. 

Boeing, AIA, and GAMA also 

provided comments on the results of an 

SLD analysis, including the use of the 

NASA Lewis Ice Accretion Program, 

commonly referred to as LEWICE. The 

analysis yielded overly conservative 

accreted ice mass calculations resulting 

in large amounts of ice on the radome. 

The results from this analysis indicated 

to Boeing that radome ice shedding 

would be a concern, and it would 

require ice protection on the currently 

unprotected radome surfaces to reduce 

ice build-up to acceptable limits. The 

weight increase for radome ice 

protection equipment would result in 

increased fuel burn and increased 

operational costs that were not included 

in the IPHWG economic analysis. 

Boeing also stated that most large 

airplanes are operating without 

restrictions today and are safely 

encountering SLD conditions. 

Analytical methods used by Boeing to 

determine SLD ice accretions on 

radomes show considerably higher ice 

mass accretions than either past 

calculations or past experience has 

indicated for other icing conditions. 

These analyses were never presented to 

the IPHWG and details were not 


tkelley on DSK3SPTVN1PROD with RULES2
65516 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 

10NTSB Investigation No. DFCA01MA031, 

Embraer EMB–120 Zero Injury Incident Near West 

Palm Beach, Florida on March 19, 2001, http:// 

www.ntsb.gov. 

11FAA Data Report DOT/FAA/AR–06/60, 

Propeller Icing Tunnel Test on a Full-Scale 

Turboprop Engine, dated March 2010. A copy of 

this report is available in the rule Docket No. FAA– 

2010–0636. 

included with Boeing’s comments to 

support the FAA’s evaluation of 

Boeing’s methods. As previously 

discussed, we revised § 25.1093(b) 

compared to what was proposed in the 

NPRM. For the purposes of compliance 

with § 25.1093(b), the icing conditions 

defined in appendix O are not 

applicable to airplanes with a MTOW 

equal to or greater than 60,000 pounds. 

To show compliance with § 25.1093(b), 

analysis may be used for the radome as 

a potential airframe ice source. For 

compliance with § 25.1093(b), 

applicants may use qualitative analysis 

supported by similarity to a previous 

design with a successful service history 

to show that ice accretions ingested into 

the engine from the new airplane design 

will be less than the ice slab size 

presented in § 33.77 Table 1, ‘‘Minimum 

Ice Slab Dimensions Based on Engine 

Inlet Size.’’ 

Applicability of Proposed Appendix O 

to § 25.773, Pilot Compartment View 

AIA, Airbus, Boeing, and GAMA 

commented that there are no known 

events that support a safety concern due 

to windshield icing in SLD aloft. The 

commenters state the safety of these 

systems for flight in appendix O 

conditions has been proven by service 

history. They believe that continuing to 

certify future systems to the 

requirements for appendix C icing 

conditions, in conjunction with 

consideration of excellent service 

history of similar designs in appendix O 

conditions, should be an acceptable 

assurance of the safety of future designs. 

One commenter, an individual, 

commented that § 25.773 should not be 

changed, as ice accretion on the 

windshield is one of the few indications 

used to recognize the condition. 

We do not agree. Section 25.773 is 

intended to ensure that a clear portion 

of the windshield is maintained in icing 

conditions, which enhances safety in 

icing conditions. For airplanes certified 

to detect appendix O conditions, or a 

portion of appendix O conditions, and 

required to exit all icing conditions 

when the icing conditions used for 

certification have been exceeded, the 

pilot must have a clear view out the 

windshield; not only when the airplane 

is in appendix O icing conditions, but 

also during the time it takes to detect 

and exit all icing conditions within 

which the airplane is not approved to 

operate. For airplanes not certified with 

the detect-and-exit strategy, appendix C 

and appendix O conditions need to be 

considered for the entire time the 

airplane is in the applicable icing 

conditions. 

Section 25.773 does not require the 

windshield to be completely free of ice 

in all icing conditions. Therefore, this 

requirement does not preclude using ice 

accreting in certain locations on the 

windshield as an indication that the 

airplane is in icing conditions beyond 

those in which it is approved to operate. 

We did not change the rule based on 

these comments. 

Applicability of Proposed Appendix O 

to § 25.1323, Airspeed Indicating 

System, § 25.1324, Angle of Attack 

System, and § 25.1325, Static Pressure 

Systems 

AIA, Airbus, Boeing, and GAMA 

commented that there are no known 

events that support an in-flight safety 

concern for angle of attack systems in 

SLD aloft. They believe the safety of 

these component systems for flight in 

appendix O conditions has already been 

proven by service history. The 

commenters recommended the reference 

to appendix O be removed from the 

requirements in §§ 25.1323, 25.1324, 

and 25.1325. 

We do not agree. If certification for 

flight in icing is desired, part 25 

requires the airplane to be capable of 

safely operating in icing conditions. The 

airplane and its components are taken 

into account during flight in icing 

certification programs. For these 

reasons, all icing conditions should be 

considered. Sections 25.1323, 25.1324, 

and 25.1325 include considerations for 

the SLD icing environment defined in 

part 25, appendix O. 

Applicability of Proposed Appendix O 

to § 25.929, Propeller Deicing 

AIA and GAMA commented that 

there are no known events that support 

a safety concern with propeller icing in 

SLD. In particular, AIA and GAMA 

noted the EHWG evaluated all known 

icing-related events since 1988 and 

found no events in SLD aloft. The 

commenters credit the current rigorous 

compliance using appendix C 

conditions for this result. The 

commenters believe the safety of these 

systems for flight in appendix O 

conditions has already been proven by 

service history. They further believe that 

continuing to certify future systems to 

the requirements for appendix C icing 

conditions, in conjunction with 

consideration of excellent service 

history of similar designs in appendix O 

conditions, should be acceptable 

assurance for the safety of future 

designs. 

We do not agree. Propeller icing is 

typically not implicated in events 

because ice accretion on the propeller is 

usually not visible in flight. However, in 

one suspected SLD event 10 included in 

the IPHWG list of applicable events, the 

NTSB Performance Group reported that 

the flight data recorder derived drag 

increment was much higher than an 

increment measured in flight test with 

intercycle ice (by a factor of 2 near the 

time where the pilot lost control of the 

airplane). The NTSB report does not 

speculate what caused the large drag 

increment, but it could have been 

airframe SLD ice accretion, propeller 

SLD ice accretion, or a combination of 

both. In addition, appendix J in AC 20– 

73A, Aircraft Ice Protection, dated 

August 16, 2006, documents a flight test 

encounter in which suspected SLD 

caused a severe performance penalty 

due to propeller ice accretion. FAA 

research tests, documented in report 

DOT/FAA/AR–06/60, Propeller Icing 

Tunnel Test on a Full-Scale Turboprop 

Engine,11 have duplicated the event 

discussed in the AC, and showed that 

propeller ice accretion and resulting 

propeller efficiency loss is greater in 

SLD compared to appendix C 

conditions. 

After further consideration, we have 

revised § 25.929 to require a means to 

prevent or remove hazardous ice 

accumulations that could form in the 

icing conditions defined in appendix C 

and the portions of appendix O for 

which the airplane is approved for 

flight. As compared to the NPRM, the 

phrase ‘‘defined in appendices C and O’’ 

has been replaced with ‘‘defined in 

appendix C and in the portions of 

appendix O of this part for which the 

airplane is approved for flight.’’ 

A private citizen commented that the 

words ‘‘would jeopardize engine 

performance’’ in the last portion of 

§ 25.929(a) makes this requirement 

specific to engine performance. The 

commenter requested that the words be 

stricken from the regulation. The 

commenter did not provide justification 

to substantiate his proposed change. 

We do not agree. First, we did not 

propose a change to this portion of the 

rule. Second, we reviewed the wording 

presented by the IPHWG and agree with 

its intent and its phrasing. Its 

applicability is broader than just an 

engine rule. We did not change the rule 

based on this comment. 


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Engine and Engine Installation 

Requirements 

The RAA commented that current 

facilities lack the capability to test large 

turbofans at very cold temperatures, 

and, while new sites may come on-line 

in the future, such facilities could not be 

constructed to comply with the 

proposed test conditions. The RAA also 

pointed out that future airplanes would 

not be certified for operations below 

zero degrees Fahrenheit when ‘‘freezing 

fog’’ is present, so it would create a 

restriction to what is currently 

considered a safe operating condition. 

Airbus, AIA, Boeing, GAMA, GE, and 

a private citizen suggested that the 

choice of ambient temperature for the 

ground freezing fog rime icing 

demonstration should be driven by 

critical point analysis, as required by 

§ 33.68(b)(1). This analysis could also be 

used to show that a more critical point 

does not exist at temperatures below the 

Table 1, condition 2, test temperatures 

in § 33.68. Airbus, AIA, Boeing, GAMA, 

GE, a private citizen, and RAA further 

suggested that the applicant should be 

permitted to use analysis to demonstrate 

safe operation of the engine at 

temperatures below the required test 

demonstration temperature. If safe 

operation is shown by this analysis, a 

temperature limitation would not be 

required for the AFM. 

Airbus also suggested a further change 

to § 25.1093(b)(2) to ensure that the test 

is performed in accordance with aircraft 

procedures to provide adequate 

conservatism. These procedures are 

defined in collaboration with the engine 

manufacturer and may be defined on the 

basis of engine certification or 

development test results. 

EASA and the FAA have recently 

addressed cold ground fog conditions. 

Specifically, the choice of ambient 

temperature for the ground freezing fog 

rime icing demonstration should be 

driven by critical point analysis (as 

required by § 33.68(b)(1)). We 

determined this analysis may also be 

used to show that at colder temperatures 

below the Table 1, condition 2, test 

temperatures in § 33.68, a more critical 

point does not exist. The analysis may 

also be used to demonstrate safe 

operation of the engine at temperatures 

below the required test demonstration. 

If an applicant does not show unlimited 

cold temperature operation, then the 

minimum ambient temperature that was 

demonstrated through test and analysis 

should also be a limitation. Finally, the 

acceleration to takeoff power or thrust 

should be accomplished in accordance 

with the procedures defined in the 

AFM. As a result, we changed 

§§ 25.1093(b)(2) and 25.1521(c)(3) based 

on these comments, to reflect these 

changes and recent developments with 

EASA. 

AIA, GAMA, and a private citizen 

commented that the MVD for high LWC 

in Table 2 of § 33.68 may be difficult to 

achieve in practice due to icing facility 

constraints, and may result in repetitive 

equivalent level of safety (ELOS) 

findings. Expanding the upper limits of 

droplet size ranges will allow flexibility 

in test demonstrations. An upper limit 

of 30 microns for glaze ice conditions 

(points 1 and 3 in Table 1) and 23 

microns for rime ice conditions (point 2 

in Table 1) can be accepted if the critical 

point analysis shows that the engine is 

tested to equivalent or greater severity. 

AIA, GAMA, and a private citizen 

also suggested changes to the drop 

diameters in Table 1 of § 33.68, noting 

that practical application of the required 

conditions dictates a wider acceptable 

droplet diameter range, without 

measurably impacting the severity of the 

intended engine test demonstration. 

We agree. Although the commenters 

did not provide any data to validate the 

suggested change in drop diameters, we 

are aware of test facility limitations, and 

concur that the upper tolerance of drop 

size is limiting for some test facilities. 

As a result, the proposed ±3 micron 

droplet tolerance has been removed and 

a range for the MVDs is specified 

instead. This will still provide an 

adequate safety margin. Likewise, the 

upper drop size limit has also been 

increased to represent current test 

facility capabilities while preserving an 

adequate safety margin. Section 33.68, 

Table 1, has been revised to reflect these 

changes. 

AIA and GAMA also suggested that 

the ground test conditions in Table 1, 

condition (iii), of § 25.1093 and Table 2, 

condition 4, of § 33.68(d) should have a 

consistent range of droplet sizes based 

on the values from part 25, appendix O. 

We agree. We changed Table 2, 

condition 4, in § 33.68 by removing the 

maximum drop diameter so it is 

consistent with Table 1, condition (iii), 

in § 25.1093. Table 2 in § 33.68 was also 

revised to correct the conversion of 

degrees Centigrade to degrees 

Fahrenheit. 

A private citizen remarked that 

including parenthetical examples in the 

rule text of § 33.68(a)(3) was not helpful 

and may be construed to be 

exclusionary of other pertinent, topical 

considerations. Furthermore, their 

absence does not diminish the clarity or 

understanding of the requirement. 

We agree. We removed the 

parenthetical examples from the 

regulatory text in § 33.68. 

A private citizen suggested a word 

change to our proposed wording of 

§ 33.68(d). In the NPRM, we proposed to 

change § 33.68(d) to state that the engine 

should be run at ground idle speed for 

a minimum of 30 minutes in each of the 

icing conditions shown in Table 2. The 

commenter suggested replacing the 

phrase ‘‘should be run’’ with ‘‘must 

demonstrate the ability to acceptably 

operate.’’ The commenter noted that use 

of the word ‘‘should’’ is ambiguous and 

contrary to existing § 33.68, which uses 

the word ‘‘must.’’ Furthermore, the 

commenter suggested that eliminating 

the word ‘‘run’’ would be more 

consistent with the demonstration 

methods for snow, ice, and large drop 

glaze ice conditions (i.e., test, analysis, 

or combination of both) shown in Table 

2 of § 33.68. 

We agree and have clarified 

§§ 25.1093(b)(2) and 33.68(d) to state 

that the engine must operate at ground 

idle speed in the specified icing 

conditions. 

Alternatives to Rulemaking 

Several commenters said that 

operational solutions have proven to be 

extremely effective in managing weather 

related risks (e.g., thunderstorms and 

windshear). They suggested that the 

FAA should have been, or should start, 

placing at least as much emphasis on 

advancing alternatives to rulemaking as 

it does on creating new certification 

requirements. ALPA encouraged 

continuous research and development 

of technical systems that would 

automatically detect the presence of 

hazardous ice, measure the rate of 

accumulation, and then alert the crew as 

appropriate to take action in order to 

avoid a potentially unsafe flight 

condition. AirDat, LLC, commented that 

the FAA may have overlooked state-ofthe-art meteorological tools, including 

airborne sensors, that are commercially 

available today, fully deployed, and in 

operation. AIA, Airbus, Boeing, and 

GAMA commented that the IPHWG did 

not thoroughly consider any alternatives 

to new rulemaking because the tasking 

statement did not include this option. 

