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 are 

contained 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 as 
agreed 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 differences 

identified 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). 

Schedule 
Within 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 Letter 
Pratt & 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 of this 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 of your 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, 

ORGINIAL SIGNED BY 

ANTHONY F. FAZIO 

Anthony F. Fazio 

Director, Office of Rulemaking 

ARM-209: E U pshaw:fs: 9/25/0 1 : PC DOCS #16015 

cc: ARM-1/20/200/209; APO-300/320, ANM-115/110 

File #ANM-00-552-A 

CONTROL NO. 20012470-0 
Recommendation 
Loads and Dynamics ARAC WG Report for 25.415 Ground Gust 

18 June 2001 

Harmonization (Category 3) and New Projects 

1- What is 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. However based 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 of control 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 draft NP A 25C-284 in response to 

this issue. 

The L&D HWG was assigned the task of harmonizing FAR and JAR 25.415 as a Fast 

Track Category 1 item. However the existence of the draft NP A 25C-284 and the safety 

issues addressed therein caused the L&D HWG to 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 - What are the current FAR and JAR standards relative to this subject? 

Current FAR text: 

(a) The control system must be designed as follows for control surface loads due 

to ground gusts and for taxiing downwind: 

(1) The control system between the stops nearest the surfaces and the cockpit 

controls must be designed for loads corresponding to the limit hinge 

moment of paragraph (a)(2) of this 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 of the system (if any) 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) of this 

section. 

c = mean chord of the control surface aft of the hinge line (ft); 

S = area of the control surface aft of the hinge line (sq ft); 

(b) The limit binge moment factor K for ground gusts must be derived as 

follows: 

Surface K Position of controls 

(a) Aileron --------------- 0.75 Control column locked or 

lashed in mid-p()sition. 

(b) Aileron ------------ *±O.50 Ailerons at full throw. 

(c) Elevator------------ *±O.75 (c) Elevator full down. 

(d) Elevator------------- *±O.75 (d) Elevator full up. 

(e) Rudder----------------- 0.75 (e) Rudder in neutral. 

(1) Rudder--------------- 0.75 (1) Rudder at full throw. 

* A positive value of K indicates a moment tending to depress the surface, while a negative 

value of K indicates a moment tending to raise the surface. 

Current JAR text (As of Change 15): 

Same as above FAR text. 

2a - H no FAR or JAR standard exists, what means have been used to ensure this 

safety issue is addressed? 

Not applicable. 

3 - What are the differences in the FAA and JAA standards or policy and what do 

these differences result in? 

There are no differences in current standards. It is however a JAA policy that for aircraft 

where the dynamic response of control systems may be significant for ground gusts, the 

dynamic effects of control systems be taken into account. The JAA requires consideration 

of the control systems "locked" while moored and ''unlocked'' when taxing downwind. 

4 - What, if any, are the differences in the current means of compliance? 

Discussed in item 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 for the 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 loads that can be produced by the pilot (or pitots) and by automatic or power 

devices operating the controls. 

(c) (retain current text) 

§ 25.415 Ground gust conditions. 

(a) The flight control systems and surfaces must be designed for the 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) of this paragraph 

Po = density of air at sea level = .0023769 (slugslfe) = .0023769 (I~Sec21 ft4) 

V = 65 knots = 109.71 fps relative to the aircraft 

S = area of the control surface aft of the hinge line (ft2) 

c = mean aerodynamic chord of the control surface aft of the 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) Elevator full down. 

(d) Elevator~-----------~- *:to.75 (d) Elevator full up. 

(e) Rudder----------- 0.75 (e) Rudder in neutral. 

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

* A positive value of K indicates a moment tending to depress the surface, while a negative 

value of K indicates 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 higher than 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. If a rational analysis is used, the 

additional factor must not be less than 1.20. 

(f) For the condition of the control locks engaged, the control surfaces, the control system locks 

and the parts of the 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 of the control 

systems (if any) between the surfaces and the stops must be designed to the resultant limit 

loads. If the control system design is such as to allow any part of the 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. 

(9) For the condition of taxiing 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 of the control systems between the 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 in 

the same direction. 

For each proposed change from the existing standard, answer the foUowing 

questions: 

6 - What should the harmonized standard be? 

