Federal Aviation Administration Aviation Rulemaking Advisory Committee Transport Airplane and Engine Issue Area Loads and Dynamics Harmonization Working Group Task 17 – Harmonize 14 CFR Part 25.415

## Task Assignment[Federal Register: November 26, 1999 (Volume 64, Number 227)] [Notices] [Page 66522-66524] From the Federal Register Online via GPO Access [wais.access.gpo.gov] [DOCID:fr26no99-123]

=======================================================================
----------------------------------------------------------------------- DEPARTMENT OF TRANSPORTATION Federal Aviation Administration
Aviation Rulemaking Advisory Committee; Transport Airplane and Engine Issues--New and Revised Tasks AGENCY: Federal Aviation Administration ( FAA), DOT. ACTION: Notice of new and revised task assignments for the Aviation Rulemaking Advisory Committee (ARAC).

----------------------------------------------------------------------- SUMMARY: Notice is given of new tasks assigned to and accepted by the Aviation Rulemaking Advisory Committee (ARAC) and of revisions to a number of existing tasks. This notice informs the public of the activities of ARAC. FOR FURTHER INFORMATION CONTACT: Dorenda Baker, Transport Airplane Directorate, Aircraft Certification Service (ANM-110), 1601 Lind Avenue, SW., Renton, WA 98055; phone (425) 227-2109; fax (425) 227- 1320.
SUPPLEMENTARY INFORMATION: Background The FAA has established an Aviation Rulemaking Advisory Committee to provide advice and recommendations to the FAA Administrator, through the Associate Administrator for Regulation and Certification, on the full range of the FAA 's rulemaking activities with respect to aviationrelated issues. This includes obtaining advice and recommendations on the FAA 's commitment to harmonize its Federal Aviation Regulations (FAR) and practices with its trading partners in Europe and Canada. One area ARAC deals with is transport airplane and engine issues. These issues involve the airworthiness standards for transport category [[Page 66523]] airplanes and engines in 14 CFR parts 25, 33, and 35 and parallel provisions in 14 CFR parts 121 and 135. The corresponding Canadian standards are contained in Parts V, VI, and VII of the Canadian Aviation Regulations. The corresponding European standards arecontained in Joint Aviation Requirements (JAR) 25, JAR-E, JAR-P, JAROPS-Part 1, and JAR-26. As proposed by the U.S. and European aviation industry, and asagreed between the Federal Aviation Administration ( FAA) and the European Joint Aviation Authorities (JAA), an accelerated process to reach harmonization has been adopted. This process is based on two procedures: (1) Accepting the more stringent of the regulations in Title 14 of the Code of Federal Regulations (FAR), Part 25, and the Joint Airworthiness Requirements (JAR); and (2) Assigning approximately 41 already-tasked significant regulatory differences (SRD), and certain additional part 25 regulatory differences, to one of three categories: <bullet> Category 1--Envelope <bullet> Category 2--Completed or near complete <bullet> Category 3--Harmonize The Revised Tasks ARAC will review the rules identified in the ``FAR/JAR 25 Differences List,'' dated June 30, 1999, and identify changes to the regulations necessary to harmonize part 25 and JAR 25. ARAC will submit a technical report on each rule. Each report will include the cost information that has been requested by the FAA. The tasks currently underway in ARAC to harmonize the listed rules are superseded by this tasking. New Tasks The FAA has submitted a number of new tasks for the Aviation Rulemaking Advisory Committee (ARAC), Transport Airplane and Engine Issues. As agreed by ARAC, these tasks will be accomplished by existing harmonization working groups. The tasks are regulatory differencesidentified in the above-referenced differences list as Rule type = PSRD. New Working Group In addition to the above new tasks, a newly established Cabin Safety Harmonization Working Group will review several FAR/JAR paragraphs as follows: ARAC will review the following rules and identify changes to the regulations necessary to harmonize part 25 and JAR: (1) Section 25.787; (2) Section 25.791(a) to (d); (3) Section 25.810; (4) Section 25.811; (5) Section 25.819; and (6) Section 25.813(c). ARAC will submit a technical report on each rule. Each report will include the cost information that has been requested by the FAA. The Cabin Safety Harmonization Working Group would be expected to complete its work for the first five items (identified as Category 1 or 2) before completing item 6 (identified as Category 3). ScheduleWithin 120 days of tasking/retasking: <bullet> For Category 1 tasks, ARAC submits the Working Groups' technical reports to the FAA to initiate drafting of proposed rulemaking documents. <bullet> For Category 2 tasks, ARAC submits technical reports, including already developed draft rules and/or advisory materials, to the FAA to complete legal review, economic analysis, coordination, and issuance. June 2000: For Category 3 tasks, ARAC submits technical reports including draft rules and/or advisory materials to the FAA to complete legal review, economic analysis, coordination, and issuance. ARAC Acceptance of Tasks ARAC has accepted the new tasks and has chosen to assign all but one of them to existing harmonization working groups. A new Cabin Safety Harmonization Working Group will be formed to complete the remaining tasks. The working groups serve as staff to ARAC to assist ARAC in the analysis of the assigned tasks. Working group recommendations must be reviewed and approved by ARAC. If ARAC accepts a working group's recommendations, it forwards them to the FAA and ARAC recommendations. Working Group Activity All working groups are expected to comply with the procedures adopted by ARAC. As part of the procedures, the working groups are expected to accomplish the following: 1. Document their decisions and discuss areas of disagreement, including options, in a report. A report can be used both for the enveloping and for the harmonization processes. 2. If requested by the FAA, provide support for disposition of the comments received in response to the NPRM or review the FAA 's prepared disposition of comments. If support is requested, the Working Group will review comments/disposition and prepare a report documenting their recommendations, agreement, or disagreement. This report will be submitted by ARAC back to the FAA. 3. Provide a status report at each meeting of ARAC held to consider Transport Airplane and Engine Issues. Partcipation in the Working Groups Membership on existing working groups will remain the same, with the formation of subtask groups, if appropriate. The Cabin Safety Harmonization Working Group will be composed of technical experts having an interest in the assigned task. A working group member need not be a representative of a member of the full committee. An individual who has expertise in the subject matter and wishes to become a member of the Cabin Safety Harmonization Working Group should write to the person listed under the caption FOR FURTHER INFORMATION CONTACT expressing that desire, describing his or her interest in the tasks, and stating the expertise he or she would bring to the working group. All requests to participate must be received no later than December 30, 1999. The requests will be reviewed by the assistant chair, the assistant executive director, and the working group chair, and the individuals will be advised whether or not the request can be accommodated.Individuals chosen for membership on the Cabin Safety Harmonization Working Group will be expected to represent their aviation community segment and participate actively in the working group (e.g., attend all meetings, provide written comments when requested to do so, etc.). They also will be expected to devote the resources necessary to ensure the ability of the working group to meet any assigned deadline(s). Members are expected to keep their management chain advised of working group activities and decisions to ensure that the agreed technical solutions do not conflict with their sponsoring organization's position when the subject being negotiated is presented to ARAC for a vote. Once the working group has begun deliberations, members will not be added or substituted without the approval of the assistant chair, the assistant executive director, and the working group chair. The Secretary of Transportation has determined that the formation and use of ARAC are necessary and in the public interest in connection with the performance of duties imposed on the FAA by law. [[Page 66524]] Meetings of ARAC will be open to the public. Meetings of the working groups will not be open to the public, except to the extent that individuals with an interest and expertise are selected to participate. No public announcement of working group meetings will be made. Issued in Washington, DC, on November 19, 1999. Anthony F. Fazio, Executive Director, Aviation Rulemaking Advisory Committee. [FR Doc. 99-30774 Filed 11-24-99; 8:45 am] BILLING CODE 4910-13-M