We agree in part. We agree that 

careful operations and new technologies 

may often enhance safety. However, we 

note that rulemaking is at the discretion 

of the agency, and we have exercised 

our discretionary rulemaking authority 

in this instance. This rule provides 

additional safety for the flying public 

when icing conditions are encountered, 

and it will improve the level of safety 

of future airplane designs. 


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65518 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 

12This report can be found on the BEA Web site 

at http://www.bea.aero/docspa/2009/fcp090601e2.en/pdf/f-cp090601e2.en.pdf. 

Applicability of Mixed Phase and Ice 

Crystal Conditions to Airspeed 

Indicating Systems 

We received several comments 

suggesting that the mixed phase and ice 

crystal environment in part 33, 

appendix D, should be used instead of 

the mixed phase and ice crystal 

environment that was proposed in Table 

1 of § 25.1323. AIA, Airbus, Boeing, and 

GAMA stated the NPRM acknowledged 

new information is available to guide 

development of an ice crystal envelope 

appropriate for evaluation of airspeed 

indication systems. They also noted that 

proposed Table 1 of § 25.1323 does not 

reflect the current understanding of the 

ice crystal environment, nor does it 

include known pitot icing events, which 

are published in ‘‘Interim Report no. 2,’’ 

Bureau D’Enquetes et D’Analyses pour 

la securite d’aviation civile (BEA) F– 

GZCP.12 GSIS recommended that Table 

1 of § 25.1323, which defines a subset of 

part 33, appendix D, conditions, should 

be removed. Instead, the rule should 

require that airspeed indication systems 

must not malfunction in any of the 

conditions specified in appendix D. 

EASA stated that the proposed 

environment in Table 1 of § 25.1323 

would not address known events of 

airspeed indicating system 

malfunctions. EASA also fully 

supported including in part 25, the 

proposed mixed phase and ice crystal 

parameters in proposed part 33, 

appendix D. TCCA suggested that the 

FAA reconsider the icing conditions for 

the airspeed indicating system proposed 

in the NPRM within Table 1 of 

§ 25.1323 and include the ¥60 °C 

conditions described in part 33, 

appendix D, instead. 

Airbus supported the application of 

appendix D icing conditions to pitot and 

pitot-static probes, but pointed out it is 

necessary to develop an acceptable 

means of compliance that takes into 

account the capabilities of the existing 

engineering tools (for example, models 

and icing tunnels) and provide guidance 

on these new requirements. GSIS also 

commented that recent testing suggests 

testing at sea level atmospheric 

conditions may not be a conservative 

assumption for ice crystal testing. 

NRC noted the requirements of 

§ 25.1323 do not appear to take into 

account the effects of displacing the free 

stream ice water content around the 

fuselage of the airplane. If the probe is 

in a region affected by this, then the 

concentration detected by the probe 

would be higher than that of the free 

stream. Airbus mentioned that one test 

facility has made significant 

improvements in its capability to 

reproduce icing conditions but it is 

limited by the size of the test article it 

can accommodate. However, no test 

facilities are currently capable of 

reproducing the full range of icing 

conditions and flight conditions 

required by part 33, appendix D. 

Considering the state of the art of the 

engineering tools, there is a need for an 

agreed means of compliance. 

We agree that the mixed phase and ice 

crystal environment in part 33, 

appendix D, should be used instead of 

the mixed phase and ice crystal 

environment proposed in Table 1 of 

§ 25.1323. Therefore, §§ 25.1323 and 

25.1324 have been revised to add a 

requirement to prevent malfunctions in 

the mixed phase and ice crystal 

environment defined in part 33, 

appendix D. 

With regard to comments suggesting 

that testing at sea level atmospheric 

conditions may not be a conservative 

assumption, or that ice crystal 

concentrations at an exterior mounted 

probe could be higher than the free 

stream conditions, we agree. The 

conditions defined in part 33, appendix 

D, are atmospheric conditions. These 

atmospheric conditions include 

parameters for total water content as a 

function of temperature, altitude, and 

horizontal extent. We also agree that 

altitude may be an important parameter. 

Altitude is a parameter identified in part 

33, appendix D, and must be considered 

when developing the test conditions 

and supporting analysis necessary to 

show compliance. 

We also agree that depending on 

airplane size and the location of the 

probe, the ice water content at the probe 

may be higher than the ice water 

content values defined in part 33, 

appendix D. Since part 33, appendix D, 

describes atmospheric conditions, the 

potential for higher ice crystal 

concentrations at the probe location 

compared to the atmospheric 

concentrations defined in part 33, 

appendix D, must be considered when 

developing the test conditions and 

supporting analysis necessary to show 

compliance. Installation effects could be 

evaluated with a combination of 

computational fluid dynamics codes 

and icing tunnels. Devices mounted on 

smaller surfaces could be assessed in an 

icing tunnel. However, if the device is 

mounted on the fuselage and tunnel 

blockage effects would preclude a 

meaningful icing tunnel test, then codes 

that adequately predict the shadowing 

and concentration effects may be 

acceptable compliance methods. 

Foster Technology, LLC (Foster), is an 

engineering consulting firm that has 

filed a provisional patent that includes 

a methodology for detecting ice over a 

pitot inlet, providing a corrected 

airspeed, and removing ice deposits. 

Foster suggested that the FAA should 

certify its new methodology. 

We agree that existing regulations 

would allow certification of a new pitot 

probe with ice detection capability. 

However, we would certify a new pitot 

probe as part of a product’s type design 

to be approved for installation, not the 

methodology described by Foster. If 

Foster seeks independent certification of 

a new pitot probe, we suggest Foster 

complete and submit an application for 

a supplemental type certificate, at 

which time we will evaluate the new 

probe. 

Heavy Rain Requirements for Airspeed 

Indication and Angle of Attack Systems 

Airbus and EASA fully supported a 

new requirement to cover the heavy rain 

conditions being considered in the 

NPRM. Airbus commented that some 

testing at high LWCs, such as those 

proposed in the NPRM, would help to 

ensure that water drainage in rain 

conditions, especially at takeoff, is 

adequate. A private citizen commented 

that the maximum freezing rain static 

temperature under consideration would 

be unlikely to result in ice accretion and 

is not in line with figure 4 of appendix 

O. AIA, Boeing, and GAMA commented 

that the proposed expanded parameters, 

the source of which was not provided, 

do not appear congruous with hard data 

from extensive icing research. GSIS 

commented that it wanted to 

understand how the specific values for 

LWC, horizontal extent, and mean 

droplet diameter were determined and 

what the technical justifications are for 

these levels. 

We consider analysis of heavy rain 

conditions as proposed in the NPRM to 

be necessary to substantiate that water 

drainage from the airspeed indication 

and angle of attack systems is adequate. 

If the water drainage is inadequate, then 

the residual water may freeze as the 

pitot probes or angle of attack sensors 

are subjected to below freezing 

temperatures as the airplane climbs 

following takeoff. The heavy rain 

conditions are not intended as an icing 

condition as described in the NPRM. 

The heavy rain LWC is based on heavy 

rainfall data documented in MIL–STD– 

210C, Military Standard: Climatic 

Information to Determine Design and 

Test Requirements for Military Systems 


tkelley on DSK3SPTVN1PROD with RULES2
Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 65519 

13A copy of MIL–STD–210C, dated January 9, 

1987, is available in the rule Docket No. FAA– 

2010–0636. MIL–STD–210 has since been 

superseded by MIL–HDBK–310, dated June 23, 

1997, which is also available in the rule docket. 

14Both of these documents are available on the 

EASA Web site at http://www.easa.europa.eu. 

and Equipment.13 The same rain data 

was used for the AIA Propulsion 

Committee Study, Project PC 338–1 

documented in part 33, appendix B. 

Heavy rain conditions have been added 

to §§ 25.1323 and 25.1324. However, the 

conditions have been revised compared 

to the conditions proposed in the NPRM 

by removing temperature as a 

parameter. 

Applicability of the Icing Requirements 

in Part 25, Appendix O, and Part 33, 

Appendix D, to All Airspeed Indicating 

Systems 

EASA and TCCA suggested that 

§§ 25.1323 and 25.1324 be revised to 

include the icing certification of all 

external probes for flight instruments. 

EASA proposed a specific regulation 

including, but not limited to, pitot, 

pitot-static, static, angle-of-attack, 

sideslip angle, and temperature sensors. 

The regulation proposed by EASA 

would require addressing the icing 

conditions in part 25, appendix C; part 

25, appendix O; and part 33, appendix 

D. Similarly, since total air temperature 

(TAT) is an input to calculating true 

airspeed, Goodrich requested 

clarification of whether or not TAT 

sensors should be considered part of the 

airspeed indicating system when 

addressing ‘‘preventing malfunction’’ in 

part 25, appendix O, and part 33, 

appendix D, environments as described 

in § 25.1323(i). 

We do not agree with the commenters’ 

suggestions to include icing 

requirements for all external probes and 

sensors in §§ 25.1323 and 25.1324. 

Section 25.1323(i) has traditionally 

applied to pitot probes (indicated 

airspeed), and the FAA did not propose 

a change to this applicability in the 

NPRM. As such, we did not intend to 

include TAT sensors, or other externally 

mounted instrument probes in 

§ 25.1323(i). In addition, § 25.1324 was 

proposed specifically for angle-of-attack 

sensors. Revising §§ 25.1323 and 

25.1324 so that all externally mounted 

flight instrument probes and sensors 

must operate in the various icing 

conditions is beyond the scope of this 

rulemaking. We did not change the rule 

in response to these comments. 

Proposal To Add Indication System for 

External Probes 

EASA advised that some failures of 

the pitot probe heating resistance may 

not be seen by the flightcrew due to the 

low current detection system installed 

on the airplane. As a result, failure to 

provide proper pitot probe deicing may 

not be detected. EASA suggested that a 

new regulation be created to explicitly 

cover abnormal functioning of the 

heating system for externally mounted 

probes. 

We do not agree. If insufficient 

functioning of an externally mounted 

probe creates an unsafe operating 

condition, then warning information 

must be provided to the flightcrew in 

accordance with § 25.1309(c). Since we 

did not propose warning information 

specific to failure modes for certain 

externally mounted probes in the NPRM 

and the public did not have the 

opportunity to comment, we consider 

the EASA proposal to be beyond the 

scope of this rulemaking. No changes to 

the final rule have been made as a result 

of EASA’s proposal. 

Expand the Parameters for Part 33, 

Appendix D 

AIA, Boeing, and GAMA commented 

that part 33, appendix D, should be 

expanded to reflect new engine power 

loss and airspeed data loss events in ice 

crystal conditions. Appendix D is based 

on a theoretical model, and Airbus 

agreed that the conditions in appendix 

D should be applied. 

We do not agree that appendix D 

should be expanded in this final rule. 

The majority of recent airspeed data 

anomalies occurred within the altitude 

and temperature range described in part 

33, appendix D. We know of only one 

temporary loss of airspeed data event 

just outside or at the perimeter of the 

altitude and temperature range in part 

33, appendix D. Other conditions 

described in appendix D, such as what 

the ice water content actually was 

during the loss of airspeed data event, 

are unknown because it was not 

measured. We agree that appendix D is 

based on a theoretical atmospheric 

model. We are continuing to support the 

research necessary to validate the part 

33, appendix D, conditions with flight 

test data, and it would be premature to 

expand the appendix D environment at 

this time. Expansion of part 33, 

appendix D, is out of scope of the 

originally proposed rulemaking. We did 

not change appendix D based on these 

comments. 

Airbus commented that using the 

EHWG event database and referring to 

the flight distance between a TAT 

sensor anomaly and the engine event, 

one can see that almost half of the 

engine events occurred at a flight 

distance equal to or less than 10 

nautical miles from the occurrence of 

the TAT anomaly, with the majority of 

events happening within less than 4 

nautical miles. Based on these facts, 

Airbus concluded that short cloud 

exposures are the most critical. 

However, the new appendix D 

definition implies that the longest 

clouds are the most critical for engines 

and auxiliary power units (APUs), and 

adds a factor of 2 to the conservatism of 

the definitions already defined in EASA 

documents CS–E 780, Tests in IceForming Conditions, and AMC 25.1419, 

Ice Protection.14 Airbus commented that 

it is inappropriate to add an additional 

factor of 2 to the icing conditions for 

long exposures in appendix D icing 

conditions considering the uncertainty 

in the new rule. 

We do not agree. We acknowledge 

that a TAT sensor anomaly may be one 

indicator of ice crystals; however, it is 

not a very reliable indicator. The 

amount and concentration of ice crystals 

required to create a TAT sensor anomaly 

is not understood. Also, the TAT sensor 

anomaly was only present in a portion 

of the engine events in the EHWG 

database. Therefore, the TAT anomaly 

data cannot accurately show cloud 

extent. Additionally, detailed review of 

the event data indicated that once the 

TAT probe iced over enough to cause an 

indication anomaly, the engine often 

would demonstrate a power upset very 

soon after the TAT probe anomaly. This 

period of time was insufficient for the 

pilot to take action since the ice 

accretion within the engine had already 

progressed to an advanced stage. 

Therefore, we concluded that TAT 

probe anomalies are poor precursor 

indications of the ice crystal threat to 

engines, in terms of reliability of the 

indication and the time period in 

advance of power loss. When 

establishing the cloud extent factor in 

part 33, appendix D, the EHWG and 

FAA did take into account EASA CS–E– 

780 cloud definition requirements. 

However, the EHWG was not able to 

validate the analysis used to develop the 

cloud extent factor in EASA CS–E–780. 

The cloud extent factor proposed by the 

EHWG for part 33, appendix D, 

represents the most accurate cloud 

extent factor that can be established 

using the available data. No changes 

were made as a result of these 

comments. 