See question 5. 

7 - Bow does 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 of factors 

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 current FAR, does the proposed standard increase, decrease, or 

maintain the same level of safety? Explain. 
Current level of safety is increased due to the elimination of confusing requirements and by 

requiring higher control system and control surface design loads requirements for ground 

gust where it is appropriate. 

9 - Relative to current industry practice, does the proposed standard increase, 

decrease, or maintain the same level of safety? Explain. 

Increases the level of safety. 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 of possible 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 a floor 

design level. 

10 - What other options have been considered and why were they not selected? 

The J AA has required that the dynamic effects be accounted for by analysis. Due to the 

difficulties in doing such analysis, the HWG believes that the proposed standard is more 

appropriate. 

The L&DHWG reviewed the issue of potential control system damage during aircraft 

ground operations in ground gust conditions. An issue had been raised regarding the 

potential for control system damage due to impact of the surfaces with the stop with the 

gust locks disengaged and with the control system not constrained by the pilot. 

The concern is for reversible systems such as manual systems that do not have a significant 

amount of damping. 

The following conclusions have been reached: 

1. The design load level has been increased by a factor of at least 2.5 relative to earlier 

design requirements for systems with significant flexibility. 

2. The proposed rule addresses the effect of control surface impact with the control stops 

for flexible systems. 

3. 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 F AA-H-8083-3 Chapter 

2 for Ground Operations. 

4. Some aircraft have operational procedures that require the gust lock to remain engaged 

until shortly before takeoff. 
5. The L&D HWG is not aware of conclusive evidence offailure of the control systems 

when the pilot is not constraining the flight controls. 

6. Therefore the L&DHWG believes that the requirements that have been developed for 

the instance where the pilot constrains the flight controls are adequate. 

7. The L&DHWG recommends that the TAEIG consider the need for additional 

operational procedures or the development of pilot informative material regarding the 

need for constraint of the 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 the rule text or preamble? 

A new ACJ is recommended based upon the draft AC per below. 

13 - Is existing FAA advisory material adequate? If not, what advisory material 

should be adopted? 

There is no existing FAA advisory material. A draft AC 25.415-1 , as attached, is 

proposed along with a corresponding ACI. 

14 - Bow does the proposed standard compare to the current ICAO standard? 

The current ICAO standard has no specific criteria for ground gust analysis. 

15 - Does the proposed standard affect other BWG's? 

No. 

16 - What is the cost impact of complying with the proposed standard? 

Economic analysis still to be done but it is expected to be small in comparison to standard 

industry practice. 

17. - If advisory or interpretive material is to be submitted, document the advisory 

or interpretive guidelines. If disagreement exists, document the disagreement. 

Draft Advisory Circular AC 25.415-1 is submitted. 
18 •• Does tbe HWG wisb to answer any supplementary questions specific to tbis 

project? 

Not at this time. 

19. - Does tbe HWG want to review tbe draft NPRM at "Pbase 4" prior to 

publication in tbe Federal Register? 

Yes 

20. -In ligbt of tbe information provided in tbis report, does tbe HWG consider 

tbat tbe "Fast Track" process is appropriate for tbis rulemaking project, or is tbe 

project too complex or controversial for tbe Fast Track Process? Explain. 

It is appropriate for the "Fast Track" process. 
D-R-A-F-T 

[4910-13] 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

(Docket No. ; Notice No. ] 

RIN: 2120-

Ground Gust Conditions. 

AGENCY: Federal Aviation Administration (FAA), DOT. 

ACTION: Notice of proposed 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 a result of the 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 a recommendation by the Aviation 

Rulemaking Advisory Committee (ARAC) and is intended to ensure that control systems 

and surfaces can withstand the ground gust conditions expected in service. The Joint 

Aviation Authorities (JAA) of Europe are considering a similar proposal to amend the 

Joint Aviation Requirements (JAR-25). Adopting this proposal would maintain similar 

requirements between the airworthiness standards of the U.S. and the Joint Aviation 

Requirements of Europe. 