## Recommendation LetterPratt & Whitney 400 Main Street ---- --**~~** ----- -------------------1

East Hartford, CT 06108 

### July 18, 

### 2001
Federal Aviation Administration 

### 800 Independence Avenue, SW Washington, D.C. 

### 20591 Attention: Mr. Thomas McSweeny, Associate Administrator for Regulation and Certification Subject: ARAC Report, FAR 

### 25.415, Ground Gust Conditions Dear Tom: The Transport Airplane and Engine Issues Group is pleased to forward the attached Report (including proposed NPRM and AC) for FAR 

### 25.415, Ground Gust Conditions to the FAA as an ARAC recommendation. This report was prepared by the Loads and Dynamics HWG under the "Fast Track" tasking. Also attached are comments and concerns from the Airline Pilots Association that were provided at TAEIG meetings. These concerns relate to assumptions made as a part of the proposed Part 

### 25 design requirements and the relationship to operational requirements. The ALPA document is provided for FAA consideration during the processing ofthis report. Sincerely yours,

# (~/lt\A**g,-~ r.~~t**  Assistant Chair, TAEIG Copies*:

*Ietter only

crb071801 

### Larry Hanson
- Gulfstream Chuck Huber
- FAA-NWR Effie Upshaw
- FAA-Washington, D.C. Jim Bettcher
- ALPA Jim Wallace
- ALPA Jill DeMarco
- FAA-NWR

## Acknowledgement Letter

### SEP 27 

## 2001

Mr. Craig 

### R. Bolt Assistant Chair, Aviation Rulemaking Advisory Committee Pratt &Whitney 400 Main Street East Hartford, CT 06108 Dear Mr. Bolt: This letter acknowledges receipt ofyour July 18, letter transmitting a recommendation for harmonizing 

### § 25.415, ground gust conditions. I would like to thank the Aviation Rulemaking Advisory Committee particularly those members associated with the Transport Airplane and Engine (TAE) Issues and the Loads and Dynamics Harmonization Working Group for their cooperation in completing the working group report in a timely manner. The recommendation will be forwarded to the Transport Airplane Directorate for review. Progress on the documents will be reported at the TAE meetings. Sincerely,



### ORGINIALSIGNED BY



### ANTHONYF. FAZIO Anthony F. Fazio Director, Office of Rulemaking ARM-209:E Upshaw:fs:9/25/01 :PCDOCS #16015 cc: ARM-1/20/200/209; APO-300/320, ANM-115/110 File #ANM-00-552-A CONTROL NO. 20012470-0

## RecommendationLoads and Dynamics ARAC WGReport for 25.415 Ground Gust 18 June2001 Harmonization (Category 3) andNew Projects 1- Whatis underlying safety issue to be addressed by the FAR/JAR? CFR 14 Amendment 25-91 increased the ground gust velocity requirement for §25.415 from 60 MPH (52 Knots) TAS to 65 KTAS. Howeverbased on several incidents that have occurred to aircraft on the United Kingdom register and at least one aircraft on the US register, it has been determined that the effects ofcontrol system flexibility can lead to internal loads greater than those corresponding to the hinge moments prescribed by §25.415. Although damage from ground gusts may not be an immediate hazard, the rule is intended to prevent damage to the control system that may not be detected before takeoff. The JAA Structures Study Group has developed a draftNPA25C-284 

### in response to this issue. The L&D HWG was assigned the task ofharmonizing FAR and JAR 25.415 as aFast Track Category 1item. However the existence ofthe draft NPA25C-284 and the safety issues addressed therein caused the L&D HWGto successfully petition for a change in the Fast rack Category to Category 3. Currently the rules § 25.391 through §25.415 are convoluted and confusing and have lead to differing interpretations being utilized as the basis for compliance.

2 - Whatarethe currentFARandJARstandardsrelative to this subject? Current FARtext: (a) The control system must be designed as follows for control surface loads due to ground gusts and for taxiing downwind: (1) The control systembetween the stops nearest the surfaces and the cockpit controls must be designed for loads corresponding to the limit hinge moment ofparagraph (a)(2) ofthis section. These loads need not exceed

- (i) The loads corresponding to the maximum pilot forces in 25.397(c) for any pilot alone or (ii) 0.75 times these maximum loads for each pilot when the pilot forces are applied in the same direction (2) The control system stops nearest the surfaces, the control system locks and the parts ofthe system (ifany) between these stops and locks and the control sutface horns, must be designed for the limit hinge moments H, in foot pounds, obtained from the formula, H = .0034KV2cS, where_ V

### =65 (wind speed in knots)--------
------- --

K = limit hinge moment factor for ground gusts derived in paragraph (b) ofthis section. c = mean chord ofthe control surface aft ofthe hinge line (ft); S

### =area ofthe control surface aft ofthe hinge line (sq ft); (b) The limit binge moment factor Kfor ground gusts must be derived as follows:
Surface K Position ofcontrols (a) Aileron

--------------- 0.75 Control column lockedor lashedinmid-p()sition. (b) Aileron

------------ *±O.50 Ailerons atfull throw. (c) Elevator------------ *±O.75 (c) Elevatorfull down. (d) Elevator------------- *±O.75 (d) Elevatorfull up. (e) Rudder----------------- 0.75 (e) Rudder inneutral. (1) Rudder--------------- 0.75 (1) Rudder at full throw.

* Apositive value of

### Kindicates a moment tending to depress the surface, while a negative value ofK indicates amoment tending to raise the surface. Current JAR text (As ofChange 15): Same as above FARtext. 2a

- Hno FARorJAR standard exists, what means have been used to ensurethis safety issue is addressed? Not applicable.

3 - What arethedifferences in the FAA and JAA standards orpolicy and whatdo these differences result in? There are no differences in current standards. Itis however a JAA policy that for aircraft where the dynamic response ofcontrol systems may be significant for ground gusts, the dynamic effects ofcontrol systems be taken into account. The JAA requires consideration ofthe control systems "locked" while moored and ''unlocked'' when taxing downwind. 4 - What, ifany, are the differences in the current means ofcompliance? Discussed initem 3. 5 - What is the proposed action?

### Develop an NPRM with the following requirements: § 25.391 Control surface loads: general. The control surfaces must be designed forthe limit loads resulting from the flight conditions in §§ 25.331, 25.341 (a) and (b), 25.349 and 25.351 aRd the {JnnlAd {JYst OORditioRS iR SSG. 25.415, considering the requirements for**~**

(a) Loads parallel to hinge line, in § 25.393; (b) Pilot effort effects, in § 25.397; (c) Trim tab effects, in § 25.407; (d) Unsymmetrical loads, in § 25.427; and (e) Auxiliary aerodynamic surfaces, in § 25.445. § 25.395 Control Systems (a) (retain current text) (b) The system limit loads of par@graph (a), exGept the loads F8suitiRg wOn:! gFOynd gYsts, need not exceed the loadsthat can be produced by the pilot (or pitots) and by automatic or power devices operating the controls. (c) (retain current text) § 25.415 Ground gustconditions. (a) The flight control systems and surfaces must be designed forthe limit loads generated when the aircraft is subjected to a horizontal 65 knots ground gust from any direction, while taxiing with the controls locked and unlocked and while parked with the controls locked. (b) The control system and surface loads due to ground gust may be assumed to be static loads and the hinge moments H, in foot pounds, must be computed from the fonnula,

where: K

## = hinge moment factor for ground gusts derived in paragraph (c) ofthis paragraph Po

# = density of air at sea level = .0023769 (slugslfe)

## = .0023769**(I~Sec21** ft4) V 

### =65 knots= 109.71 fps relative tothe aircraft S = area ofthe control surface aft ofthe hinge line (ft2) c

## = mean aerodynamic chord ofthe control surface aft ofthe hinge line (ft) (c) The hinge moment factor K for ground gusts must be taken from the following table: Surface K Position of controls (a) Aileron**-~-----------** 0.75 Control column locked or lashed in mid-position. (b) Aileron ------------.--- *:to.50 Ailerons at full throw. (c)**Elevator--------~-** *±0.75 (c) Elevatorfull down. (d)**Elevator~-----------~-** *:to.75 (d) Elevatorfull up. (e) Rudder----------- 0.75 (e) Rudder in neutral. (f) Rudder-------------- 0.75 (f) Rudder at full throw.