Snecma commented that the y-axis 

value in proposed part 33, appendix D, 

figure D3, was incorrect. The value 

should be 0.6 but the NPRM showed the 

value as zero. 

We concur. We also found that both 

the x- and y-axis values proposed in the 

NPRM were incorrect. We changed part 


tkelley on DSK3SPTVN1PROD with RULES2
65520 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 

33, appendix D, figure D3, to depict the 

correct axis values. The lowest x-axis 

value is now 1 and the lowest y-axis 

value is now 0.6. 

Several commenters noted that the 

horizontal cloud length proposed in the 

NPRM was stated in statute miles, and 

commented it should be provided in 

nautical miles. The commenters 

suggested that changing to nautical 

miles would make the distance 

measurement consistent with other 

tables and figures in appendix D. 

We agree, and changed Table 1 to 

identify that the horizontal cloud length 

is depicted in nautical miles. 

Several commenters asked why we 

included the reference to ‘‘Reference 1’’ 

in the text immediately following Table 

1 in proposed part 33, appendix D, 

especially considering the material 

constituting ‘‘Reference 1’’ was not 

identified anywhere within the NPRM. 

We agree. We removed the reference 

to ‘‘Reference 1’’ from the final rule. 

Establishing New Operating Limitations 

TCCA stated that it was not clear if 

the proposed requirements to exit all 

icing conditions were applicable only to 

in-flight icing encounters, or if they 

were also applicable to the takeoff phase 

of flight. 

We agree that clarification is needed. 

We changed § 25.1533(c) to clarify that 

the additional limitations apply to all 

phases of flight. 

Additional Requirements for Safe 

Operation 

AIA, Boeing, and GAMA commented 

that proposed appendix O, paragraph (b) 

does not define takeoff ice accretions for 

airplanes not certified for takeoff in 

appendix O conditions. Therefore, they 

suggested that § 25.207(e)(1), which 

defines stall warning requirements for 

takeoff with ice accretions, should be 

added to the list of exceptions specified 

in § 25.21(g)(3). 

We agree. We added the stall warning 

requirements in § 25.207(e)(1) to the 

exceptions listed in § 25.21(g)(3). As a 

result, applicants will not need to 

determine the stall warning margin for 

takeoff with appendix O ice accretions 

for airplanes not certified to take off in 

appendix O icing conditions. 

TCCA commented that exposure to 

appendix O icing conditions may result 

in icing accretions further aft on 

fuselage, wing and stabilizer surfaces, 

and control surfaces, beyond what 

would normally be obtained in 

appendix C conditions. Therefore, 

TCCA suggested that compliance to 

§ 25.251(b) through (e) should be shown 

for appendix O conditions. 

We proposed to retain the provision 

from Amendment 25–121 for not 

requiring compliance with § 25.251(b) 

through (e) in appendix C icing 

conditions and extend it to include 

appendix O icing conditions. Although 

Amendment 25–121 only addressed 

appendix C icing conditions, the 

conclusion that compliance to 

§ 25.251(b) through (e) need not be 

shown in icing conditions was based on 

a review of in-service experience in all 

icing conditions, not just appendix C 

icing conditions. Therefore, including 

§ 25.251(b) through (e) within the 

exceptions listed in § 25.21(g) for 

certifications is equally applicable to 

either appendix C or appendix O 

conditions. No changes were made to 

the final rule as a result of this 

comment. 

Dassault commented that the 

proposed ice accretion definitions in 

part II of appendix O did not include an 

ice accretion specific to the flight phase 

covered by § 25.121(a). Dassault added 

that the ice accretion used for showing 

compliance with § 25.121(a)(1) should 

be the accretion occurring between 

liftoff and the point at which the 

landing gear is fully retracted. Dassault 

requested that the FAA add the 

following definition: ‘‘Takeoff—landing 

gear extended ice is the most critical ice 

accretion on unprotected surfaces, and 

any ice accretion on protected surfaces 

appropriate to normal ice protection 

system operation, occurring between 

liftoff and the point at which the 

landing gear is fully retracted, assuming 

accretion starts at liftoff in the icing 

conditions defined in Part I of this 

appendix.’’ 

Instead of adding a definition for the 

ice accretion during the initial takeoff 

segment covered by § 25.121(a), we have 

reconsidered this issue and determined 

that this flight segment does not last 

long enough for significant ice 

accretions to occur, even in appendix O 

icing conditions. Therefore, we added 

§ 25.121(a) to the list of requirements in 

§ 25.21(g)(4) that do not have to be met 

with appendix O ice accretions. We also 

agree that our proposed definition for 

takeoff ice was inadequate. We did not 

intend to require that applicants include 

the small effect (if any) of ice accretion 

from the point of liftoff to the end of the 

takeoff distance in determining the 

takeoff distance under § 25.113, which 

the appendix C definition and the 

proposed appendix O definition may 

have implied. Therefore, we revised the 

definitions of takeoff ice and final 

takeoff ice in part 25, appendix C and 

appendix O, such that the ice accretion 

begins at the end of the takeoff distance, 

not at the point of liftoff. This change 

better aligns the definition of the takeoff 

and final takeoff ice with that of the 

takeoff path used for determining 

takeoff performance under §§ 25.111, 

25.113, and 25.115. 

Request To Revise § 25.629 

TCCA commented that for airplanes 

exempt from § 25.1420, no evaluation of 

aeroelastic stability is required in 

appendix O icing conditions. For that 

reason, TCCA recommended that all 

icing considerations be included 

directly in § 25.629. 

We do not agree. Section 25.629(b)(1) 

requires aeroelastic stability evaluations 

of the airplane in normal conditions. 

For airplanes approved for operation in 

icing conditions, ice accumulations are 

considered a normal condition under 

the rule. Since § 25.629 does not 

specifically distinguish between various 

types of icing conditions, all icing 

conditions for which the airplane is 

approved are considered normal 

conditions. For airplanes exempt from 

§ 25.1420, or for which approval is not 

sought for flight in appendix O icing 

conditions, § 25.629(d)(3) requires that 

ice accumulations due to inadvertent 

icing encounters must be considered for 

airplanes not approved for operation in 

icing conditions. The intent is to 

consider ice accumulations due to 

inadvertent icing encounters from any 

icing conditions for which the airplane 

is not approved, including appendix O 

conditions. We did not change the rule 

as a result of this comment. 

Miscellaneous Issues 

After the FAA issued the NPRM to 

this rulemaking, we issued a final rule 

for Harmonization of Various 

Airworthiness Standards for Transport 

Category Airplanes—Flight Rules 

(docket number FAA–2010–0310). That 

final rule revised § 25.21(g)(1) to add the 

requirement that the stall warning 

margin requirements of § 25.207(c) and 

(d) must be met in the landing 

configuration in the icing conditions of 

appendix C. That final rule also revised 

§ 25.253(c) to define the maximum 

speeds at which the static lateraldirectional stability requirements of 

§ 25.177(a) through (c) and the 

directional and lateral control 

requirements of § 25.147(f) must be met 

in the icing conditions of appendix C. 

We have retained those changes in 

§§ 25.21(g)(2) and 25.253(c) of this final 

rule. For consistency, we also revised 

§ 25.21(g)(4) to require that § 25.207(c) 

and (d) must be met in the landing 

configuration in the appendix O icing 

conditions for which certification is 

sought. This revision is a logical 

outgrowth of the notice in this 


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Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 65521 

15This document can be found at http://

www.faa.gov/other_visit/aviation_industry/airline_

operators/airline_safety/safo/all_safos/media/2010/

SAFO10012.pdf. 

16A copy of the charter is available at http://

www.faa.gov/about/office_org/headquarters_

offices/avs/offices/afs/afs200/media/208_ARC_

Charter.pdf. 

rulemaking because the purpose of 

§ 25.21(g)(4) is to ensure safe operation 

in appendix O conditions during all 

phases of flight, including the landing 

phase. 

The FAA finds that clarifying the 

applicability of the proposed icing 

conditions to APU installations is 

necessary. Section 25.901(d) currently 

requires that each auxiliary power unit 

installation must meet the applicable 

provisions of the subpart. This 

requirement is unchanged by this 

rulemaking. The FAA considers 

§ 25.1093(b) to be applicable to APU 

installations because they are turbine 

engines. An essential APU is used to 

provide air and/or power necessary to 

maintain safe airplane operation. A nonessential APU is used to provide air 

and/or power as a matter of convenience 

and may be shutdown without 

jeopardizing safe airplane operation. 

The FAA has traditionally required that 

essential APU installations continue to 

operate in part 25, appendix C, icing 

conditions. Non-essential APU 

installations either have restricted 

operation or are required to demonstrate 

that operation in icing conditions does 

not affect the safe operation of the 

airplane. References to part 25, 

appendix O, and part 33, appendix D, 

have been added to § 25.1093(b). 

As previously discussed, the 

applicability of appendix O conditions 

in § 25.1093(b) excludes all turbine 

engine installations that are used on 

airplanes with a MTOW equal to or 

greater than 60,000 pounds. The FAA 

still considers APUs to be turbine 

engines that must comply with the 

installation requirements in §§ 25.901 

and 25.1093; therefore, this rulemaking 

is not creating separate requirements for 

APU installations. Essential APU 

installations must continue to operate in 

the icing conditions applicable under 

§ 25.1093(b). Non-essential APU 

installations must not affect the safe 

operation of the airplane when the icing 

conditions applicable under 

§ 25.1093(b) are inadvertently 

encountered. 

Also as previously discussed, the 

applicability of appendix O conditions 

in § 25.1093(b) was revised to provide 

relief for larger airplanes because of the 

successful in-service history of existing 

larger airplane and larger airplane 

turbine engine inlet designs. If future 

APU installations contain novel or 

unusual design features that affect this 

successful in-service history, and those 

design features make the airplane more 

susceptible to the effects of flight in SLD 

icing conditions, the FAA can issue 

special conditions to provide adequate 

safety standards. 

A private citizen identified potential 

flightcrew training issues associated 

with this rulemaking. The commenter 

noted that while practical test standards 

for post-stall recovery procedures are 

clearly related to icing safety, they are 

not regulatory and may be changed 

without formal notice. The commenter 

also remarked that a common pilot 

input characteristic to add power and 

maintain the pitch angle of the airplane 

has been observed on the flight data 

recorder time histories related to several 

icing related accidents. In some cases, 

nose up pitch input was applied even 

against the nose down force being 

applied by the airplane’s ‘‘stick pusher’’ 

that is designed to rapidly reduce the 

angle of attack. The commenter noted 

that these habit patterns are developed 

and reinforced as the required response 

in simulator training in accordance with 

FAA practical test standards for stall 

identification and recovery for 

minimum altitude loss. For example, 

‘‘Minimum altitude loss’’ is trained as 

‘‘zero altitude loss.’’ 

The flightcrew training issues 

addressed by the commenter are 

important safety considerations. 

However, flightcrew training is beyond 

the scope of this rulemaking because 

this rulemaking addresses design 

requirements. On July 6, 2010, the FAA 

published Safety Alert for Operators 

(SAFO) 10012. The SAFO discusses the 

possible misinterpretation of the 

practical test standards language 

‘‘minimal loss of altitude.’’ 15

In addition, on September 30, 2010, 

the FAA established the Stick Pusher 

and Adverse Weather Event Training 

Aviation Rulemaking Committee. One of 

the rulemaking committee objectives is 

to identify the best goals, procedures, 

and training practices that will enable 

air carrier pilots to accurately and 

consistently respond to unexpected 

stick pusher activations, icing 

conditions, and microburst and 

windshear events.16 The ARC has 

submitted recommendations to the 

FAA, which are being considered for 

additional rulemaking activities. Such 

activities are beyond the scope of this 

rulemaking. 

Regulatory Notices and Analyses 

Regulatory Evaluation 

Changes to Federal regulations must 

undergo several economic analyses. 

First, Executive Order 12866 and 

Executive Order 13563 direct that each 

Federal agency shall propose or adopt a 

regulation only upon a reasoned 

determination that the benefits of the 

intended regulation justify its costs. 

Second, the Regulatory Flexibility Act 

of 1980 (Pub. L. 96–354) requires 

agencies to analyze the economic 

impact of regulatory changes on small 

entities. Third, the Trade Agreements 

Act (Pub. L. 96–39) prohibits agencies 

from setting standards that create 

unnecessary obstacles to the foreign 

commerce of the United States. In 

developing U.S. standards, this Trade 

Act requires agencies to consider 

international standards and, where 

appropriate, that they be the basis of 

U.S. standards. Fourth, the Unfunded 

Mandates Reform Act of 1995 (Pub. L. 

104–4) requires agencies to prepare a 

written assessment of the costs, benefits, 

and other effects of proposed or final 

rules that include a Federal mandate 

likely to result in the expenditure by 

State, local, or tribal governments, in the 

aggregate, or by the private sector, of 

$100 million or more annually (adjusted 

for inflation with base year of 1995). 

This portion of the preamble 

summarizes the FAA’s analysis of the 

economic impacts of this final rule. We 

suggest readers seeking greater detail 

read the full regulatory evaluation, a 

copy of which we have placed in the 

docket for this rulemaking. 

In conducting these analyses, the FAA 

has determined that this final rule: (1) 

Has benefits that justify its costs, (2) is 

not an economically ‘‘significant 

regulatory action’’ as defined in section 

3(f) of Executive Order 12866, (3) is ‘‘not 

significant’’ as defined in DOT’s 

Regulatory Policies and Procedures; (4) 

will not have a significant economic 

impact on a substantial number of small 

entities; (5) will not create unnecessary 

obstacles to the foreign commerce of the 

United States; and (6) will not impose 

an unfunded mandate on state, local, or 

tribal governments, or on the private 

sector by exceeding the threshold 

identified above. These analyses are 

summarized below. 