DATES: Send your comments on or before [Insert date 60 days after date of publication 

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 of Transportation Dockets, Room Plaza 401,400 Seventh Street SW., 

Washington, DC 20590-0001. You must identify the docket number 

_______ at the beginning of your comments, and you should submit two 

copies of your comments. If you wish to receive confirmation that the FAA has received 

your comments, please include a self-addressed, stamped postcard on which the following 

statement is made: "Comments to Docket No. ." We will date-stamp the 

postcard and mail it back to 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 to this 

proposed regulation at the Department of Transportation Dockets Office, located on the 

plaza level of the Nassif Building 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. 

Information Docket: In addition, the FAA is maintaining an ''information docket" 

of comments 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. 

FOR FURTHER INFORMATION 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 in the making of the 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 identifY the regulatory docket 

number and be submitted in duplicate to the DOT Rules Docket address specified above. 

All comments received, as well as a report summarizing each substantive public 

contact with FAA personnel concerning this proposed rulemaking, will be filed in the 

docket. The docket is available for public inspection before and after the comment closing 

date. 

We will consider all comments received on or before the closing date before taking 

action on this proposed rulemaking. Comments filed late will be considered as far as 

possible without incurring expense or delay. The proposals in this document may be 

changed in light of the comments received. 

Bow Can I Obtain a Copy of this NPRM? 

You may download an electronic copy of this document using a modem and 

suitable communications software from the FAA regulations section of the Fedworld 

electronic bulletin board service (telephone: 703-321-3339); the Government Printing 

Office (GPoys electronic bulletin board 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 or the GPO's web page at 

http://www.access.gpo.gov/nara. 

3 
D-R-A-F-T Rev 6-20-01 

Any person may obtain a copy of this document by submitting a request to the 

Federal Aviation Administration, Office of Rule making, ARM-I, and 800 Independence 

Avenue, SW., Washington, DC 20591; or by calling 202- 267-9680. Communications 

must identify the docket number of this NPRM. 

Any person interested in being placed on the mailing list for future rulemaking 

documents should request from the above office a copy of Advisory Circular 11-2A, 

''Notice of Proposed Rulemaking Distribution System," which describes the application 

procedure. 

What Are the Relevant Airworthiness Standards in the United States? 

In the United States, the airworthiness standards for type certification of transport 

category airplanes are contained in 14 Code of Federal 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 of a 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 to the U.S. under a 

bilateral airworthiness agreement. 

What Are the Relevant Airworthiness Standards in Europe? 

In Europe, the airworthiness standards for type certification of transport 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) of Europe to provide a 

common set of airworthiness 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. 

4 
D-R-A-F-T Rev 6-20-01 

What is "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 of standards, 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 of both sets of standards, although the level of safety is not 

increased correspondingly. 

Recognizing that a common set of standards would not only benefit the aviation 

industry economically, but also maintain the necessary high level of safety, the FAA and 

the JAA began an effort in 1988 to "harmonize" their respective aviation standards. The 

goal of the harmonization effort is to ensure that: 

• where possible, standards do not require domestic and foreign parties to manufacture 

or operate to 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" of the two sets of standards 

a high priority. 

What is ARAC and What Role Does it Play in Harmonization? 

After initiating the first steps towards harmonization, the FAA and JAA soon 

realized that traditional methods of rulemaking and accommodating different 

administrative procedures was neither sufficient nor adequate to make appreciable 

progress towards fulfilling the goal of harmonization. The FAA then 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 FAA tasked ARAC to undertake the 

entire harmonization effort. 

The FAA had fonnally established ARAC in 1991 (56 FR 2190, January 22, 1991), 

to provide advice and recommendations concerning the full range of the FAA's safetyrelated rulemaking activity. The FAA sought this advice to develop better rules in less 

overall time and using fewer FAA resources than previously needed. The committee 

provides the FAA firsthand infonnation and insight from interested parties regarding 

potential new rules or revisions of existing rules. 

There are 64 member organizations on the committee, representing a wide range 

of interests within the aviation community. Meetings of the committee are open to the 

public, except as authorized by section 10(d) of the Federal Advisory Committee Act. 

The ARAC establishes working groups to develop recommendations for resolving 

specific airworthiness issues. Tasks assigned to working groups are published in the 

F edetal Register. Although working group meetings are not generally open to the public, 

the FAA solicits participation in working groups from interested members of the 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 of the ARAC will not, however, circumvent the public ruIemaking 

procedures; nor is the FAA limited to the rule language "recommended" by ARAC. If the 

FAA accepts an ARAC recommendation, the agency proceeds with the normal public 

rulemaking procedures. Any ARAC participation in a rulemaking package is fully 

disclosed in the public docket. 