* A positive value ofKindicates a momenttending to depress the surface, while a negative value ofKindicates a moment tending to raise the surface.(d) The computed hinge moment of paragraph (b) must be used to determine the limit loads due to ground gust conditions for the control surface. A 1.25 factor on the computed hinge moments must be used in calculating limit control system loads. (e) Where control system flexibility is such that the rate of load application in the ground gust conditions might produce transient stresses appreciably higherthan those corresponding to static loads, in the absence of a rational analysis an additional factor of 1.6 must be applied to the control system loads of paragraph (d) to obtain limit loads. Ifa rational analysis is used, the additional factor must not be less than 1.20. (f) Forthe condition ofthe control locks engaged, the control surfaces, the control system locks and the parts ofthe control systems (if any) between the surfaces and the locks must be designed to the respective resultant limit loads. Where control lockS are not provided then the control surfaces, the control system stops nearest the surfaces and the parts ofthe control systems (if any) between the surfaces and the stops must be designed to the resultant limit loads. Ifthe control system design is such as to allow any part ofthe control system to impact with the stops due to flexibility, then the resultant impact loads must betaken into account in deriving the limit loads due to ground gust. (9) Forthe condition oftaxiing with the control locks disengaged, the following apply: (1) The control surfaces, the control system stops nearest the surfaces and the parts of the control systems (if any) between the surfaces and the stops must be designed to the resultant limit loads. (2) The parts ofthe control systems between the stops nearest the surfaces and the cockpit controls must be designed to the resultant limit loads, except that the parts ofthe control system where loads are eventually reacted by the pilot need not exceed: (i) The loads corresponding to the maximum pilot loads in § 25.397 (c) for each pilot alone; or (ii) 0.75 times these maximum loads for each pilot when the pilot forces are applied in the same direction. Foreach proposed change from the existing standard, answerthefoUowing questions: 6 - What should the harmonized standard be? See question 5. 7 - Bowdoes this proposed standard address the underlying safety issue (identified under#l)? 

### An improved standard has been developed that removes ambiguities in the current regulations and also accounts for dynamic affects by requiring the simple use offactors that are applied to the loads. An additional factor is required for systems where dynamic effects may be significant. The approach is simple and will lead to consistent design requirements.

8 - Relative to the currentFAR, does the proposed standard increase, decrease, or maintain the same level ofsafety? Explain.Current level ofsafety is increased due to the elimination ofconfusing requirements and by requiring higher control system and control surface design loads requirements for ground gust where it is appropriate. 9 - Relative to currentindustry practice, does the proposed standard increase, decrease, ormaintain the same level ofsafety? Explain. Increases the level ofsafety. Many manufacturers have designed their control systems to account for the dynamic effects for ground gust. However such analyses are very complex and lead to a wide range ofpossible results. The proposed changes are based upon factors that are applied to static analyses that will result in more reliable and uniform certification compliance. Dynamic analysis is still allowed as an option. However, when dynamic analysis is used minimum increases in loads due to dynamic effects are specified as afloor design level. 10

- What otheroptions have been considered andwhy werethey not selected? The JAA has required that the dynamic effects be accounted for by analysis. Due to the difficulties in doing such analysis, the HWGbelieves that the proposed standard is more appropriate. The L&DHWG reviewed the issue ofpotential control system damage during aircraft ground operations in ground gust conditions. An issuehad been raised regarding the potential for control system damage due to impact ofthe surfaces with the stop with the gust locks disengaged and with the control system not constrainedby the pilot. The concern is for reversible systems such as manual systems that do not have a significant amount ofdamping. The following conclusions have been reached: 1. The design load level has been increased by afactor ofat least 2.5 relative to earlier design requirements for systems with significant flexibility. 2. The proposed rule addresses the effect ofcontrol surface impact with the control stops for flexible systems. 3. TheL&DHWG does not feel that itis reasonable to operate an aircraft with manual control systems in design ground gust conditions with thepilot not constraining the control systems. This is supported by the FAAFlying HandbookFAA-H-8083-3 Chapter 2 for Ground Operations. 4. Some aircraft have operational procedures that require the gust lockto remain engaged until shortly before takeoff.5. The L&D HWGis not aware ofconclusive evidence offailure ofthe control systems when the pilot is not constraining the flight controls. 6. Therefore the L&DHWGbelieves that the requirements that have been developed for the instance where the pilot constrains theflight controls are adequate. 7. The L&DHWG recommends that the TAEIG considerthe need for additional operational procedures or the development ofpilot informative material regarding the need for constraint ofthe flight controls during ground operations. 11 •Who would be affected by the proposed change? Airplane manufacturers. 12

- To ensure harmonization, what current advisory material (e.g., ACJ,AMJ,AC, policy letters) needs to be included in therule text orpreamble? Anew ACJ is recommended based upon the draft AC perbelow. 13

- Is existing FAA advisory material adequate? Ifnot, what advisory material should be adopted? There is no existing FAA advisory material. Adraft AC 25.415-1 , as attached, is proposed along with a corresponding ACI. 14

- Bow does the proposed standard compareto the currentICAO standard? The current ICAO standard has no specific criteriafor ground gust analysis.

15

- Does the proposed standard affect otherBWG's? No. 16

- Whatis thecost impact ofcomplying with theproposed standard? Economic analysis still tobe done but it is expected to be small in comparisonto standard industry practice. 17.

- Ifadvisory orinterpretivematerial is to be submitted, document the advisory orinterpretive guidelines. Ifdisagreement exists, document the disagreement. Draft Advisory Circular AC 25.415-1 is submitted.18••Does tbe HWGwisb to answer any supplementary questions specific to tbis project? 

### Not at this time. 19.

- Does tbe HWGwant to review tbedraft NPRM at "Pbase4" priorto publication in tbeFederal Register? 

### Yes 20. -Inligbt oftbe information provided in tbis report, does tbeHWGconsider tbat tbe "FastTrack" process is appropriatefor tbis rulemaking project, oris tbe projecttoo complex orcontroversial for tbeFast TrackProcess? Explain. 

### It is appropriate for the "Fast Track" process.D-R-A-F-T
[4910-13] DEPARTMENT OFTRANSPORTATION FederalAviation Administration 14 CFRPart 25 (Docket No. ; NoticeNo. ] RIN: 2120- Ground Gust Conditions. AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Notice ofproposed rulemaking (NPRM). Rev 6-20-01

SUMMARY: The Federal Aviation Administration proposes to amend the airworthiness standards for transport category airplanes in regard to ground gust design conditions for control systems and surfaces. The proposed amendment would revise the regulations to require an additional multiplying factor on design loads to account for dynamic loading conditions. Several near accidents have occurred as aresult ofthe dynamic effects of ground gusts conditions which have caused damage to control systems that was not detected before take-off. This proposal is based on arecommendation by the Aviation Rulemaking Advisory Committee (ARAC) and is intended to ensure that control systems and surfaces can withstandthe ground gust conditions expected in service. The Joint Aviation Authorities (JAA) ofEurope are considering a similarproposal to amend the Joint Aviation Requirements (JAR-25). Adopting this proposal would maintain similar requirements between the airworthiness standards ofthe U.S. and the Joint Aviation Requirements ofEurope. DATES: Send your comments on orbefore [Insert date 60 days after date ofpublication in the Federal Register.] ADDRESSES:D-R-A-F

... T Rev 6

..20-01

Comments: Address your comments to Dockets Management System, U.S. Department ofTransportation Dockets, Room Plaza 401,400 Seventh Street SW., Washington, DC 20590-0001. You must identify the docket number