Total Benefits and Costs of This Final 

Rule 


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TABLE 1—TOTAL BENEFITS AND COSTS OF THIS RULE

2012$ 7% Present value 

Benefit Cost Benefit Cost 

Part 33 Engines ............................................................................. Qualitative ......... $13,936,000 Qualitative ........ $11,375,927 

Large Part 25 Airplanes ................................................................. $362,319,857 ... 14,126,333 $76,861,295 ..... 11,531,295 

Other Part 25 Airplanes ................................................................. $220,570,582 ... 33,198,788 $50,028,650 ..... 19,385,401 

Total ........................................................................................ $582,890,439 ... 61,261,121 $126,889,985 ... 42,292,624 

* Details may not add to row or column totals due to rounding. 

Persons Potentially Affected by This 

Final Rule 

Part 25 airplane manufacturers, 

Engine manufacturers, and 

Operators of affected equipment. 

Assumptions 

The deliveries and affected fleets are 

analyzed over appropriate time periods 

and are customized based upon actual 

historical data. The fleet development is 

customized to the various (and 

different) airplane types. We 

conservatively assume that all 

certifications will occur in 2015 and 

deliveries will occur in the following 

year. As production time spans differ by 

size of airplane, it is important for the 

reader to focus on present value benefits 

and costs. 

Present Value Discount rate—7% 

Value of an Averted Fatality—$9.1 

million in 2012 

Both Costs and Benefits are expressed 

in 2012 dollars. 

Benefits of This Final Rule 

The FAA has analyzed events that 

would have been prevented if this final 

rule were in place at the time of 

certification. The events were evaluated 

for applicability and preventability in 

context with the requirements contained 

in this final rule. 

For the categories of airplanes, first, 

we develop casualty rates for fatalities, 

injuries, investigations, and destroyed 

airplanes based on historical ice-related 

accidents. Next, we multiply the total 

annual affected airplanes by the annual 

risk per airplane. Lastly, we multiply 

the casualty rates by the projected 

number of part 25 newly certificated 

deliveries. When summed over time, the 

total estimated benefits are shown in 

Table 1. 

Viewed from a breakeven analysis 

using only preventable fatalities, with 

each fatality valued at $9.1 million, this 

rule has benefits exceeding costs with 

only 7 fatalities prevented. 

Costs of This Final Rule 

The total estimated costs are shown in 

Table 1. We obtained the basis of our 

cost estimates from the industry. Since 

the NPRM, we have modified the 

estimates based upon industry 

comments and clarifications to those 

comments. The compliance costs are 

analyzed in context of the part 25 and 

part 33 certification requirements. 

As summarized in Table 2, the cost 

categories in the regulatory evaluation 

incorporate both certification and 

operational costs. We analyze each cost 

category separately. The cost categories 

in this evaluation are the same as those 

provided by industry to comply with 

the requirements contained in this rule. 

TABLE 2—COST SUMMARY

Nominal cost 7% PV cost 

Engine Certification Cost ............................................................................................................................. $7,936,000 $6,478,140 

Engine Capital Cost ..................................................................................................................................... 6,000,000 4,897,787 

Total Engine Cost ................................................................................................................................. 13,936,000 11,375,927 

New Large Airplane Certification Cost ........................................................................................................ 14,126,333 11,531,295 

Large Airplane Hardware Cost .................................................................................................................... 0 0 

Large Airplane Fuel Cost ............................................................................................................................. 0 0 

Total Large Airplane Cost .................................................................................................................... 14,126,333 11,531,295 

Other Airplane Certification Cost ................................................................................................................. 19,066,026 15,563,557 

Other Airplane Hardware Cost .................................................................................................................... 2,475,000 1,312,609 

Other Airplane Fuel Burn Cost .................................................................................................................... 11,657,762 2,509,236 

Total Other Airplane Costs ................................................................................................................... 33,198,788 19,385,401 

Total Costs .................................................................................................................................... 61,261,121 42,292,624 

* Details may not add to row or column totals due to rounding. 

Alternatives Considered 

Alternative 1—Make the entire rule 

applicable to all airplanes. 

Not all the requirements in this rule 

extend to large transport category 

airplanes (those with a MTOW greater 

than 60,000 pounds). Under this 

alternative, the proposed design 

requirements would extend to all 

transport category airplanes. This 

alternative was rejected because this 

alternative would add significant costs 

without a commensurate increase in 

benefits. 

Alternative 2—Limit the scope of 

applicability to small transport category 

airplanes. 

Although this alternative would 

decrease the estimated cost, the FAA 

believes that medium and large 

airplanes are at risk of an SLD icing 


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Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 65523 

event. The FAA does not want a 

significant proportion of the future fleet 

to be disproportionately at risk. 

Regulatory Flexibility Determination 

The Regulatory Flexibility Act of 1980 

(Pub. L. 96–354) (RFA) establishes as a 

principle of regulatory issuance that 

agencies shall endeavor, consistent with 

the objectives of the rule and of 

applicable statutes, to fit regulatory and 

informational requirements to the scale 

of the businesses, organizations, and 

governmental jurisdictions subject to 

regulation. To achieve this principle, 

agencies are required to solicit and 

consider flexible regulatory proposals 

and to explain the rationale for their 

actions to assure that such proposals are 

given serious consideration. The RFA 

covers a wide-range of small entities, 

including small businesses, not-forprofit organizations, and small 

governmental jurisdictions. 

Agencies must perform a review to 

determine whether a rule will have a 

significant economic impact on a 

substantial number of small entities. If 

the agency determines that it will, the 

agency must prepare a regulatory 

flexibility analysis as described in the 

RFA. 

However, if an agency determines that 

a rule is not expected to have a 

significant economic impact on a 

substantial number of small entities, 

section 605(b) of the RFA provides that 

the head of the agency may so certify 

and a regulatory flexibility analysis is 

not required. The certification must 

include a statement providing the 

factual basis for this determination, and 

the reasoning should be clear. Our 

initial determination was that the 

proposed rule would not have a 

significant economic impact on a 

substantial number of small entities. We 

received no public comments regarding 

our initial determination. As such, this 

final rule will not have a significant 

economic impact on a substantial 

number of small entities for the 

following reasons. 

Airplane and Engine Manufacturers 

Airplane and engine manufacturers 

will be affected by the requirements 

contained in this rule. 

For airplane manufacturers, we use 

the size standards from the Small 

Business Administration for Air 

Transportation and Aircraft 

Manufacturing specifying companies 

having less than 1,500 employees as 

small entities. The current United States 

part 25 airplane manufacturers include 

Boeing, Cessna Aircraft, Gulfstream 

Aerospace, Learjet (owned by 

Bombardier), Lockheed Martin, 

Raytheon Aircraft, and Sabreliner 

Corporation. Because all U.S. transportcategory airplane manufacturers have 

more than 1,500 employees, none are 

considered small entities. 

United States aircraft engine 

manufacturers include General Electric, 

CFM International, Pratt & Whitney, 

International Aero Engines, Rolls-Royce 

Corporation, Honeywell, and Williams 

International. All but one exceeds the 

Small Business Administration smallentity criteria for aircraft engine 

manufacturers. Williams International is 

the only one of these manufacturers that 

is a U.S. small business. 

The FAA estimated that Williams 

International engines power 

approximately four percent of the 

engines on active U.S. airplanes. 

Assuming that future deliveries of 

newly certificated airplanes with 

Williams International engines will 

have the same percentage as the active 

fleet, we calculated that this final rule 

will add about 0.2 percent of their 

annual revenue. We do not consider a 

cost of 0.2 percent of annual revenue 

significant. 

Operators 

In addition to the certification cost 

incurred by manufacturers, operators 

will incur fuel costs due to the 

estimated additional impact of weight 

changes from equipment on affected 

airplanes. On average, operators affected 

by the final rule will incur no additional 

annual fuel costs for newly certificated 

large part 25 airplanes, and $189, in 

present value, in additional fuel costs 

for other newly certificated part 25 

airplanes. This final rule will apply to 

airplanes that have yet to be designed; 

there will be no immediate cost to small 

entities. The other airplane annual fuel 

cost of $189, in present value, is not 

significant in terms of total operating 

expenses. We do not consider these 

annual fuel costs a significant economic 

impact. 

This final rule will not have a 

significant economic impact on a 

substantial number of airplane 

manufacturers, engine manufacturers, or 

operators. Therefore, as the FAA 

Administrator, I certify that this rule 

will not have a significant economic 

impact on a substantial number of small 

entities. 

International Trade Analysis 

The Trade Agreements Act of 1979 

(Pub. L. 96–39), as amended by the 

Uruguay Round Agreements Act (Pub. 

L. 103–465), prohibits Federal agencies 

from establishing standards or engaging 

in related activities that create 

unnecessary obstacles to the foreign 

commerce of the United States. 

Pursuant to these Acts, the 

establishment of standards is not 

considered an unnecessary obstacle to 

the foreign commerce of the United 

States, so long as the standard has a 

legitimate domestic objective, such as 

the protection of safety, and does not 

operate in a manner that excludes 

imports that meet this objective. The 

statute also requires consideration of 

international standards and, where 

appropriate, that they be the basis for 

U.S. standards. 

The FAA has assessed the effect of 

this final rule and determined that it 

will not be an unnecessary obstacle to 

the foreign commerce of the United 

States as the purpose of this rule is to 

ensure aviation safety. 

Unfunded Mandates Assessment 

Title II of the Unfunded Mandates 

Reform Act of 1995 (Pub. L. 104–4) 

requires each Federal agency to prepare 

a written statement assessing the effects 

of any Federal mandate in a proposed or 

final agency rule that may result in an 

expenditure of $100 million or more (in 

1995 dollars) in any one year by State, 

local, and tribal governments, in the 

aggregate, or by the private sector; such 

a mandate is deemed to be a ‘‘significant 

regulatory action.’’ The FAA currently 

uses an inflation-adjusted value of 

$143.1 million in lieu of $100 million. 

This final rule does not contain such a 

mandate; therefore, the requirements of 

Title II do not apply. 

Paperwork Reduction Act 

The Paperwork Reduction Act of 1995 

(44 U.S.C. 3507(d)) requires that the 

FAA consider the impact of paperwork 

and other information collection 

burdens imposed on the public. The 

information collection requirements 

associated with this final rule have been 

previously approved by the Office of 

Management and Budget (OMB) under 

the provisions of the Paperwork 

Reduction Act of 1995 (44 U.S.C. 

3507(d)) and have been assigned OMB 

Control Number 2120–0018. 

International Compatibility and 

Cooperation 

(1) In keeping with U.S. obligations 

under the Convention on International 

Civil Aviation, it is FAA policy to 

conform to International Civil Aviation 

Organization (ICAO) Standards and 

Recommended Practices to the 

maximum extent practicable. The FAA 

has reviewed the corresponding ICAO 

Standards and Recommended Practices 

and has identified no differences with 

these regulations. 


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65524 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 

(2) Executive Order 13609, Promoting 

International Regulatory Cooperation, 

promotes international regulatory 

cooperation to meet shared challenges 

involving health, safety, labor, security, 

environmental, and other issues and to 

reduce, eliminate, or prevent 

unnecessary differences in regulatory 

requirements. The FAA has analyzed 

this action under the policies and 

agency responsibilities of Executive 

Order 13609, and has determined that 

this action will have no effect on 

international regulatory cooperation. 

Environmental Analysis 

FAA Order 1050.1E identifies FAA 

actions that are categorically excluded 

from preparation of an environmental 

assessment or environmental impact 

statement under the National 

Environmental Policy Act in the 

absence of extraordinary circumstances. 

The FAA has determined this 

rulemaking action qualifies for the 

categorical exclusion identified in 

paragraph 4(j) and involves no 

extraordinary circumstances. 

Regulations Affecting Intrastate 

Aviation in Alaska 

Section 1205 of the FAA 

Reauthorization Act of 1996 (110 Stat. 

3213) requires the FAA, when 

modifying its regulations in a manner 

affecting intrastate aviation in Alaska, to 

consider the extent to which Alaska is 

not served by transportation modes 

other than aviation, and to establish 

appropriate regulatory distinctions. In 

the NPRM, the FAA requested 

comments on whether the proposed rule 

should apply differently to intrastate 

operations in Alaska. The agency did 

not receive any comments, and has 

determined, based on the administrative 

record of this rulemaking, that there is 

no need to make any regulatory 

distinctions applicable to intrastate 

aviation in Alaska. 

Executive Order Determinations 

Executive Order 13132, Federalism 

The FAA has analyzed this final rule 

under the principles and criteria of 

Executive Order 13132, Federalism. The 

agency determined that this action will 

not have a substantial direct effect on 

the States, or the relationship between 

the Federal Government and the States, 

or on the distribution of power and 

responsibilities among the various 

levels of government, and, therefore, 

does not have Federalism implications. 

Executive Order 13211, Regulations 

That Significantly Affect Energy Supply, 

Distribution, or Use 

The FAA analyzed this final rule 

under Executive Order 13211, Actions 

Concerning Regulations that 

Significantly Affect Energy Supply, 

Distribution, or Use (May 18, 2001). The 

agency has determined that it is not a 

‘‘significant energy action’’ under the 

executive order and it is not likely to 

have a significant adverse effect on the 

supply, distribution, or use of energy. 

How To Obtain Additional Information 

Rulemaking Documents 

An electronic copy of a rulemaking 

document may be obtained by using the 

Internet— 

1. Search the Federal eRulemaking 

Portal (http://www.regulations.gov); 

2. Visit the FAA’s Regulations and 

Policies Web page at http:// 

www.faa.gov/regulations_policies/ or 

3. Access the Government Printing 

Office’s Web page at http:// 

www.gpo.gov/fdsys/browse/ 

collection.action?collectionCode=FR. 

Copies may also be obtained by 

sending a request (identified by notice, 

amendment, or docket number of this 

rulemaking) to the Federal Aviation 

Administration, Office of Rulemaking, 

ARM–1, 800 Independence Avenue 

SW., Washington, DC 20591, or by 

calling (202) 267–9680. 

Comments Submitted to the Docket 

Comments received may be viewed by 

going to http://www.regulations.gov and 

following the online instructions to 

search the docket number for this 

action. Anyone is able to search the 

electronic form of all comments 

received into any of the FAA’s dockets 

by the name of the individual 

submitting the comment (or signing the 

comment, if submitted on behalf of an 

association, business, labor union, etc.). 