What is the Status of the Harmonization Effort Today? 

Despite the work that ARAC has undertaken to address harmonization, there 

remain a large number of regulatory differences between part 25 and JAR-2S. The current 

6 
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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 their resources and to finally establish one 

acceptable set of standards. 

Recently, representatives of the aviation industry [including Aerospace Industries 

Association of America, Inc. (AlA), General Aviation Manufacturers Association 

(GAMA), and European Association of Aerospace 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 standards by 

accepting the more "stringent" of the two standards. "Stringent," in this case, indicates 

the relative higher level of safety, or greater applicability to modem technology, between a 

part 25 standard and the parallel JAR-25 standard. 

Aviation industry groups further refined their proposed process by suggesting that 

the 42 part 25 standards that have already been tasked to ARAC for harmonization be 

divided into three categories: 

Category 1: Envelope - For these standards, parallel part 25 and JAR-25 

standards would be compared, and harmonization would be reached by accepting the more 

stringent of the two standards. In some cases, it may be necessary to incorporate parts of 

both the 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 of the other.). 

Category 2: Completed or near complete - For these standards, ARAC has 

reached, or has nearly reached, technical agreement or consensus on the new wording of 

the proposed harmonized standards. 

Category 3: Harmonize - For these standards, ARAC is not near technical 

agreement on harmonization, and the parallel part 25 and JAR-25 standards cannot be 

7 
- ---- -~ ~ ~-------------L-___ -.-J 

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

"enveloped" (as described under Category 1) for reasons of safety or unacceptability. A 

standard developed under Category 3 would be mutually acceptable to the FAA and JAA, 

with a consistent means of compliance. 

What is the "Fast Track Harmonization Program"? 

In light of the general agreement among the affected industries and authorities to 

expedite the harmonization program, and a willingness to consider «enveloping" of parallel 

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 FAA initiated the Fast Track program on November 26, 1999 (64 FR 66522), 

by re-tasking ARAC to accomplish the following: 

• Review a list of part 25/JAR~25 standards (approximately 120 parallel 

pairs) identified by industry, FAA, and JAA as having differences that 

should be harmonized in order to establish one single set of standards that 

represent the highest level of safety. 

• Identity changes necessary to the standards to harmonize part 25 and JAR~ 

25. 

• Submit to the FAA a technical report on each standard and recommend 

what the requirements of the harmonized standard should be. 

The FAA then considers the recommendations submitted by ARAC and initiates 

rulemaking action, as appropriate, based on those recommendations. 

As implemented, the Fast Track program achieves its aims by: 

• considering the fundamentals of the industry proposals, 

• defining a process for expeditiously adopting the harmonized requirements, 

8 
D·R .. A-F· T Rev 6-20-01 

• 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 OF THE PROPOSAL 

How Does This Proposed Regulation Relate to "Fast Track"? 

This proposed regulation results from the recommendations of ARAC submitted 

under the FAA's Fast Track Harmonization 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 a result of some near accidents in Europe 

and they have been in the process of preparing a notice of proposed 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 of the fast track program (category 3) in order to 

ensure a harmonized proposal would be achieved to address the safety concerns. In this 

notice, the FAA proposes to amend § 25.415, concerning ground gust conditions. The 

JAA plans a similar revision to the JAR. 

What is 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 to prevent damage to the control system that 

may not be detected before take-off 

The current airworthiness standards contained in 14 CFR part 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 (if applicable) engaged, and the other, a taxi condition with the gust locks 

disengaged with the controls system powered (if applicable) and/or restrained by the pilot. 

The requirement to consider the effects of ground gusts has been applied to 

transport airplane since 1950. The purpose of the 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 triangular with the peak at the trailing edge representing reversed 

flow over the 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 § 25.415. The maximum 

design wind speed was originally set at a maximum of88 feet per second (52 knots) 

under the 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 

for jacking and tie down loads which was similar to the existing Joint Aviation 

Requirement in paragraph 25.519. Those conditions required consideration of the 

airplane in a moored or jacked condition in peak wind speeds up to 65 knots. In order 

to be consistent in the treatment of ground winds, section 25.415, concerning ground 

gust conditions on control surfaces, was increased to 65 knots. 