_______at the beginning ofyour comments, and you should submit two copies ofyour comments. Ifyou wish toreceive confirmationthat the FAA has received your comments, please include a self-addressed, stamped postcard on which the following statement is made: "Comments to DocketNo. ." We will date-stamp the postcard and mail it backto you. You also may submit comments electronically to the following Internet address: http://dms.dot.gov. Public Docket: You may review the public docket containing comments tothis proposed regulation at the Department ofTransportationDockets Office, located on the plaza level ofthe NassifBuilding at the above address. You may review the public docket in person at this address between 9:00 a.m. and 5:00 p.m., Monday through Friday, except Federal holidays. Also, you may review the public dockets on the Internet at http://dms.dot.gov. InformationDocket: In addition, the FAAis maintaining an ''information docket" ofcomments in the Transport Airplane Directorate, FAA, Aircraft Certification Service, Program Management Branch (ANM-114), 1601 Lind Avenue SW., Renton, Washington 98055-4056. You may review the information docket in person at this address between 7:30 a.m. and 4:00 p.m., Monday through Friday, except Federal holidays. FORFURTHERINFORMATION CONTACT: James Haynes, FAA, Airframe and Cabin Safety Branch (ANM-115), Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Ave S.W., Renton, Washington 98055-4056; telephone (425) 227- 2131; facsimile (425) 227-1320; e-mail: jim.haynes@faa.gov. SUPPLEMENTARY INFORMATION: 2

### O-R-A-F-T Rev 6-20-01

Bow Do I Submit Comments to this NPRM? Interested persons are invited to participate inthe making ofthe proposed action by submitting such written data, views, or arguments, as they may desire. Comments relating to the environmental, energy, federalism, or economic impact that might result from adopting the proposals in this document are also invited. Substantive comments should be accompanied by cost estimates. Comments must identifYthe regulatory docket number and be submitted in duplicate to the DOT Rules Docket address specified above. All comments received, as well as areport summarizing each substantive public contact with FAA personnel concerning this proposed rulemaking, will be filed inthe docket. The docket is available for public inspectionbefore and afterthe comment closing date. We will consider all comments received on orbefore the closing date before taking action onthis proposed rulemaking. Comments filed late will be considered as far as possible without incurring expense ordelay. The proposals in this document may be changed in light ofthe comments received. Bow Can I Obtain a Copy ofthis NPRM? You may download an electronic copy ofthis document using a modem and suitable communications software from the FAA regulations section ofthe Fedworld electronic bulletin board service (telephone: 703-321-3339); the Government Printing Office (GPoys electronicbulletinboard service (telephone: 202-512-1661); or, if applicable, the FAA's Aviation Rulemaking Advisory Committee bulletin board service (telephone: 800-322-2722 or 202-267-5948). Internet users may access recently published rulemaking documents at the FAA's web page at http://www.faa.gov/avr/armlnprmlnprm.htm orthe GPO's web page at http://www.access.gpo.gov/nara.

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## D-R-A-F-T Rev 6-20-01
Any person may obtain a copy ofthis document by submitting arequest tothe Federal Aviation Administration, Office ofRulemaking, ARM-I, and 800 Independence Avenue, SW., Washington, DC 20591; orby calling 202- 267-9680. Communications must identify the docket number ofthis NPRM. Any person interested in being placed onthe mailing list for future rulemaking documents should request from the above office a copy ofAdvisory Circular 11-2A, ''Notice ofProposed Rulemaking Distribution System," which describes the application procedure. WhatAre the Relevant Airworthiness Standards in the United States? Inthe United States, the airworthiness standards for type certification oftransport category airplanes are contained in 14 Code ofFederal Regulations (CPR) part 25, commonly referred to as the Federal Aviation Regulations (FAR). Manufacturers of transport category airplanes must show that each airplane they produce ofa different type design complies with the appropriate part 25 standards. These standards apply to:
• airplanes manufactured within the U.s. for use by u.S.-registered operators, and
• airplanes manufactured in other countries and imported tothe U.S. under a bilateral airworthiness agreement. WhatAretheRelevant Airworthiness Standards in Europe? In Europe, the airworthiness standards for type certification oftransport category airplanes are contained in Joint Aviation Requirements (JAR)-25, which are based on part 25. These were developed by the Joint Aviation Authorities (JAA) ofEurope to provide a
common set ofairworthiness standards within the European aviation community. Twentythree European countries accept airplanes type certificated to the JAR-25 standards, including airplanes manufactured in the U.S. that are type certificated to JAR-25 standards for export to Europe. 4D-R-A-F-T Rev 6-20-01

Whatis "Harmonization" and How Did it Start? Although part 25 and JAR-25 are very similar, they are not identical in every respect. When airplanes are type certificated to both sets ofstandards, the differences between part 25 and JAR-25 can result in substantial additional costs to manufacturers and operators. These additional costs, however, frequently do not bring about an increase in safety. 

### In many cases, part 25 and JAR-25 may contain different requirements to accomplish the same safety intent. Consequently, manufacturers are usually burdened with meeting the requirements ofboth sets ofstandards, although the level ofsafety is not increased correspondingly. Recognizing that a common set ofstandards would not onlybenefitthe aviation industry economically, but also maintain the necessary high level ofsafety, the FAA and the JAAbegan an effort in 1988 to "harmonize" theirrespective aviation standards. The goal ofthe harmonization effort is to ensure that:
• where possible, standards do not require domestic and foreign parties to manufacture
or operateto different standards for each country involved; and
• the standards adopted are mutually acceptable to the FAA and the foreign aviation authorities. Both the FAA and the JAA consider "harmonization" ofthe two sets ofstandards
ahigh priority. What is ARAC andWhatRole Does itPlay in Harmonization? After initiating the first steps towards harmonization, the FAA and JAA soon realized that traditional methods ofrulemaking and accommodating different administrative procedures was neither sufficient nor adequate to make appreciable progress towards fulfilling the goal ofharmonization. The FAAthen identified the Aviation Rulemaking Advisory Committee (ARAC) as an ideal vehicle for assisting in

5

## D-R-A-F-T Rev 6-20"()1


### resolving harmonization issues, and, in 1992, the FAAtasked ARAC to undertake the entire harmonization effort. The FAAhad fonnally established ARAC in 1991(56 FR2190, January 22, 1991), to provide advice and recommendations concerning the full range ofthe FAA's safetyrelated rulemaking activity. The FAA sought this advice to develop betterrules in less overall time and using fewer FAAresources than previously needed. The committee provides the FAA firsthand infonnation and insight from interested parties regarding potential new rules orrevisions ofexisting rules. There are 64 member organizations onthe committee, representing a wide range ofinterests withinthe aviation community. Meetings ofthe committee are open to the public, except as authorized by section 10(d) ofthe Federal Advisory Committee Act. The ARAC establishes working groups to develop recommendations for resolving specific airworthiness issues. Tasks assigned to working groups are published inthe Fedetal Register. Although working group meetings are not generally opento the public, the FAA solicits participation in working groups from interested members ofthe public who possess knowledge or experience in the task areas. Working groups report directly to the ARAC, and the ARAC must accept a working group proposal before ARAC presents the proposal to the FAA as an advisory committee recommendation. The activities ofthe ARAC will not, however, circumventthe public ruIemaking procedures; nor is the FAAlimited to the rule language "recommended" by ARAC. If 

### the FAA accepts an ARAC recommendation, the agency proceeds withthe normal public rulemaking procedures. Any ARAC participationin arulemaking package is fully disclosed in the public docket. Whatis the Status ofthe Harmonization Effort Today? 