Small Business Regulatory Enforcement 

Fairness Act 

The Small Business Regulatory 

Enforcement Fairness Act (SBREFA) of 

1996 requires FAA to comply with 

small entity requests for information or 

advice about compliance with statutes 

and regulations within its jurisdiction. 

A small entity with questions regarding 

this document, may contact its local 

FAA official, or the person listed under 

the FOR FURTHER INFORMATION CONTACT

heading at the beginning of the 

preamble. To find out more about 

SBREFA on the Internet, visit http:// 

www.faa.gov/regulations_policies/ 

rulemaking/sbre_act/. 

List of Subjects 

14 CFR Part 25 

Aircraft, Aviation safety, Reporting 

and recordkeeping requirements, Safety, 

Transportation. 

14 CFR Part 33 

Aircraft, Aviation safety. 

The Amendment 

In consideration of the foregoing, the 

Federal Aviation Administration 

amends chapter I of title 14, Code of 

Federal Regulations as follows: 

PART 25—AIRWORTHINESS 

STANDARDS: TRANSPORT 

CATEGORY AIRPLANES 

■ 1. The authority citation for part 25 

continues to read as follows: 

Authority: 49 U.S.C. 106(g), 40113, 44701, 

44702 and 44704. 

■ 2. Amend § 25.21 by revising 

paragraphs (g)(1) and (2) and adding 

paragraphs (g)(3) and (4) to read as 

follows: 

§ 25.21 Proof of compliance. 

* * * * * 

(g) * * * 

(1) Paragraphs (g)(3) and (4) of this 

section apply only to airplanes with one 

or both of the following attributes: 

(i) Maximum takeoff gross weight is 

less than 60,000 lbs; or 

(ii) The airplane is equipped with 

reversible flight controls. 

(2) Each requirement of this subpart, 

except §§ 25.121(a), 25.123(c), 

25.143(b)(1) and (2), 25.149, 

25.201(c)(2), 25.239, and 25.251(b) 

through (e), must be met in the icing 

conditions specified in Appendix C of 

this part. Section 25.207(c) and (d) must 

be met in the landing configuration in 

the icing conditions specified in 

Appendix C, but need not be met for 

other configurations. Compliance must 

be shown using the ice accretions 

defined in part II of Appendix C of this 

part, assuming normal operation of the 

airplane and its ice protection system in 

accordance with the operating 

limitations and operating procedures 

established by the applicant and 

provided in the airplane flight manual. 

(3) If the applicant does not seek 

certification for flight in all icing 

conditions defined in Appendix O of 

this part, each requirement of this 

subpart, except §§ 25.105, 25.107, 

25.109, 25.111, 25.113, 25.115, 25.121, 

25.123, 25.143(b)(1), (b)(2), and (c)(1), 

25.149, 25.201(c)(2), 25.207(c), (d), and 

(e)(1), 25.239, and 25.251(b) through (e), 

must be met in the Appendix O icing 

conditions for which certification is not 


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sought in order to allow a safe exit from 

those conditions. Compliance must be 

shown using the ice accretions defined 

in part II, paragraphs (b) and (d) of 

Appendix O, assuming normal 

operation of the airplane and its ice 

protection system in accordance with 

the operating limitations and operating 

procedures established by the applicant 

and provided in the airplane flight 

manual. 

(4) If the applicant seeks certification 

for flight in any portion of the icing 

conditions of Appendix O of this part, 

each requirement of this subpart, except 

§§ 25.121(a), 25.123(c), 25.143(b)(1) and 

(2), 25.149, 25.201(c)(2), 25.239, and 

25.251(b) through (e), must be met in 

the Appendix O icing conditions for 

which certification is sought. Section 

25.207(c) and (d) must be met in the 

landing configuration in the Appendix 

O icing conditions for which 

certification is sought, but need not be 

met for other configurations. 

Compliance must be shown using the 

ice accretions defined in part II, 

paragraphs (c) and (d) of Appendix O, 

assuming normal operation of the 

airplane and its ice protection system in 

accordance with the operating 

limitations and operating procedures 

established by the applicant and 

provided in the airplane flight manual. 

■ 3. Amend § 25.105 by revising 

paragraph (a)(2) introductory text to 

read as follows: 

§ 25.105 Takeoff. 

(a) * * * 

(2) In icing conditions, if in the 

configuration used to show compliance 

with § 25.121(b), and with the most 

critical of the takeoff ice accretion(s) 

defined in Appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g): 

* * * * * 

■ 4. Amend § 25.111 by revising 

paragraphs (c)(5)(i) and (ii) to read as 

follows: 

§ 25.111 Takeoff path. 

* * * * * 

(c) * * * 

(5) * * * 

(i) With the most critical of the takeoff 

ice accretion(s) defined in Appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), from a 

height of 35 feet above the takeoff 

surface up to the point where the 

airplane is 400 feet above the takeoff 

surface; and 

(ii) With the most critical of the final 

takeoff ice accretion(s) defined in 

Appendices C and O of this part, as 

applicable, in accordance with 

§ 25.21(g), from the point where the 

airplane is 400 feet above the takeoff 

surface to the end of the takeoff path. 

* * * * * 

■ 5. Amend § 25.119 by revising 

paragraph (b) to read as follows: 

§ 25.119 Landing climb: All-enginesoperating. 

* * * * * 

(b) In icing conditions with the most 

critical of the landing ice accretion(s) 

defined in Appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g), and with a climb speed of 

VREF determined in accordance with 

§ 25.125(b)(2)(ii). 

■ 6. Amend § 25.121 by revising 

paragraphs (b)(2)(ii) introductory text, 

(c)(2)(ii) introductory text, and (d)(2)(ii) 

to read as follows: 

§ 25.121 Climb: One-engine-inoperative. 

* * * * * 

(b) * * * 

(2) * * * 

(ii) In icing conditions with the most 

critical of the takeoff ice accretion(s) 

defined in Appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g), if in the configuration used to 

show compliance with § 25.121(b) with 

this takeoff ice accretion: 

* * * * * 

(c) * * * 

(2) * * * 

(ii) In icing conditions with the most 

critical of the final takeoff ice 

accretion(s) defined in Appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), if in the 

configuration used to show compliance 

with § 25.121(b) with the takeoff ice 

accretion used to show compliance with 

§ 25.111(c)(5)(i): 

* * * * * 

(d) * * * 

(2) * * * 

(ii) In icing conditions with the most 

critical of the approach ice accretion(s) 

defined in Appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g). The climb speed selected for 

non-icing conditions may be used if the 

climb speed for icing conditions, 

computed in accordance with paragraph 

(d)(1)(iii) of this section, does not 

exceed that for non-icing conditions by 

more than the greater of 3 knots CAS or 

3 percent. 

■ 7. Amend § 25.123 by revising 

paragraph (b)(2) introductory text to 

read as follows: 

§ 25.123 En route flight paths. 

* * * * * 

(b) * * * 

(2) In icing conditions with the most 

critical of the en route ice accretion(s) 

defined in Appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g), if: 

* * * * * 

■ 8. Amend § 25.125 by revising 

paragraphs (a)(2), (b)(2)(ii)(B), and 

(b)(2)(ii)(C) to read as follows: 

§ 25.125 Landing. 

(a) * * * 

(2) In icing conditions with the most 

critical of the landing ice accretion(s) 

defined in Appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g), if VREF for icing conditions 

exceeds VREF for non-icing conditions 

by more than 5 knots CAS at the 

maximum landing weight. 

(b) * * * 

(2) * * * 

(ii) * * * 

(B) 1.23 VSR0 with the most critical of 

the landing ice accretion(s) defined in 

Appendices C and O of this part, as 

applicable, in accordance with 

§ 25.21(g), if that speed exceeds VREF

selected for non-icing conditions by 

more than 5 knots CAS; and 

(C) A speed that provides the 

maneuvering capability specified in 

§ 25.143(h) with the most critical of the 

landing ice accretion(s) defined in 

Appendices C and O of this part, as 

applicable, in accordance with 

§ 25.21(g). 

* * * * * 

■ 9. Amend § 25.143 by revising 

paragraphs (c) introductory text, (i)(1), 

and (j) introductory text to read as 

follows: 

§ 25.143 General. 

* * * * * 

(c) The airplane must be shown to be 

safely controllable and maneuverable 

with the most critical of the ice 

accretion(s) appropriate to the phase of 

flight as defined in Appendices C and 

O of this part, as applicable, in 

accordance with § 25.21(g), and with the 

critical engine inoperative and its 

propeller (if applicable) in the minimum 

drag position: 

* * * * * 

(i) * * * 

(1) Controllability must be 

demonstrated with the most critical of 

the ice accretion(s) for the particular 

flight phase as defined in Appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g); 

* * * * * 

(j) For flight in icing conditions before 

the ice protection system has been 

activated and is performing its intended 

function, it must be demonstrated in 

flight with the most critical of the ice 

accretion(s) defined in Appendix C, part 


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II, paragraph (e) of this part and 

Appendix O, part II, paragraph (d) of 

this part, as applicable, in accordance 

with § 25.21(g), that: 

* * * * * 

■ 10. Amend § 25.207 by revising 

paragraphs (b), (e)(1), (e)(2), (e)(3), (e)(4), 

(e)(5), and (h) introductory text as 

follows: 

§ 25.207 Stall warning. 

* * * * * 

(b) The warning must be furnished 

either through the inherent aerodynamic 

qualities of the airplane or by a device 

that will give clearly distinguishable 

indications under expected conditions 

of flight. However, a visual stall warning 

device that requires the attention of the 

crew within the cockpit is not 

acceptable by itself. If a warning device 

is used, it must provide a warning in 

each of the airplane configurations 

prescribed in paragraph (a) of this 

section at the speed prescribed in 

paragraphs (c) and (d) of this section. 

Except for the stall warning prescribed 

in paragraph (h)(3)(ii) of this section, the 

stall warning for flight in icing 

conditions must be provided by the 

same means as the stall warning for 

flight in non-icing conditions. 

* * * * * 

(e) * * * 

(1) The most critical of the takeoff ice 

and final takeoff ice accretions defined 

in Appendices C and O of this part, as 

applicable, in accordance with 

§ 25.21(g), for each configuration used 

in the takeoff phase of flight; 

(2) The most critical of the en route 

ice accretion(s) defined in Appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), for the en 

route configuration; 

(3) The most critical of the holding ice 

accretion(s) defined in Appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), for the 

holding configuration(s); 

(4) The most critical of the approach 

ice accretion(s) defined in Appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), for the 

approach configuration(s); and 

(5) The most critical of the landing ice 

accretion(s) defined in Appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), for the 

landing and go-around configuration(s). 

* * * * * 

(h) The following stall warning 

margin is required for flight in icing 

conditions before the ice protection 

system has been activated and is 

performing its intended function. 

Compliance must be shown using the 

most critical of the ice accretion(s) 

defined in Appendix C, part II, 

paragraph (e) of this part and Appendix 

O, part II, paragraph (d) of this part, as 

applicable, in accordance with 

§ 25.21(g). The stall warning margin in 

straight and turning flight must be 

sufficient to allow the pilot to prevent 

stalling without encountering any 

adverse flight characteristics when: 

* * * * * 

■ 11. Amend § 25.237 by revising 

paragraph (a)(3)(ii) to read as follows: 

§ 25.237 Wind velocities. 

(a) * * * 

(3) * * * 

(ii) Icing conditions with the most 

critical of the landing ice accretion(s) 

defined in Appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g). 

* * * * * 

■ 12. Amend § 25.253 by revising 

paragraph (c) introductory text to read 

as follows: 

§ 25.253 High-speed characteristics. 

* * * * * 

(c) Maximum speed for stability 

characteristics in icing conditions. The 

maximum speed for stability 

characteristics with the most critical of 

the ice accretions defined in 

Appendices C and O of this part, as 

applicable, in accordance with 

§ 25.21(g), at which the requirements of 

§§ 25.143(g), 25.147(f), 25.175(b)(1), 

25.177(a) through (c), and 25.181 must 

be met, is the lower of: 

* * * * * 

■ 13. Amend § 25.773 by revising 

paragraph (b)(1)(ii) to read as follows: 

§ 25.773 Pilot compartment view. 

* * * * * 

(b) * * * 

(1) * * * 

(ii) The icing conditions specified in 

Appendix C of this part and the 

following icing conditions specified in 

Appendix O of this part, if certification 

for flight in icing conditions is sought: 

(A) For airplanes certificated in 

accordance with § 25.1420(a)(1), the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(B) For airplanes certificated in 

accordance with § 25.1420(a)(2), the 

icing conditions that the airplane is 

certified to safely operate in and the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(C) For airplanes certificated in 

accordance with § 25.1420(a)(3) and for 

airplanes not subject to § 25.1420, all 

icing conditions. 

* * * * * 

■ 14. Amend § 25.903 by adding a new 

paragraph (a)(3) to read as follows: 

§ 25.903 Engines. 

(a) * * * 

(3) Each turbine engine must comply 

with one of the following paragraphs: 

(i) Section 33.68 of this chapter in 

effect on January 5, 2015, or as 

subsequently amended; or 

(ii) Section 33.68 of this chapter in 

effect on February 23, 1984, or as 

subsequently amended before January 5, 

2015, unless that engine’s ice 

accumulation service history has 

resulted in an unsafe condition; or 

(iii) Section 33.68 of this chapter in 

effect on October 1, 1974, or as 

subsequently amended prior to February 

23, 1984, unless that engine’s ice 

accumulation service history has 

resulted in an unsafe condition; or 

(iv) Be shown to have an ice 

accumulation service history in similar 

installation locations which has not 

resulted in any unsafe conditions. 

* * * * * 

■ 15. Amend § 25.929 by revising 

paragraph (a) to read as follows: 

§ 25.929 Propeller deicing. 

(a) If certification for flight in icing is 

sought there must be a means to prevent 

or remove hazardous ice accumulations 

that could form in the icing conditions 

defined in Appendix C of this part and 

in the portions of Appendix O of this 

part for which the airplane is approved 

for flight on propellers or on accessories 

where ice accumulation would 

jeopardize engine performance. 