10 
D-R-A .. F-T Rev 6-20-01 

What are the Current JAR-25 and 14 CFR Standards? 

The current texts 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 system between 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) of this 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 in the same direction. 

(2) The control system stops nearest the surfaces, the control system locks, and 

the parts of the systems (if any) 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 == .0034KV2cS, where_ 

V := 65 (wind speed in knots) 

K = limit hinge moment factor for ground gusts derived in paragraph (b) of this 

section. 

c:= mean chord of the control surface aft ofthe hinge line (ft)~ 

S := area of the control surface aft of the 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 of controls 

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. 

* A positive value of K indicates a moment tending to depress the surface, while a 

negative value of K indicates a moment tending to raise the surface. 

How Have the Standards Been Applied? 

Most of the experience in complying with the requirement are for airplanes with 

certification bases prior to amendment 25-91 (or JAR Change 15) so they were required 

to be designs to a speed of 52 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 in the control system between the 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, or control system power, or both. Section 25.391 "Control 

System Loads", requires an additional mUltiplying factor of 1.25 on the control system 

loads due to the control surface aerodynamic binge moments but this 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 protect the 

airplane against all possible ground wind conditions that may occur. Wind conditions with 

12 
O-R-A-F-T Rev 6-20-01 

gusts in excess of the original design speed of 52 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 on jacks. 

Several incidents that have occurred to aircraft on the United Kingdom register 

and at least one aircraft on the US register where the aircraft sustained severe ground gust 

damage to the flight control system which went undetected until after takeoff. These 

incidents occurred on airplanes with unpowered mechanical controls with significant 

flexibility between the contol surface and the gust locking devices. This flexibility allows 

dynamic loads, well in excess of the 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 clarification to 

ensure the application of the 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 

suscepttble to dynamic load amplification because of the control system and gust lock 

configuration. 

What Is the Proposed Action and How Does It Address 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 a taxiing case with the gust locks disengaged but 

13 
O-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 of the control system. 

A further multiplying factor of 1.6 (total multiplying factor of2.0) would be applied for 

those parts of the 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 of the 1.25 

factor) over the past practices could be on the order of a 95 percent increase in the static 

ground gust design loads for the control system. For those parts of the control systems 

where dynamic amplification is of concern a total load increase of over 200 percent in the 

required design load may be realized along with a coresponding increase in strength. 

These load levels should be sufficient to account for the expected ground gust loads that 

are likely to occur in 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 of their 

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 of 1.6 would be required for 

parts of the control system where dynamic effects are expected to be significant. The rule 

would be organized to clarifY the cases to be considered and to identifY the components 

and parts of the control system and surface to which each of the conditions apply. 

The JAA plans parallel changes to JAR-2S. 

14 
Rev 6-20-01 

Is Existing FAA Advisory Material Adequate? 

The FAA is preparing to issue a new proposed Advisory Circular 25.415-1, 

"Ground gust conditions," to describe a means of compliance with the proposed 

regulation, which would meet the intended level of safety and promote consistent and 

effective application of the proposed revised standards. Public comments concerning the 

proposed AC are invited by separate notice published elsewhere in this issue of the Federal 

Register 

REGULATORY ANALYSES AND ASSESSMENTS 

Paperwork Reduction Act 

In accordance with the Paperwork Reduction Act of 1995 [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 under the Convention on International Civil 

Aviation, it is FAA policy 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 Practices that 

correspond to this proposed regulation. 

Regulatory Evaluation Summary 

Changes to Federal regulations must undergo several economic analyses. First, 

Executive Order 12866 directs 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 requires agencies to 

analyze the economic effect of regulatory changes on small entities. Third, the Office of 

Management and Budget directs agencies to assess the effects of regulatory changes on 

international trade. And fourth, the Unfunded Mandates Reform Act of 1995 (Pub. L. 

15 
O-R-A-F-T Rev 6-20-01 

104-4) requires agencies to prepare a written assessment of the cots, 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). 