### Despite the work that ARAC has undertaken to address harmonization, there remain alarge number ofregulatory differences between part 25 and JAR-2S. The current 6-------------- ------


### D-R-A-F-T Rev 6-20-01

harmonization process is extremely costly and time-consuming for industry, the FAA, and the JAA. Industry has expressed a strong desire to conclude the harmonization program
as quickly as possible to alleviate the drain on theirresources and to finally establish one acceptable set ofstandards. Recently, representatives ofthe aviation industry [including Aerospace Industries Association ofAmerica, Inc. (AlA), General Aviation Manufacturers Association (GAMA), and European Association ofAerospace Industries (AECMA)] proposed an accelerated process to reach harmonization. These representatives recommended that the FAA and JAA harmonize differences between parallel part 25 and JAR-25 standardsby accepting the more "stringent" ofthe two standards. "Stringent," inthis case, indicates the relative higher level ofsafety, orgreater applicability to modem technology, between a part 25 standard and the parallel JAR-25 standard. Aviation industry groups further refined their proposed processby suggesting that the 42 part 25 standards that have already been tasked to ARAC for harmonizationbe divided into three categories: Category 1: Envelope

- Forthese standards, parallel part 25 and JAR-25 standards would be compared, and harmonization would be reached by accepting the more stringent ofthe two standards. In some cases, it may be necessary to incorporate parts of boththe part 25 and JAR standard to achieve the final, more stringent standard. (This may necessitate that each authority revises its current standard to incorporate more stringent provisions ofthe other.). Category 2: Completed ornearcomplete

- Forthese standards, ARAC has reached, or has nearly reached, technical agreement or consensus onthe new wording of the proposed harmonized standards. Category 3: Harmonize

- Forthese standards, ARAC is not neartechnical agreement on harmonization, and the parallel part 25 and JAR-25 standards cannotbe 7- ----**-~ ~** **~-------------L-** ___ -.-J


## D-R-A-F-T Rev 6-20-01
"enveloped" (as described under Category 1) for reasons ofsafety orunacceptability. A standard developed under Category 3 would be mutually acceptable to the FAAand JAA, with a consistent means ofcompliance. Whatis the "FastTrackHarmonization Program"? Inlight ofthe general agreement among the affected industries and authorities to expedite the harmonization program, and a willingness to consider «enveloping" ofparallel standards, the FAA and JAA in March 1999 agreed upon a method to achieve these goals. This method, which the FAA has titled "The Fast Track Harmonization Program," is aimed at expediting the rulemaking process for harmonizing not only the 42 standards that
are currently tasked to ARAC for harmonization, but approximately 80 additional standards for part 25 airplanes. The FAAinitiated the Fast Trackprogram on November 26, 1999 (64 FR66522), by re-tasking ARAC to accomplish the following:

• Review a list ofpart**25/JAR~25** standards (approximately 120 parallel pairs) identified by industry, FAA, and JAA as having differences that should be harmonized in orderto establish one single set ofstandards that represent the highest level ofsafety.

• Identity changes necessary to the standardstoharmonize part 25 and**JAR~** 25.

• Submitto the FAA atechnical report on each standard and recommend what the requirements ofthe harmonized standard should be. The FAAthen considers the recommendations submitted by ARAC and initiates rulemaking action, as appropriate, based on those recommendations. As implemented, the Fast Trackprogram achieves its aims by:
• considering the fundamentals ofthe industry proposals,
• defining a process for expeditiously adopting the harmonized requirements, 8

### D·R

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• maintaining an emphasis on using ARAC in making a group decision on the harmonization proposal, and

• incorporating an improved ARAC rulemaking process that does not overburden the FAA and industry due to additional workload. DISCUSSION OFTHE PROPOSAL How Does This Proposed Regulation Relate to "FastTrack"? This proposed regulation results from the recommendations ofARAC submitted underthe FAA's Fast TrackHarmonization Program. Although the existing standards for §25.415 "Ground gust conditions" are identical between FAR and JAR, the Joint Aviation Authorities has raised a safety issue as aresult ofsome near accidents in Europe and they have been inthe process ofpreparing a notice ofproposed rulemaking that would improve the standard. It has also been recent JAA policy to request manufacturers to address these safety concerns during certification. Since this has created a difference in practice, this effort was included as part ofthe fast track program (category 3)in orderto
ensure a harmonized proposal would be achieved to address the safety concerns. Inthis notice, the FAAproposes to amend §25.415, concerning ground gust conditions. The JAA plans a similarrevision to the JAR. Whatis the Underlying Safety Issue Addressed by the Current Standards? The current standard is intended to protect the airplane flight control system from damage due to ground winds and gusts. Although damage from ground gusts may not be
an immediate hazard, the rule is intended toprevent damage to the control systemthat may not be detected before take-off The current airworthiness standards contained in 14 CFRpart 25 require that control systems and surfaces be designed for ground gusts and taxiing downwind. This implies two conditions. One in which the airplane is parked and unattended with gust

9

### O-R-A-F-T Rev 6-20-01

locks (ifapplicable) engaged, and the other, ataxi condition with the gust locks disengaged with the controls systempowered (ifapplicable) and/orrestrained by the pilot. The requirement to considerthe effects ofground gusts has been applied to transport airplane since 1950. The purpose ofthe requirement has been to protect the flight control system from excessive peak ground wind loads while the airplane is parked
or while taxiing downwind. Although damage by ground gusts may not be an immediate hazard, the rule is intended to prevent damage to the control systems that may go unnoticed until the airplane is airborne. For developing the original regulation, the control surface load distribution was considered to be triangularwith the peak at the trailing edge representing reversed flow overthe control surface. This assumption, along with assumptions about the wind approach angle and typical control surface geometries were developed into a table ofhinge moment factors and set forth inthe regulation. These hinge moment factors have been carried forward tothe existing table in §25.415. The maximum design wind speed was originally set at a maximum of88 feet per second (52 knots) underthe presumption that higher speeds were predictable conditions and the aircraft
owner could take additional precautions (such as sheltering, additional tiedowns, or external bracing) beyond engaging the standard gust locks. Amendment 25-91 (62 FR 40704) incorporated a new condition into the FAR forjacking and tie down loads which was similarto the existing Joint Aviation Requirement in paragraph 25.519. Those conditions required consideration ofthe airplane in a moored orjacked conditionin peak wind speeds up to 65 knots. 

### In order tobe consistent in the treatment ofground winds, section 25.415, concerning ground gust conditions on control surfaces, was increased to 65 knots.

10

### D-R-A
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What are the Current JAR-25 and 14 CFR Standards? The currenttexts of 14 CFR §25.415 (amendment 25-91) and JAR-25 (change 15) are essentially identical: 25.415 Ground gust conditions. (a) The control system must be designed as follows for control surface loads due to ground gusts and taxiing downwind: (1) The control systembetween the stops nearest the surfaces and the cockpit controls must be designed for loads corresponding to the limit hinge moments H of paragraph (a)(2) ofthis section. These loads need not exceed-- (i) The loads corresponding to the maximum pilot loads in Sec. 25.397(c) for each pilot**alone~** or (ii) 0.75 times these maximum loads for each pilot when the pilot forces are applied inthe same direction. (2) The control system stops nearest the surfaces, the control system locks, and the parts ofthe systems (ifany) between these stops and locks and the control surface horns, must be designed for limit hinge moments, H, 

### in foot pounds, obtained from the formula, H == .0034KV 2cS, where_ V := 65 (wind speed in knots) K

### =limit hinge moment factor for ground gusts derived in paragraph (b) ofthis section.
c:= mean chord ofthe control surface 

### aft ofthehinge line**(ft)~** S :=area ofthe control surface 

### aft ofthe hinge line (sq**ft)~]** (b) The limit hinge moment factor K for ground gusts must be derived as follows:

11

### D·R·A·F·T
Surface (a) Aileron

---------- (b) 

### Aileron

---------- (c) Elevator

---------- (d) Elevator------

..--- (e) Rudder----------- (f) 