* * * * * 

■ 16. Amend § 25.1093 by revising 

paragraph (b) to read as follows: 

§ 25.1093 Induction system icing 

protection. 

* * * * * 

(b) Turbine engines. Except as 

provided in paragraph (b)(3) of this 

section, each engine, with all icing 

protection systems operating, must: 

(1) Operate throughout its flight 

power range, including the minimum 

descent idling speeds, in the icing 

conditions defined in Appendices C and 

O of this part, and Appendix D of part 

33 of this chapter, and in falling and 

blowing snow within the limitations 

established for the airplane for such 

operation, without the accumulation of 

ice on the engine, inlet system 

components, or airframe components 

that would do any of the following: 

(i) Adversely affect installed engine 

operation or cause a sustained loss of 

power or thrust; or an unacceptable 

increase in gas path operating 


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temperature; or an airframe/engine 

incompatibility; or 

(ii) Result in unacceptable temporary 

power loss or engine damage; or 

(iii) Cause a stall, surge, or flameout 

or loss of engine controllability (for 

example, rollback). 

(2) Operate at ground idle speed for a 

minimum of 30 minutes on the ground 

in the following icing conditions shown 

in Table 1 of this section, unless 

replaced by similar test conditions that 

are more critical. These conditions must 

be demonstrated with the available air 

bleed for icing protection at its critical 

condition, without adverse effect, 

followed by an acceleration to takeoff 

power or thrust in accordance with the 

procedures defined in the airplane flight 

manual. During the idle operation, the 

engine may be run up periodically to a 

moderate power or thrust setting in a 

manner acceptable to the Administrator. 

Analysis may be used to show ambient 

temperatures below the tested 

temperature are less critical. The 

applicant must document the engine 

run-up procedure (including the 

maximum time interval between runups from idle, run-up power setting, and 

duration at power), the associated 

minimum ambient temperature, and the 

maximum time interval. These 

conditions must be used in the analysis 

that establishes the airplane operating 

limitations in accordance with 

§ 25.1521. 

(3) For the purposes of this section, 

the icing conditions defined in 

appendix O of this part, including the 

conditions specified in Condition 3 of 

Table 1 of this section, are not 

applicable to airplanes with a maximum 

takeoff weight equal to or greater than 

60,000 pounds. 

TABLE 1—ICING CONDITIONS FOR GROUND TESTS

Condition Total air temperature Water concentration 

(minimum) 

Mean effective particle 

diameter Demonstration 

1. Rime ice condition ..... 0 to 15 °F (18 to ¥9 °C) Liquid—0.3 g/m3 ............ 15–25 microns ............... By test, analysis or combination of 

the two. 

2. Glaze ice condition .... 20 to 30 °F (¥7 to ¥1 

°C).

Liquid—0.3 g/m3 ............ 15–25 microns ............... By test, analysis or combination of 

the two. 

3. Large drop condition 15 to 30 °F (¥9 to ¥1 

°C).

Liquid—0.3 g/m3 ............ 100 microns (minimum) By test, analysis or combination of 

the two. 

* * * * * 

■ 17. Amend § 25.1323 by revising 

paragraph (i) to read as follows: 

§ 25.1323 Airspeed indicating system. 

* * * * * 

(i) Each system must have a heated 

pitot tube or an equivalent means of 

preventing malfunction in the heavy 

rain conditions defined in Table 1 of 

this section; mixed phase and ice crystal 

conditions as defined in part 33, 

Appendix D, of this chapter; the icing 

conditions defined in Appendix C of 

this part; and the following icing 

conditions specified in Appendix O of 

this part: 

(1) For airplanes certificated in 

accordance with § 25.1420(a)(1), the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(2) For airplanes certificated in 

accordance with § 25.1420(a)(2), the 

icing conditions that the airplane is 

certified to safely operate in and the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(3) For airplanes certificated in 

accordance with § 25.1420(a)(3) and for 

airplanes not subject to § 25.1420, all 

icing conditions. 

TABLE 1—HEAVY RAIN CONDITIONS FOR AIRSPEED INDICATING SYSTEM TESTS

Altitude range Liquid water 

content 

Horizontal extent Droplet MVD 

(ft) (m) (g/m3) (km) (nmiles) (μm) 

0 to 10 000 ....................................... 0 to 3000 ......................................... 1 100 50 1000 

6 5 3 2000 

15 1 0 .5 2000 

* * * * * 

■ 18. Amend part 25 by adding a new 

section § 25.1324 to read as follows: 

§ 25.1324 Angle of attack system. 

Each angle of attack system sensor 

must be heated or have an equivalent 

means of preventing malfunction in the 

heavy rain conditions defined in Table 

1 of § 25.1323, the mixed phase and ice 

crystal conditions as defined in part 33, 

Appendix D, of this chapter, the icing 

conditions defined in Appendix C of 

this part, and the following icing 

conditions specified in Appendix O of 

this part: 

(a) For airplanes certificated in 

accordance with § 25.1420(a)(1), the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(b) For airplanes certificated in 

accordance with § 25.1420(a)(2), the 

icing conditions that the airplane is 

certified to safely operate in and the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(c) For airplanes certificated in 

accordance with § 25.1420(a)(3) and for 

airplanes not subject to § 25.1420, all 

icing conditions. 

■ 19. Amend § 25.1325 by revising 

paragraph (b) to read as follows: 

§ 25.1325 Static pressure systems. 

* * * * * 

(b) Each static port must be designed 

and located so that: 

(1) The static pressure system 

performance is least affected by airflow 

variation, or by moisture or other 

foreign matter; and 

(2) The correlation between air 

pressure in the static pressure system 

and true ambient atmospheric static 

pressure is not changed when the 

airplane is exposed to the icing 

conditions defined in Appendix C of 


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this part, and the following icing 

conditions specified in Appendix O of 

this part: 

(i) For airplanes certificated in 

accordance with § 25.1420(a)(1), the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(ii) For airplanes certificated in 

accordance with § 25.1420(a)(2), the 

icing conditions that the airplane is 

certified to safely operate in and the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(iii) For airplanes certificated in 

accordance with § 25.1420(a)(3) and for 

airplanes not subject to § 25.1420, all 

icing conditions. 

* * * * * 

■ 20. Amend part 25 by adding a new 

§ 25.1420 to read as follows: 

§ 25.1420 Supercooled large drop icing 

conditions. 

(a) If certification for flight in icing 

conditions is sought, in addition to the 

requirements of § 25.1419, an airplane 

with a maximum takeoff weight less 

than 60,000 pounds or with reversible 

flight controls must be capable of 

operating in accordance with 

paragraphs (a)(1), (2), or (3), of this 

section. 

(1) Operating safely after encountering 

the icing conditions defined in 

Appendix O of this part: 

(i) The airplane must have a means to 

detect that it is operating in Appendix 

O icing conditions; and 

(ii) Following detection of Appendix 

O icing conditions, the airplane must be 

capable of operating safely while exiting 

all icing conditions. 

(2) Operating safely in a portion of the 

icing conditions defined in Appendix O 

of this part as selected by the applicant: 

(i) The airplane must have a means to 

detect that it is operating in conditions 

that exceed the selected portion of 

Appendix O icing conditions; and 

(ii) Following detection, the airplane 

must be capable of operating safely 

while exiting all icing conditions. 

(3) Operating safely in the icing 

conditions defined in Appendix O of 

this part. 

(b) To establish that the airplane can 

operate safely as required in paragraph 

(a) of this section, an applicant must 

show through analysis that the ice 

protection for the various components 

of the airplane is adequate, taking into 

account the various airplane operational 

configurations. To verify the analysis, 

one, or more as found necessary, of the 

following methods must be used: 

(1) Laboratory dry air or simulated 

icing tests, or a combination of both, of 

the components or models of the 

components. 

(2) Laboratory dry air or simulated 

icing tests, or a combination of both, of 

models of the airplane. 

(3) Flight tests of the airplane or its 

components in simulated icing 

conditions, measured as necessary to 

support the analysis. 

(4) Flight tests of the airplane with 

simulated ice shapes. 

(5) Flight tests of the airplane in 

natural icing conditions, measured as 

necessary to support the analysis. 

(c) For an airplane certified in 

accordance with paragraph (a)(2) or (3) 

of this section, the requirements of 

§ 25.1419(e), (f), (g), and (h) must be met 

for the icing conditions defined in 

Appendix O of this part in which the 

airplane is certified to operate. 

(d) For the purposes of this section, 

the following definitions apply: 

(1) Reversible Flight Controls. Flight 

controls in the normal operating 

configuration that have force or motion 

originating at the airplane’s control 

surface (for example, through 

aerodynamic loads, static imbalance, or 

trim or servo tab inputs) that is 

transmitted back to flight deck controls. 

This term refers to flight deck controls 

connected to the pitch, roll, or yaw 

control surfaces by direct mechanical 

linkages, cables, or push-pull rods in 

such a way that pilot effort produces 

motion or force about the hinge line. 

(2) Simulated Icing Test. Testing 

conducted in simulated icing 

conditions, such as in an icing tunnel or 

behind an icing tanker. 

(3) Simulated Ice Shape. Ice shape 

fabricated from wood, epoxy, or other 

materials by any construction 

technique. 

■ 21. Amend § 25.1521 by redesignating 

paragraph (c)(3) as paragraph (c)(4), 

revising newly redesignated paragraph 

(c)(4), and adding new paragraph (c)(3) 

to read as follows: 

§ 25.1521 Powerplant limitations. 

* * * * * 

(c) * * * 

(3) Maximum time interval between 

engine run-ups from idle, run-up power 

setting and duration at power for ground 

operation in icing conditions, as defined 

in § 25.1093(b)(2). 

(4) Any other parameter for which a 

limitation has been established as part 

of the engine type certificate except that 

a limitation need not be established for 

a parameter that cannot be exceeded 

during normal operation due to the 

design of the installation or to another 

established limitation. 

* * * * * 

■ 22. Amend § 25.1533 by adding a new 

paragraph (c) to read as follows: 

§ 25.1533 Additional operating limitations. 

* * * * * 

(c) For airplanes certified in 

accordance with § 25.1420(a)(1) or (2), 

an operating limitation must be 

established to: 

(1) Prohibit intentional flight, 

including takeoff and landing, into icing 

conditions defined in Appendix O of 

this part for which the airplane has not 

been certified to safely operate; and 

(2) Require exiting all icing conditions 

if icing conditions defined in Appendix 

O of this part are encountered for which 

the airplane has not been certified to 

safely operate. 

■ 23. Amend Appendix C to part 25, in 

part II, by revising paragraph (a)(1), the 

second sentence of paragraph (a)(2), and 

paragraph (d)(2) to read as follows: 

Appendix C to Part 25 

* * * * * 

PART II—AIRFRAME ICE ACCRETIONS 

FOR SHOWING COMPLIANCE WITH 

SUBPART B 

(a) * * * 

(1) Takeoff ice is the most critical ice 

accretion on unprotected surfaces and any 

ice accretion on the protected surfaces 

appropriate to normal ice protection system 

operation, occurring between the end of the 

takeoff distance and 400 feet above the 

takeoff surface, assuming accretion starts at 

the end of the takeoff distance in the takeoff 

maximum icing conditions defined in part I 

of this Appendix. 

(2) * * * Ice accretion is assumed to start 

at the end of the takeoff distance in the 

takeoff maximum icing conditions of part I, 

paragraph (c) of this Appendix. 

* * * * * 

(d) * * * 

(2) The ice accretion starts at the end of the 

takeoff distance. 

* * * * * 

■ 24. Amend part 25 by adding new 

Appendix O to read as follows: 

Appendix O to Part 25—Supercooled 

Large Drop Icing Conditions 

This Appendix consists of two parts. Part 

I defines this Appendix as a description of 

supercooled large drop icing conditions in 

which the drop median volume diameter 

(MVD) is less than or greater than 40 mm, the 

maximum mean effective drop diameter 

(MED) of Appendix C of this part continuous 

maximum (stratiform clouds) icing 

conditions. For this Appendix, supercooled 

large drop icing conditions consist of freezing 

drizzle and freezing rain occurring in and/or 

below stratiform clouds. Part II defines ice 

accretions used to show compliance with the 

airplane performance and handling qualities 

requirements of subpart B of this part. 


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PART I—METEOROLOGY 

In this Appendix icing conditions are 

defined by the parameters of altitude, vertical 

and horizontal extent, temperature, liquid 

water content, and water mass distribution as 

a function of drop diameter distribution. 

(a) Freezing Drizzle (Conditions with 

spectra maximum drop diameters from 

100mm to 500 mm): 

(1) Pressure altitude range: 0 to 22,000 feet 

MSL. 

(2) Maximum vertical extent: 12,000 feet. 

(3) Horizontal extent: Standard distance of 

17.4 nautical miles. 

(4) Total liquid water content. 

Note: Liquid water content (LWC) in grams 

per cubic meter (g/m3) based on horizontal 

extent standard distance of 17.4 nautical 

miles. 

(5) Drop diameter distribution: Figure 2. 

(6) Altitude and temperature envelope: 

Figure 3. 

(b) Freezing Rain (Conditions with spectra 

maximum drop diameters greater than 500 

mm): 

(1) Pressure altitude range: 0 to 12,000 ft 

MSL. 

(2) Maximum vertical extent: 7,000 ft. 

(3) Horizontal extent: Standard distance of 

17.4 nautical miles. 

(4) Total liquid water content. 

Note: LWC in grams per cubic meter (g/m3) 

based on horizontal extent standard distance 

of 17.4 nautical miles. 

(5) Drop Diameter Distribution: Figure 5. 

(6) Altitude and temperature envelope: 

Figure 6. 

(c) Horizontal extent. 

The liquid water content for freezing 

drizzle and freezing rain conditions for 

horizontal extents other than the standard 

17.4 nautical miles can be determined by the 

value of the liquid water content determined 

from Figure 1 or Figure 4, multiplied by the 

factor provided in Figure 7, which is defined 

by the following equation: 

S = 1.266 ¥ 0.213 log10(H) 

Where: 

S = Liquid Water Content Scale Factor 

(dimensionless) and 

H = horizontal extent in nautical miles 

BILLING CODE 4910–13–P 


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65530 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 


tkelley on DSK3SPTVN1PROD with RULES2ER04NO14.002</GPH>

FIGURE 2-Appendix 0, Freezing Drizzle, Drop Diameter Distribution 

1 

en 

~ 0.8 

2 

Q,) 0.6 . ;;::: 

l20.4 -::I 

E 

::I 0.2 

0 

0 

101 

1 

en 

~ 0.8 

2 

Q,) 0.6 . ;;::: 

l20.4 -

::I 

E 

::I 0.2 

0 

0 

101 

.. · .... ! ... , ........................... . .. 

............. .- .. • .................. : ..........•• !.•I•I•!···· 

.. i !Freezing Drizzle MVD H 40 micron 

102 103 

Diameter (microns) 

: : I· . : ... · ... : ... 

: : ~ ~ 

. ITII . • .• !Freezing Drizzle MVD :>, 40 micron 

102 103 

Diameter (microns) 
Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 65531 


tkelley on DSK3SPTVN1PROD with RULES2ER04NO14.003</GPH> ER04NO14.004</GPH>

FIGURE 3 -Appendix 0, Freezing Drizzle, Temperature and Altitude 

-30~------~--------~------~--------~------~ 

0 5 10 15 20 25 

Pressure Altitude (1 000-feet) 

FIGURE 4-Appendix 0, Freezing Rain, Liquid Water Content 

.... 

Q) 

:-2 ~ 0.1 

::::l 

C" 

:.J 

-25 -20 -15 -10 -5 0 5 

Ambient Temperature (degrees Celsius) 
65532 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 


tkelley on DSK3SPTVN1PROD with RULES2ER04NO14.005</GPH>

en 

~ 0.8 

::;?! 

Q) 0.6 

.::::: 

-cao.4 

::I 

E 

::I 0.2 

(.) 

en 

~ 0.8 

::;?! 

Q) 0.6 

.::::: 

-cao.4 

::I 

E 

::I 0.2 

(.) 

FIGURE 5-Appendix 0, Freezing Rain, Drop Diameter Distribution 

: : ~ . . . . 

· !Fr~~~irig Rain MVD ; 4p microns o~~~--~~~~~~----~~~~~LL--~~ 

101 102 103 

Diameter (microns) 
Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 65533 


tkelley on DSK3SPTVN1PROD with RULES2ER04NO14.006</GPH>

FIGURE 6 -Appendix 0, Freezing Rain, Temperature and Altitude 

5 

~ 0 

"iii 

Q) 

u 

en -5 

Q) 

~ C) 

,_... 

~ -10 

~ ~ 

li! -15 

Q) 

c.. 

E 

~-20 

"'E 

Q) 

:..c E -25 

<( 

5 10 15 20 25 

Pressure Altitude (1 000-feet) 
65534 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 

BILLING CODE 4910–13–C 

PART II—AIRFRAME ICE ACCRETIONS 

FOR SHOWING COMPLIANCE WITH 

SUBPART B OF THIS PART 

(a) General. 

The most critical ice accretion in terms of 

airplane performance and handling qualities 

for each flight phase must be used to show 

compliance with the applicable airplane 

performance and handling qualities 

requirements for icing conditions contained 

in subpart B of this part. Applicants must 

demonstrate that the full range of 

atmospheric icing conditions specified in 

part I of this Appendix have been considered, 

including drop diameter distributions, liquid 

water content, and temperature appropriate 

to the flight conditions (for example, 

configuration, speed, angle of attack, and 

altitude). 

(1) For an airplane certified in accordance 

with § 25.1420(a)(1), the ice accretions for 

each flight phase are defined in part II, 

paragraph (b) of this Appendix. 

(2) For an airplane certified in accordance 

with § 25.1420(a)(2), the most critical ice 

accretion for each flight phase defined in part 

II, paragraphs (b) and (c) of this Appendix, 

must be used. For the ice accretions defined 

in part II, paragraph (c) of this Appendix, 

only the portion of part I of this Appendix 

in which the airplane is capable of operating 

safely must be considered. 

(3) For an airplane certified in accordance 

with § 25.1420(a)(3), the ice accretions for 

each flight phase are defined in part II, 

paragraph (c) of this Appendix. 

(b) Ice accretions for airplanes certified in 

accordance with § 25.1420(a)(1) or (2). 

(1) En route ice is the en route ice as 

defined by part II, paragraph (c)(3), of this 

Appendix, for an airplane certified in 

accordance with § 25.1420(a)(2), or defined 

by part II, paragraph (a)(3), of Appendix C of 

this part, for an airplane certified in 

accordance with § 25.1420(a)(1), plus: 

(i) Pre-detection ice as defined by part II, 

paragraph (b)(5), of this Appendix; and 

(ii) The ice accumulated during the transit 

of one cloud with a horizontal extent of 17.4 

nautical miles in the most critical of the icing 

conditions defined in part I of this Appendix 

and one cloud with a horizontal extent of 

17.4 nautical miles in the continuous 

maximum icing conditions defined in 

Appendix C of this part. 

(2) Holding ice is the holding ice defined 

by part II, paragraph (c)(4), of this Appendix, 

for an airplane certified in accordance with 

§ 25.1420(a)(2), or defined by part II, 

paragraph (a)(4), of Appendix C of this part, 

for an airplane certified in accordance with 

§ 25.1420(a)(1), plus: 

(i) Pre-detection ice as defined by part II, 

paragraph (b)(5), of this Appendix; and 

(ii) The ice accumulated during the transit 

of one cloud with a 17.4 nautical miles 

horizontal extent in the most critical of the 

icing conditions defined in part I of this 

Appendix and one cloud with a horizontal 

extent of 17.4 nautical miles in the 

continuous maximum icing conditions 

defined in Appendix C of this part. 

(iii) Except the total exposure to holding 

ice conditions does not need to exceed 45 

minutes. 

(3) Approach ice is the more critical of the 

holding ice defined by part II, paragraph 

(b)(2), of this Appendix, or the ice calculated 

in the applicable paragraphs (b)(3)(i) or (ii) of 

part II, of this Appendix: 

(i) For an airplane certified in accordance 

with § 25.1420(a)(2), the ice accumulated 

during descent from the maximum vertical 

extent of the icing conditions defined in part 

I of this Appendix to 2,000 feet above the 

landing surface in the cruise configuration, 

plus transition to the approach configuration, 

plus: 

(A) Pre-detection ice, as defined by part II, 

paragraph (b)(5), of this Appendix; and 

(B) The ice accumulated during the transit 

at 2,000 feet above the landing surface of one 

cloud with a horizontal extent of 17.4 

nautical miles in the most critical of the icing 

conditions defined in part I of this Appendix 

and one cloud with a horizontal extent of 

17.4 nautical miles in the continuous 

maximum icing conditions defined in 

Appendix C of this part. 


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Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 65535 

(ii) For an airplane certified in accordance 

with § 25.1420(a)(1), the ice accumulated 

during descent from the maximum vertical 

extent of the maximum continuous icing 

conditions defined in part I of Appendix C 

to 2,000 feet above the landing surface in the 

cruise configuration, plus transition to the 

approach configuration, plus: 

(A) Pre-detection ice, as defined by part II, 

paragraph (b)(5), of this Appendix; and 

(B) The ice accumulated during the transit 

at 2,000 feet above the landing surface of one 

cloud with a horizontal extent of 17.4 

nautical miles in the most critical of the icing 

conditions defined in part I of this Appendix 

and one cloud with a horizontal extent of 

17.4 nautical miles in the continuous 

maximum icing conditions defined in 

Appendix C of this part. 

(4) Landing ice is the more critical of the 

holding ice as defined by part II, paragraph 

(b)(2), of this Appendix, or the ice calculated 

in the applicable paragraphs (b)(4)(i) or (ii) of 

part II of this Appendix: 

(i) For an airplane certified in accordance 

with § 25.1420(a)(2), the ice accretion defined 

by part II, paragraph (c)(5)(i), of this 

Appendix, plus a descent from 2,000 feet 

above the landing surface to a height of 200 

feet above the landing surface with a 

transition to the landing configuration in the 

icing conditions defined in part I of this 

Appendix, plus: 

(A) Pre-detection ice, as defined in part II, 

paragraph (b)(5), of this Appendix; and 

(B) The ice accumulated during an exit 

maneuver, beginning with the minimum 

climb gradient required by § 25.119, from a 

height of 200 feet above the landing surface 

through one cloud with a horizontal extent 

of 17.4 nautical miles in the most critical of 

the icing conditions defined in part I of this 

Appendix and one cloud with a horizontal 

extent of 17.4 nautical miles in the 

continuous maximum icing conditions 

defined in Appendix C of this part. 

(ii) For an airplane certified in accordance 

with § 25.1420(a)(1), the ice accumulated in 

the maximum continuous icing conditions 

defined in Appendix C of this part, during a 

descent from the maximum vertical extent of 

the icing conditions defined in Appendix C 

of this part, to 2,000 feet above the landing 

surface in the cruise configuration, plus 

transition to the approach configuration and 

flying for 15 minutes at 2,000 feet above the 

landing surface, plus a descent from 2,000 

feet above the landing surface to a height of 

200 feet above the landing surface with a 

transition to the landing configuration, plus: 

(A) Pre-detection ice, as described by part 

II, paragraph (b)(5), of this Appendix; and 

(B) The ice accumulated during an exit 

maneuver, beginning with the minimum 

climb gradient required by § 25.119, from a 

height of 200 feet above the landing surface 

through one cloud with a horizontal extent 

of 17.4 nautical miles in the most critical of 

the icing conditions defined in part I of this 

Appendix and one cloud with a horizontal 

extent of 17.4 nautical miles in the 

continuous maximum icing conditions 

defined in Appendix C of this part. 

(5) Pre-detection ice is the ice accretion 

before detection of flight conditions in this 

Appendix that require exiting per 

§ 25.1420(a)(1) and (2). It is the pre-existing 

ice accretion that may exist from operating in 

icing conditions in which the airplane is 

approved to operate prior to encountering the 

icing conditions requiring an exit, plus the 

ice accumulated during the time needed to 

detect the icing conditions, followed by two 

minutes of further ice accumulation to take 

into account the time for the flightcrew to 

take action to exit the icing conditions, 

including coordination with air traffic 

control. 

(i) For an airplane certified in accordance 

with § 25.1420(a)(1), the pre-existing ice 

accretion must be based on the icing 

conditions defined in Appendix C of this 

part. 

(ii) For an airplane certified in accordance 

with § 25.1420(a)(2), the pre-existing ice 

accretion must be based on the more critical 

of the icing conditions defined in Appendix 

C of this part, or the icing conditions defined 

in part I of this Appendix in which the 

airplane is capable of safely operating. 

(c) Ice accretions for airplanes certified in 

accordance with §§ 25.1420(a)(2) or (3). For 

an airplane certified in accordance with 

§ 25.1420(a)(2), only the portion of the icing 

conditions of part I of this Appendix in 

which the airplane is capable of operating 

safely must be considered. 

(1) Takeoff ice is the most critical ice 

accretion on unprotected surfaces, and any 

ice accretion on the protected surfaces, 

occurring between the end of the takeoff 

distance and 400 feet above the takeoff 

surface, assuming accretion starts at the end 

of the takeoff distance in the icing conditions 

defined in part I of this Appendix. 

(2) Final takeoff ice is the most critical ice 

accretion on unprotected surfaces, and any 

ice accretion on the protected surfaces 

appropriate to normal ice protection system 

operation, between 400 feet and either 1,500 

feet above the takeoff surface, or the height 

at which the transition from the takeoff to the 

en route configuration is completed and VFTO

is reached, whichever is higher. Ice accretion 

is assumed to start at the end of the takeoff 

distance in the icing conditions defined in 

part I of this Appendix. 

(3) En route ice is the most critical ice 

accretion on the unprotected surfaces, and 

any ice accretion on the protected surfaces 

appropriate to normal ice protection system 

operation, during the en route flight phase in 

the icing conditions defined in part I of this 

Appendix. 

(4) Holding ice is the most critical ice 

accretion on the unprotected surfaces, and 

any ice accretion on the protected surfaces 

appropriate to normal ice protection system 

operation, resulting from 45 minutes of flight 

within a cloud with a 17.4 nautical miles 

horizontal extent in the icing conditions 

defined in part I of this Appendix, during the 

holding phase of flight. 

(5) Approach ice is the ice accretion on the 

unprotected surfaces, and any ice accretion 

on the protected surfaces appropriate to 

normal ice protection system operation, 

resulting from the more critical of the: 

(i) Ice accumulated in the icing conditions 

defined in part I of this Appendix during a 

descent from the maximum vertical extent of 

the icing conditions defined in part I of this 

Appendix, to 2,000 feet above the landing 

surface in the cruise configuration, plus 

transition to the approach configuration and 

flying for 15 minutes at 2,000 feet above the 

landing surface; or 

(ii) Holding ice as defined by part II, 

paragraph (c)(4), of this Appendix. 

(6) Landing ice is the ice accretion on the 

unprotected surfaces, and any ice accretion 

on the protected surfaces appropriate to 

normal ice protection system operation, 

resulting from the more critical of the: 

(i) Ice accretion defined by part II, 

paragraph (c)(5)(i), of this Appendix, plus ice 

accumulated in the icing conditions defined 

in part I of this Appendix during a descent 

from 2,000 feet above the landing surface to 

a height of 200 feet above the landing surface 

with a transition to the landing configuration, 

followed by a go-around at the minimum 

climb gradient required by § 25.119, from a 

height of 200 feet above the landing surface 

to 2,000 feet above the landing surface, flying 

for 15 minutes at 2,000 feet above the landing 

surface in the approach configuration, and a 

descent to the landing surface (touchdown) 

in the landing configuration; or 

(ii) Holding ice as defined by part II, 

paragraph (c)(4), of this Appendix. 