### Rudder---------- K 0.75 *±O.50 *±0.75 *±0.75 0.75 0.75 Rev 6·20"()1


### Position ofcontrols Control column locked or lashed in mid-position. Ailerons at full 

### throw. (c) Elevator full down. (d) Elevator full up. (e) Rudder in neutral. (f) 

### Rudder at full 

### throw.


## *

Apositive value ofK

### indicates amoment tending to depress the surface, while a negative value of

### Kindicates amoment tending to raise the surface.
How Have the Standards Been Applied? 

### Most ofthe experience in complying withthe requirement are for airplanes with certificationbases priorto amendment 25-91 (or JAR Change 15) so they were required tobe designs to a speed of52 knots rather than the existing 65 knots. The requirement has been applied as a static "steady" load condition to develop loads on the control surfaces, and loads inthe control systembetweenthe pilots controls and the surface. Two conditions are considered, one with the aircraft parked and unattended with any available gust locks engaged, and the other with the aircraft taxiing with controls unlocked and restrained by the pilot, orcontrol system power, orboth. Section 25.391 "Control SystemLoads", requires an additional mUltiplying factor of1.25 onthe control system loads due to the control surface aerodynamic binge moments butthis regulation is confusing as to its applicability to the hinge moments derived for ground gusts and many manufacturers have not used this additional multiplying factor for the ground gust condition. Why is a Revision to the Current Standards Needed? 

### The ground gust requirement was never intended to completely protectthe airplane against all 

### possible ground wind conditions that may occur. Wind conditions with 12O-R-A-F-T Rev 6-20-01
gusts in excess ofthe original design speed of52 knots are relatively common around the world, however, they are considered to be reasonably predictable and the airplane operator has been expected to take additional precautions to protect the airplane if necessary. As airplanes have became larger, and operations more demanding, airplanes have become more difficult and inconvenient to protect in service and the need for higher ground gust design speeds has become evident. The speeds were increased to 65 knots in amendment 25-91 and that speed was derived from an existing design speed for ground wind conditions for airplanes that were tied down or onjacks. Several incidents that have occurred to aircraft on the United Kingdom register and at least one aircraft onthe US register where the aircraft sustained severe ground gust damage to the flight control system which went undetected until aftertakeoff. These incidents occurred on airplanes withunpowered mechanical controls with significant flexibility between the contol surface and the gust locking devices. This flexibility allows dynamic loads, well in excess ofthe static design gust loads, to occur. Since amendment 25-91 has already raised the requirement from 52 knots to 65 knots (a 56 percent increase in design load) a considerable improvement in the resistance to ground gusts has already been achieved. There remains a need for clarificationto
ensure the application ofthe existing 1.25 factor in section 25.391 for the the ground gust condition and to provide additional design criteria for those airplanes which are suscepttbleto dynamic load amplificationbecause ofthe control system and gust lock configuration. What Is the Proposed Action and How Does ItAddress the Underlying Safety Issue? This proposal would revise § 25.415 to stand alone in regard to the required mUltiplying factors and provide and additional multiplying factor to account for dynamic amplification. The design conditions would be set forth as two design cases; one with gust locks engaged and another as ataxiing case with the gust locks disengagedbut 13O-R-A-F-T Rev 6-20"()1

controls restrained by the pilot and/or powered system. The 1.25 factor would apply to the design hinge moments to obtain static limit loads for the design ofthe control system. Afurther multiplying factor of1.6 (total multiplying factor of2.0)would be applied for those parts ofthe control system where dynamic effects could be significant. These actions should eliminate any confusion as to the required multiplying factors and the net effect (including the speed increase resulting from amendment 25-91 and use ofthe 1.25 factor) overthe past practices could be on the order ofa 95 percent increase in the static ground gust design loads for the control system. Forthose parts ofthe control systems where dynamic amplification is ofconcern atotal load increase ofover200 percent in the required design load may be realized along with a coresponding increase in strength. These load levels should be sufficientto account for the expected ground gust loads that
are likely to occurin operation. These changes would provide the greatest affect on mechanical, unpowered, control systems which have shown the greatest susceptability to damage. Powered control system normally possess natural protection from ground gusts by means oftheir hydraulic actuators. What Changes Would Be Made to the Current 14 CFR Sections 25.391 and 25.395 would be revised to eliminate any reference to ground gust conditions and section 25.415 would stand on its own in regard to the design multiplying factors. Section 25.415 would include the 1.25 multiplying factor currently contained in section 25.395. An additional multiplying factor of1.6 would berequired for parts ofthe control system where dynamic effects are expected tobe significant. The rule would be organized to clarifYthe cases to be considered and to identifY the components and parts ofthe control system and surface to which each ofthe conditions apply. The JAA plans parallel changes to JAR-2S.

14Rev 6-20-01

Is Existing FAA Advisory MaterialAdequate? The FAAis preparing toissue a new proposed Advisory Circular 25.415-1, "Ground gust conditions," to describe a means ofcompliance with the proposed regulation, which would meet the intended level ofsafety and promote consistent and effective application ofthe proposed revised standards. Public comments concerning the proposed AC are invited by separate notice published elsewhere in this issue ofthe Federal Register REGULATORYANALYSES AND ASSESSMENTS PaperworkReduction Act In accordance with the PaperworkReduction Act of1995 [44 U.S.C. 3507(d)], the FAA had determined there are no requirements for information collection associated with this proposed rule. Compatibility with ICAO Standards In keeping with U.S. obligations underthe Convention on International Civil Aviation, it is FAApolicy to comply with International Civil Aviation Organization (ICAO) Standards and Recommended Practices to the maximum extent practicable. The FAA determined that there are no ICAO Standards and Recommended Practicesthat correspond to this proposed regulation. Regulatory Evaluation Summary Changes to Federal regulations must undergo several economic analyses. First, Executive Order 12866 directs that eachFederal agency shall propose or adopt a regulation only upon areasoned determination that the benefits ofthe intended regulation justify its costs. Second, the Regulatory Flexibility Act of1980 requires agencies to analyze the economic effect ofregulatory changes on small entities. Third, the Office of Management and Budget directs agencies to assess the effects ofregulatory changes on international trade. And fourth, the Unfunded Mandates Reform Act of1995 (Pub. L. 15

### O-R-A-F-T Rev 6-20-01
104-4) requires agencies to prepare a written assessment ofthe cots, benefits, and other effects ofproposed orfinal rules that include aFederal mandate likely toresult inthe expenditureby State, local, ortribal governments, in the aggregate, orby the private sector, of$100 million or more annually (adjusted for inflation). In conducting these analyses, the FAA has determined that this proposed rule: (1) would generate benefits thatjustify its costs and would not be "a significant regulatory action" as defined in section 3(f) ofExecutive Order 12866 and, therefore, is not subject to review by the Office ofManagement and Budget; (2) would not have a significant impact on a substantial number ofsmall entities; (3) would not constitute abarrierto international trade; and (4) would not contain a significant intergovernmental orprivate sectormandate. These analyses, available in the docket, are summarizedbelow. The FAA invites the public to provide comments and supporting data on the assumptions made in this evaluation. All comments received will be considered in the 

### final regulatory evaluation. Initial Regulatory Flexibility Determination The Regulatory Flexibility Act of1980 (RFA) establishes "as a principle of regulatory issuance that agencies shall endeavor, consistent with the objective ofthe rule and ofapplicable statutes, to fit regulatory and informational requirements to the scale of the business, organizations, and governmentaljurisdictions subjectto regulation." To achieve that principle, the Act requires agencies to solicit and considerflexible regulatory proposals and to explainthe rationale for their actions. The Act covers a wide-range of small entities, including small businesses, not-for-profit organizations, and small governmentaljurisdictions. Agencies must perform a review to determine whether a proposed rule will have a significant economic impact on a substantial number ofsmall entities. Ifthe determination

16

### O-R-A-F-T Rev 6-20-01

is that it will, the agency must prepare aregulatory flexibility analysis as descnbed in the Act. However, ifan agency determines that a proposed orfinal rule is not expected to have a significant economic impact on a substantial number ofsmall entities, section 605(b) ofthe 1980 Act provides that the head ofthe 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. [APO to addeconomic evaluation here.