(7) For both unprotected and protected 

parts, the ice accretion for the takeoff phase 

must be determined for the icing conditions 

defined in part I of this Appendix, using the 

following assumptions: 

(i) The airfoils, control surfaces, and, if 

applicable, propellers are free from frost, 

snow, or ice at the start of takeoff; 

(ii) The ice accretion starts at the end of the 

takeoff distance; 

(iii) The critical ratio of thrust/power-toweight; 

(iv) Failure of the critical engine occurs at 

VEF; and 

(v) Crew activation of the ice protection 

system is in accordance with a normal 

operating procedure provided in the airplane 

flight manual, except that after beginning the 

takeoff roll, it must be assumed that the crew 

takes no action to activate the ice protection 

system until the airplane is at least 400 feet 

above the takeoff surface. 

(d) The ice accretion before the ice 

protection system has been activated and is 

performing its intended function is the 

critical ice accretion formed on the 

unprotected and normally protected surfaces 

before activation and effective operation of 

the ice protection system in the icing 

conditions defined in part I of this Appendix. 

This ice accretion only applies in showing 

compliance to §§ 25.143(j) and 25.207(h). 

(e) In order to reduce the number of ice 

accretions to be considered when 

demonstrating compliance with the 

requirements of § 25.21(g), any of the ice 

accretions defined in this Appendix may be 

used for any other flight phase if it is shown 

to be at least as critical as the specific ice 

accretion defined for that flight phase. 

Configuration differences and their effects on 

ice accretions must be taken into account. 

(f) The ice accretion that has the most 

adverse effect on handling qualities may be 

used for airplane performance tests provided 

any difference in performance is 

conservatively taken into account. 


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65536 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 

PART 33—AIRWORTHINESS 

STANDARDS: AIRCRAFT ENGINES 

■ 25. The authority citation for part 33 

is revised to read as follows: 

Authority: 49 U.S.C. 106(g), 40113, 44701, 

44702, 44704. 

■ 26. Revise § 33.68 to read as follows: 

§ 33.68 Induction system icing. 

Each engine, with all icing protection 

systems operating, must: 

(a) Operate throughout its flight 

power range, including the minimum 

descent idle rotor speeds achievable in 

flight, in the icing conditions defined 

for turbojet, turbofan, and turboprop 

engines in Appendices C and O of part 

25 of this chapter, and Appendix D of 

this part, and for turboshaft engines in 

Appendix C of part 29 of this chapter, 

without the accumulation of ice on the 

engine components that: 

(1) Adversely affects engine operation 

or that causes an unacceptable 

permanent loss of power or thrust or 

unacceptable increase in engine 

operating temperature; or 

(2) Results in unacceptable temporary 

power loss or engine damage; or 

(3) Causes a stall, surge, or flameout 

or loss of engine controllability. The 

applicant must account for in-flight ram 

effects in any critical point analysis or 

test demonstration of these flight 

conditions. 

(b) Operate throughout its flight 

power range, including minimum 

descent idle rotor speeds achievable in 

flight, in the icing conditions defined 

for turbojet, turbofan, and turboprop 

engines in Appendices C and O of part 

25 of this chapter, and for turboshaft 

engines in Appendix C of part 29 of this 

chapter. In addition: 

(1) It must be shown through Critical 

Point Analysis (CPA) that the complete 

ice envelope has been analyzed, and 

that the most critical points must be 

demonstrated by engine test, analysis, or 

a combination of the two to operate 

acceptably. Extended flight in critical 

flight conditions such as hold, descent, 

approach, climb, and cruise, must be 

addressed, for the ice conditions 

defined in these appendices. 

(2) It must be shown by engine test, 

analysis, or a combination of the two 

that the engine can operate acceptably 

for the following durations: 

(i) At engine powers that can sustain 

level flight: A duration that achieves 

repetitive, stabilized operation for 

turbojet, turbofan, and turboprop 

engines in the icing conditions defined 

in Appendices C and O of part 25 of this 

chapter, and for turboshaft engines in 

the icing conditions defined in 

Appendix C of part 29 of this chapter. 

(ii) At engine power below that which 

can sustain level flight: 

(A) Demonstration in altitude flight 

simulation test facility: A duration of 10 

minutes consistent with a simulated 

flight descent of 10,000 ft (3 km) in 

altitude while operating in Continuous 

Maximum icing conditions defined in 

Appendix C of part 25 of this chapter for 

turbojet, turbofan, and turboprop 

engines, and for turboshaft engines in 

the icing conditions defined in 

Appendix C of part 29 of this chapter, 

plus 40 percent liquid water content 

margin, at the critical level of airspeed 

and air temperature; or 

(B) Demonstration in ground test 

facility: A duration of 3 cycles of 

alternating icing exposure 

corresponding to the liquid water 

content levels and standard cloud 

lengths starting in Intermittent 

Maximum and then in Continuous 

Maximum icing conditions defined in 

Appendix C of part 25 of this chapter for 

turbojet, turbofan, and turboprop 

engines, and for turboshaft engines in 

the icing conditions defined in 

Appendix C of part 29 of this chapter, 

at the critical level of air temperature. 

(c) In addition to complying with 

paragraph (b) of this section, the 

following conditions shown in Table 1 

of this section unless replaced by 

similar CPA test conditions that are 

more critical or produce an equivalent 

level of severity, must be demonstrated 

by an engine test: 

TABLE 1—CONDITIONS THAT MUST BE DEMONSTRATED BY AN ENGINE TEST

Condition Total air temperature 

Supercooled water 

concentrations 

(minimum) 

Median volume drop 

diameter Duration 

1. Glaze ice conditions ........ 21 to 25 °F (-6 to -4 °C) ..... 2 g/m3 ................................. 25 to 35 microns ....... (a) 10-minutes for power 

below sustainable level 

flight (idle descent). 

(b) Must show repetitive, 

stabilized operation for 

higher powers (50%, 

75%, 100%MC). 

2. Rime ice conditions ......... -10 to 0 °F (-23 to -18 °C) .. 1 g/m3 ................................. 15 to 25 microns ....... (a) 10-minutes for power 

below sustainable level 

flight (idle descent). 

(b) Must show repetitive, 

stabilized operation for 

higher powers (50%, 

75%, 100%MC). 

3. Glaze ice holding conditions.

(Turbojet, turbofan, and turboprop only).

Turbojet and Turbofan, 

only: 10 to 18 °F (-12 to 

-8 °C).

Alternating cycle: First 1.7 

g/m3 (1 minute), Then 0.3 

g/m3 (6 minute).

20 to 30 microns ....... Must show repetitive, stabilized operation (or 45 

minutes max). 

Turboprop, only: 2 to 10 °F 

(-17 to -12 °C).

............................................. ....................................

4. Rime ice holding conditions.

(Turbojet, turbofan, and turboprop only).

Turbojet and Turbofan, 

only: -10 to 0 °F (-23 to 

-18 °C).

0.25 g/m3 ............................ 20 to 30 microns ....... Must show repetitive, stabilized operation (or 45 

minutes max). 

Turboprop, only: 2 to 10 °F 

(-17 to -12 °C).

............................................. ....................................


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Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 65537 

(d) Operate at ground idle speed for 

a minimum of 30 minutes at each of the 

following icing conditions shown in 

Table 2 of this section with the available 

air bleed for icing protection at its 

critical condition, without adverse 

effect, followed by acceleration to 

takeoff power or thrust. During the idle 

operation, the engine may be run up 

periodically to a moderate power or 

thrust setting in a manner acceptable to 

the Administrator. Analysis may be 

used to show ambient temperatures 

below the tested temperature are less 

critical. The applicant must document 

any demonstrated run ups and 

minimum ambient temperature 

capability in the engine operating 

manual as mandatory in icing 

conditions. The applicant must 

demonstrate, with consideration of 

expected airport elevations, the 

following: 

TABLE 2—DEMONSTRATION METHODS FOR SPECIFIC ICING CONDITIONS

Condition Total air temperature 

Supercooled water concentrations 

(minimum) 

Mean effective particle diameter Demonstration 

1. Rime ice condition ........... 0 to 15 °F (-18 to -9 °C) ..... Liquid—0.3 g/m3 ................. 15–25 microns ........... By engine test. 

2. Glaze ice condition .......... 20 to 30 °F (-7 to -1 °C) ..... Liquid—0.3 g/m3 ................. 15–25 microns ........... By engine test. 

3. Snow ice condition .......... 26 to 32 °F (-3 to 0 °C) ...... Ice—0.9 g/m3 ...................... 100 microns ...............

(minimum) ..................

By test, analysis or combination of the two. 

4. Large drop glaze ice condition (Turbojet, turbofan, 

and turboprop only).

15 to 30 °F (-9 to -1 °C) ..... Liquid—0.3 g/m3 ................. 100 microns (minimum).By test, analysis or combination of the two. 

(e) Demonstrate by test, analysis, or 

combination of the two, acceptable 

operation for turbojet, turbofan, and 

turboprop engines in mixed phase and 

ice crystal icing conditions throughout 

Appendix D of this part, icing envelope 

throughout its flight power range, 

including minimum descent idling 

speeds. 

■ 27. Amend § 33.77 by adding 

paragraph (a) and revising paragraphs 

(c) introductory text, (c)(1), (d), and (e) 

to read as follows: 

§ 33.77 Foreign object ingestion ice. 

(a) Compliance with the requirements 

of this section must be demonstrated by 

engine ice ingestion test or by validated 

analysis showing equivalence of other 

means for demonstrating soft body 

damage tolerance. 

* * * * * 

(c) Ingestion of ice under the 

conditions of this section may not— 

(1) Cause an immediate or ultimate 

unacceptable sustained power or thrust 

loss; or 

* * * * * 

(d) For an engine that incorporates a 

protection device, compliance with this 

section need not be demonstrated with 

respect to ice formed forward of the 

protection device if it is shown that— 

(1) Such ice is of a size that will not 

pass through the protective device; 

(2) The protective device will 

withstand the impact of the ice; and 

(3) The ice stopped by the protective 

device will not obstruct the flow of 

induction air into the engine with a 

resultant sustained reduction in power 

or thrust greater than those values 

defined by paragraph (c) of this section. 

(e) Compliance with the requirements 

of this section must be demonstrated by 

engine ice ingestion test under the 

following ingestion conditions or by 

validated analysis showing equivalence 

of other means for demonstrating soft 

body damage tolerance. 

(1) The minimum ice quantity and 

dimensions will be established by the 

engine size as defined in Table 1 of this 

section. 

(2) The ingested ice dimensions are 

determined by linear interpolation 

between table values, and are based on 

the actual engine’s inlet hilite area. 

(3) The ingestion velocity will 

simulate ice from the inlet being sucked 

into the engine. 

(4) Engine operation will be at the 

maximum cruise power or thrust unless 

lower power is more critical. 

TABLE 1—MINIMUM ICE SLAB DIMENSIONS BASED ON ENGINE INLET SIZE

Engine Inlet Hilite area 

(sq. inch) 

Thickness 

(inch) 

Width 

(inch) 

Length 

(inch) 

0 ................................................................................................................................................. 0 .25 0 3.6 

80 ............................................................................................................................................... 0 .25 6 3.6 

300 ............................................................................................................................................. 0 .25 12 3.6 

700 ............................................................................................................................................. 0 .25 12 4.8 

2800 ........................................................................................................................................... 0 .35 12 8.5 

5000 ........................................................................................................................................... 0 .43 12 11.0 

7000 ........................................................................................................................................... 0 .50 12 12.7 

7900 ........................................................................................................................................... 0 .50 12 13.4 

9500 ........................................................................................................................................... 0 .50 12 14.6 

11300 ......................................................................................................................................... 0 .50 12 15.9 

13300 ......................................................................................................................................... 0 .50 12 17.1 

16500 ......................................................................................................................................... 0 .5 12 18.9 

20000 ......................................................................................................................................... 0 .5 12 20.0 


tkelley on DSK3SPTVN1PROD with RULES2
65538 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 

Appendix C [Added and Reserved] 

■ 28. Amend part 33 by adding and 

reserving a new Appendix C. 

■ 29. Amend part 33 by adding a new 

Appendix D to read as follows: 

Appendix D to Part 33—Mixed Phase 

and Ice Crystal Icing Envelope (Deep 

Convective Clouds) 

The ice crystal icing envelope is depicted 

in Figure D1 of this Appendix. 

BILLING CODE 4910–13–P 

Within the envelope, total water content 

(TWC) in g/m3 has been determined based 

upon the adiabatic lapse defined by the 

convective rise of 90% relative humidity air 

from sea level to higher altitudes and scaled 

by a factor of 0.65 to a standard cloud length 

of 17.4 nautical miles. Figure D2 of this 

Appendix displays TWC for this distance 

over a range of ambient temperature within 

the boundaries of the ice crystal envelope 

specified in Figure D1 of this Appendix. 


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Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 65539 

Ice crystal size median mass dimension 

(MMD) range is 50–200 microns (equivalent 

spherical size) based upon measurements 

near convective storm cores. 

The TWC can be treated as completely 

glaciated (ice crystal) except as noted in the 

Table 1 of this Appendix. 

TABLE 1—SUPERCOOLED LIQUID

PORTION OF TWC 

Temperature 

range—deg C 

Horizontal cloud 

length—nautical 

miles 

LWC— 

g/m3

0 to –20 ........... ≤50 .................. ≤1.0 

0 to –20 ........... Indefinite .......... ≤0.5 

< –20 ............... .......................... 0 

The TWC levels displayed in Figure D2 of 

this Appendix represent TWC values for a 

standard exposure distance (horizontal cloud 

length) of 17.4 nautical miles that must be 

adjusted with length of icing exposure. 


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65540 Federal Register / Vol. 79, No. 213 / Tuesday, November 4, 2014 / Rules and Regulations 

Issued under authority provided by 49 

U.S.C. 106(f) and 44701(a) in Washington, 

DC, on October 22, 2014. 

Michael P. Huerta, 

Administrator. 

[FR Doc. 2014–25789 Filed 11–3–14; 8:45 am] 

BILLING CODE 4910–13–C 


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