### J International TradeImpactAssessment The provisions ofthis proposed rule would have little or no impact ontrade for U.S. firms doing business in foreign countries and foreign firms doing business in the United States. Federalism Implications The regulation proposed herein would not have a substantial direct effect onthe States, on the relationship between the national Government and the states, or onthe distribution ofpower and responsibilities among the various levels ofgovernment. Therefore, in accordance with Executive Order 12612, it is determined that this proposal would not have sufficient federalism implications to warrant the preparation ofa federalism assessment. Unfunded Mandates Reform Act Title IT ofthe Unfunded Mandates Reform Act of1995 (the Act), codified in 2 U.S.C. 1501-1571, requires eachFederal agency, to the extent permitted by law, to prepare awritten assessment ofthe effects ofany Federal mandate in a proposed or final agency rule that may result in the expenditure by State, local, and tribal governments, in the aggregate, orby the private sector, of$100 million or more (adjusted annually for inflation) in anyone year. Section 204(a) ofthe Act, 2 U.S.C. 1534(a), requires the 17

### D-R
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Federal agency to develop an effective process to permit timely inputby elected officers (ortheir designees) ofState, local, and tribal governments on a proposed "significant intergovernmental mandate." A "significant intergovernmental mandate" underthe Act is any provision in aFederal agency regulation that will impose an enforceable duty upon State, local, and tribal governments, in the aggregate, of$100 million (adjusted annually for inflation) in anyoneyear. Section 203 ofthe Act, 2 U.S.C. 1533, which supplements section 204(a), provides that before establishing any regulatory requirements that might significantly oruniquely affect small governments, the agency shall have developed a plan that, among otherthings, provides for notice to potentially affected small governments, if any, and for a meaningful and timely opportunity to provide input in the development of regulatory proposals. This proposed rule does not contain aFederal intergovernmental orprivate sector mandate that exceeds $100 million in anyoneyear. EnvironmentalAnalysis FAA Order 1050.1D defines FAA actions that may be categorically excluded from preparation ofaNational Environmental Policy Act (NEPA) environmental assessment or environmental impact statement. 

### In accordance with FAA Order 1050.1D, appendix 4, paragraph 4(j), this rulemaking qualifies for a categorical exclusion. Energy Impact The energy impact ofthe proposed rule has been assessed in accordance with the Energy Policy and Conservation Act (EPCA) and Public Law 94-163, as amended (42 U.S.C.6362). Ithas been determined that it is not a majorregulatory action underthe provisions ofthe EPCA.

18D

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Regulations Affecting IntrastateAviation in Alaska Section 1205 oftheFAAReauthorization Act of 1996 (110 Stat. 3213)requires the Administrator, when modifying regulations 

### in Title 14 ofthe CFRin a manner affecting intrastate aviation in Alaska, to consider the extent to which Alaska is not served by transportation modes otherthan aviation, and to establish such regulatory distinctions

as he or she considers appropriate. Becausethis proposed rule would apply tothe certification offuture designs oftransport category airplanes and their subsequent operation, it could, ifadopted, affect intrastate aviation in Alaska. TheFAAtherefore specifically requests comments onwhetherthere isjustification for applying theproposed rule differently tointrastate operations in Alaska. List ofSubjects in 14 CFRPart25: Aircraft, Aviation safety, Reporting and record keeping requirements TheProposed Amendment In consideration ofthe foregoing, theFederal Aviation Administration proposesto amend part 25 ofTitle 14, Code ofFederal Regulations, as follows: Part25

.. AIRWORmlNESS 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 § 25.391 byremoving the reference to § 25.415 

### as follows: § 25.391 Control surfaceloads: general.:. The control surfaces must be designed for the limit loads resulting from the flight conditions in §§ 25.331, 25.341(a) and (b), 25.349 and 25.351, considering the requirements for_

(a) Loads parallel tohinge line, in § 25.393; (b) Pilot effort effects, in § 25.397; 19**-------~--~~~----~~- ---------------------~------------j**  

### D-R-A-F-T Rev 6-20-01

(c) Trimtab effects, in § 25.407; (d) Unsymmetrical loads, in § 25.427; and (e) Auxiliary aerodynamic surfaces, in § 25.445. 3. Amend paragraph (b) of§ 25.395 by removing the reference to § 25.415 and clarifying the reference to the limit loads ofparagraph (a) of§ 25.395. § 25.395 Control System 

## * * * (b) The system limit loads ofparagraph (a) need not exceed the loads that can be produced by the pilot (orpilots) and by automatic orpower devices operating the controls. 4. Revise § 25.415 "Ground gust conditions" to read as follows. 

### § 25.415 Ground gust conditions. (a) The flight control systems and surfaces must be designed for thelimit loads generated when the aircraft is subjected to a horizontal 65 knots ground gust from any direction, while taxiing with the controls locked and unlocked and while parked with the controls locked. (b) The control system and surface loads due to ground gust may be assumed tobe static loads and the binge moments H, in foot pounds, must be computed from the formula,

H=K 1I2poVfps2cS where: K = binge moment factor for ground gusts derived in paragraph (c) ofthis paragraph po 

## =density ofair at sea level = .0023769 (slugS/fl?) 

## =.0023769**(Ib~sec2/** ft4) V = 65 knots = 109.71 fps relative to the aircraft S

### =area ofthe control surface aft ofthe hinge line (fl?)
c = mean aerodynamic chord ofthe control surface aft ofthe binge line (ft) 20

### O-R-A-F-T Rev 6-20-01
(c) The hinge moment factor K for ground gusts must be taken from the following table: Surface K Position ofcontrols (a) Aileron

----------------- 0.75 Control column locked or lashed in mid-position. (b) Aileron

------------------ *±0.50 Ailerons at full throw. (c) Elevator----------------- *±0.75 (c) Elevator full down. (d) Elevator---------------- *±0.75 (d) Elevator full up. (e) Rudder

------------------ 0.75 (e) Rudder 

### in neutral. (f) Rudder

------------------ 0.75 (f) Rudder at full throw.

• Apositive value ofK indicates a moment tending to depress the surface, while a negative value ofKindicates a moment tending to raise the surface. (d) The computed binge moment ofparagraph (b) must be used to determine the limit loads due to ground gust conditions for the control surface. A 1.25 factor onthe computed hinge moments must be used in calculating limit control system loads. (e) Where control system flexibility is such that the rate ofload application 

### in the ground gust conditions might produce transient stresses appreciably higherthan those corresponding to static loads, in the absence ofarational analysis an additional factor of 1.6 must be applied to the control system loads ofparagraph (d) to obtain limit loads. Ifa rational analysis is used, the additional factor must not be less than 1.20. (f) Forthe condition ofthe control locks engaged, the control surfaces, the control system locks and the parts ofthe control systems (ifany) between the surfaces and the locks must be designed to the respective resultant limit loads. Where control locks are not provided then the control surfaces, the control system stops nearest the surfaces, and the parts ofthe control systems (ifany) between the surfaces and the stops must be designed to the resultant limit loads. Ifthe control system design is such as to allow any part ofthe

21Rev 6
..20-01

control system to impact with the stops due to flexibility, then the resultant impact loads must be taken into account in deriving the limit loads due to ground gust. (g) Forthe condition oftaxiing with the control locks disengaged, the following apply: (1) The control surfaces, the control system stops nearest the surfaces and the parts ofthe control systems (ifany) betweenthe surfaces and the stops must be designed to the resultant limit loads. (2) The parts ofthe control systems betweenthe stops nearest the surfaces and the cockpit controls must be designed to the resultant limit loads, except that the parts of the control system where loads are eventually reacted by the pilot need not exceed: (i) The loads corresponding to the maximum pilot loads in §25.397 (c) for each pilot alone; or (ii) 0.75 times these maximum loads for each pilot when the pilot forces are applied inthe same direction.

Issued in on



## ------
Aircraft Certification Service

22Draft AC not for Public Distribution

U.S. Department ofTransportation Federal Aviation Administration GROUND GUST CONDITIONS 

# Advisory Circular

Date: 26September,2000 btitiated by: ANM-II0 AC No. 25.415-1 CItanp:

1. PURPOSE. This advisory circular (AC) sets forth acceptable methods ofcompliance with the provisions ofpart 25 ofthe Federal Aviation Regulations (FAR) dealing with the certification requirements for ground conditions. Guidance information is provided for showing compliance with § 25.415 ofthe FAR, relating to structural design ofthe control surfaces and systems while taxiing with control locks engaged and disengaged and when parked with control locks engaged. Other methods ofcompliance with the requirements may be acceptable. 2. RELATED FAR SECTIONS. The contents ofthis AC are considered by the Federal Aviation Administration (FAA) in determining compliance with § 25.415 ofthe FAR. 3. BACKGROUND.

a. The requirement to considerthe effects ofground gusts has been applied to transport airplane since 1950. The purpose ofthe requirement was to protectthe flight control system from excessive peak ground wind loads while the airplane is parked orwhile taxiing downwind. For developing the original regulation, the control surface load distribution was considered to be triangular with the peak at the trailing edge representing reversed flow overthe control surface. This assumption, along with assumptions about the wind approach angle and typical control surface geometries were developed into a table of hinge moment factors and set forth in the regulation. These hinge moment factors have been carried forward to the existing table in section § 25.415. The maximum design wind speed was originally set at 88 feet per second (52 knots) underthe presumption that higher speeds were predictable storm conditions and the aircraft owner could take additional precautions beyond engaging the standard gust locks. b. Amendment 25-91 incorporated a new condition into the FAR forjacking and tie down loads which was similarto the existing Joint Aviation Requirement 25.519. Those conditions required consideration ofthe airplane in a moored orjacked condition in wind speeds up to 65 knots. In orderto be consistent in the treatment ofground winds, § 25.415, concerning ground gust conditions on control surfaces, was increased to 65 knots at the same time.c. There have been several incidents and accidents caused by hidden damage that had previously occurred in ground gust conditions. Although many ofthese events were for airplanes that had used the lowerwind speeds from the earlierrules, analysis indicates that the most significant contributorto the damage was the dynamic load effect. The dynamic effects were most significant for control system designs in which the gust locks were designed to engage the control system at locations far from the control surface hom. Based on these events, Amendment 25-

## xx, in addition to clarifYing the rule, added additional factors for use inthose portions ofthe system and surface that could be affected by dynamic effects.

d. The flight control system and surface loads prescribedby section 25.415 are limit loads based on apeak wind speed of

### 6S knots EAS. Inoperation, the peakwind speed would most often be caused by an incremental fluctuation in velocity imposed ontop ofaless rapidly changing mean wind speed. Therefore, an appropriate peak wind speed limitation should be reflected inthe applicable documents, when there is a potential risk ofstructural damage.

4. COMPLIANCE.

a. The ground gust requirements take into account the conditions ofthe airplane parked with controls locked, and taxiing with controls eitherlocked orunlocked. Ineither ofthe locked conditions the control surface loads are assumed to be reacted at the control system locks. Inthe unlocked condition the pilot is assumed to be at the controls and the controls are assumed to be powered, ifapplicable. In the latter condition,Jhe control surface loads are assumed to be reacted, ifnecessary, at the cockpit controls bythe pilot(s) up to the limits ofthe maximum pilot forces and torques given in § 25.397(c). b. Where loads are eventually reacted at the cockpit controls, the loads in those parts of the control systembetween the control system stops nearest the control surfaces and the cockpit controls need not exceed those that would result from the application ofthe specified maximum pilot effort effects. However, higher loads canbe reacted by the control system stops. Those parts ofthe control systemfrom the control surfaces tothe control system stops nearest the surfaces should be designed to the resultant limit loads regardless ofpilot effort limitations. Similarly, pilot effort limitations would not apply to parts ofcontrol systems where the loads are not eventually reacted at the cockpit controls, for example an aileron control system where the right hand side aileron loads are reacted by the left hand side aileron, without participation by the pilot(s).
c. Ineitherthe taxiing condition (controls locked orunlocked) orthe parked condition (controls locked), ifthe control system flexibility is suchthat the rate ofload application inthe ground gust conditions might produce transient stresses appreciably higherthan those corresponding to static loads, the effects ofthis rate ofapplication are required to be considered. Manually powered control systems and control systems where the gust lockis located remotely from the control surface are examples ofdesigns that might fall inthis category. In such cases the control system loads are required by §25.41S(e) to be increasedby an additional factor overthe standard factor of1.25.**~~** 

# t:;; AIR LINE PILOTS ASSOCIATION, INTERNATIONAL 535 HERNDON PARKWAY 0 P.O. BOX 1169 0 HERNDON, VIRGINIA 20172-1169 0 703-689-2270 FAX 703-689-4370

Pratt & Whitney Attn: Craig R. Bolt MIS 162-24 400 Main Street East Hartford, CT 06108 July 9, 200 I

PW6000 ChiefSystems Engineer-Validation and Certification MIS 162-14 Dear Mr. Bolt: The Air Line Pilots Association, International (ALPA) does not concur with the Loads and Dynamics Harmonization Working Group (L&DHWG) report presented to TAEIG at the June 26-27,2001 meeting. We believe that operational considerations have not been appropriately included in determining certification standards. As noted in the report, ALPA previously commented that, for an aircraft with reversible flight controls, developing a design standard predicated on the assumption that pilots would physically restrain the controls during ground operation without a specific requirement to do so was not operationally realistic. The current HWG report has no provision to either fully account for reversible controls being unrestrained by the pilot(s) or a requirement that pilots be made aware ofthe design assumption that the controls would be restrained during ground operation. The report gives reasons for not making the provisions noted above, saying in part, "The L&DHWG does not feel that it is reasonable to operate an aircraft with manual control systems in design ground gust conditions with the pilot not constraining the control systems. This is supported by the FAA Flying Handbook FAA-H-8083-3 Chapter 2 for Ground Operations". This makes it clear that the certification standard relies on pilot actions to prevent control system damage. However, the proposed rule contains no provision that would ensure this design assumption becomes a part ofthe operational procedures for the airplane. In addition, we do not believe the citation ofFAA-H 8083-3 is valid. That handbook, the re-titled Advisory Circular 61-21, is intended for pilot training in general aviation aircraft. Although the basic principles of flight remain the same regardless ofaircraft size or intended use, the referenced document is clearly not intended to reflect the size, sophistication of systems, or the cockpit workload of multi-pilot aircraft in air carrier operations certified under Part 25. Some aircraft in air carrier service today (e.g. DC-9 series aircraft) have reversible controls that pilots are not able to keep from moving to the stops when blown by the wind. Irreversible control designs do not blow against the stops so pilot restraint is not required. Thus, most aircraft in airline service today are either reversible control designs in which pilot input is ineffective or irreversible control designs where pilot input is not required

- further basis for pilots not knowing they are required by a particular design to resist control movement or risk control system damage and perhaps failure.

SCHEDULE WITH SAFETY

....... " AFFILIATED WITH AFL·CIOALPA is concerned that this is an additional example ofinconsistency between a certification rule and operation ofthe aircraft. Ifthe rule is promulgated as proposed, we do not see how an FAA operations inspector can insure a specific carrier's aircraft operating procedure meets the needs ofcertification ifthe assumptions used in certification are not communicated to the inspector and the carrier. Thank you for the opportunity to comment. Sincerely,

# ~i!::::~ Director, Aircraft Certification**Program/~** JRB:ak

cc: J. Wallace