In conducting these analyses, the FAA has determined that this proposed rule: (1) 

would generate benefits that justify its costs and would not be "a significant regulatory 

action" as defined in section 3(f) of Executive Order 12866 and, therefore, is not subject 

to review by the Office of Management and Budget; (2) would not have a significant 

impact on a substantial number of small entities; (3) would not constitute a barrier to 

international trade; and (4) would not contain a significant intergovernmental or private 

sector mandate. These analyses, available in the docket, are summarized below. 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 of 1980 (RF A) establishes "as a principle of 

regulatory issuance that agencies shall endeavor, consistent with the objective of the rule 

and of applicable statutes, to fit regulatory and informational requirements to the scale of 

the business, organizations, and governmental jurisdictions subject to regulation." To 

achieve that principle, the Act requires agencies to solicit and consider flexible regulatory 

proposals and to explain the rationale for their actions. The Act covers a wide-range of 

small entities, including small businesses, not-for-profit organizations, and small 

governmental jurisdictions. 

Agencies must perform a review to determine whether a proposed rule will have a 

significant economic impact on a substantial number of small entities. If the determination 

16 
O-R-A-F-T Rev 6-20-01 

is that it will, the agency must prepare a regulatory flexibility analysis as descnbed in the 

Act. 

However, if an agency determines that a proposed or final rule is not expected to 

have a significant economic impact on a substantial number of small entities, section 

605(b) of the 1980 Act 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. 

[APO to add economic evaluation here. J 

International Trade Impact Assessment 

The provisions of this proposed rule would have little or no impact on trade 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 on the 

States, on the relationship between the national Government and the states, or on the 

distribution of power and responsibilities among the various levels of government. 

Therefore, in accordance with Executive Order 12612, it is determined that this proposal 

would not have sufficient federalism implications to warrant the preparation of a 

federalism assessment. 

Unfunded Mandates Reform Act 

Title IT of the Unfunded Mandates Reform Act of 1995 (the Act), codified in 

2 U.S.C. 1501-1571, requires each Federal agency, to the extent permitted by law, to 

prepare a written assessment of the effects of any Federal mandate in a proposed or final 

agency rule that may result in the expenditure by State, local, and tribal governments, in 

the aggregate, or by the private sector, of$100 million or more (adjusted annually for 

inflation) in anyone year. Section 204(a) of the Act, 2 U.S.C. 1534(a), requires the 

17 
D-R .. A-F-T Rev 6 .. 20-01 

Federal agency to develop an effective process to permit timely input by elected officers 

(or their designees) of State, local, and tribal governments on a proposed "significant 

intergovernmental mandate." A "significant intergovernmental mandate" under the Act is 

any provision in a Federal 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 anyone year. Section 203 of the Act, 2 U.S.C. 1533, which supplements 

section 204(a), provides that before establishing any regulatory requirements that might 

significantly or uniquely affect small governments, the agency shall have developed a plan 

that, among other things, 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 a Federal intergovernmental or private sector 

mandate that exceeds $100 million in anyone year. 

Environmental Analysis 

FAA Order 1050.1D defines FAA actions that may be categorically excluded from 

preparation of a National 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 of the 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). It has been determined that it is not a major regulatory action under the 

provisions of the EPCA. 

18 
D .. R-A-F-T Rev 6 .. 20-01 

Regulations Affecting Intrastate Aviation in Alaska 

Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat. 3213) requires 

the Administrator, when modifying regulations in Title 14 of the CFR 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 such regulatory distinctions 

as he or she considers appropriate. Because this proposed rule would apply to the 

certification of future designs of transport category airplanes and their subsequent 

operation, it could, if adopted, affect intrastate aviation in Alaska. The FAA therefore 

specifically requests comments on whether there is justification for applying the proposed 

rule differently to intrastate operations in Alaska. 

List of Subjects in 14 CFR Part 25: 

Aircraft, Aviation safety, Reporting and record keeping requirements 

The Proposed Amendment 

In consideration of the foregoing, the Federal Aviation Administration proposes to 

amend part 25 of Title 14, Code of Federal Regulations, as follows: 

Part 25 .. 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 by removing the reference to § 25.415 as follows: 

§ 25.391 Control surface loads: 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 to hinge line, in § 25.393; 

(b) Pilot effort effects, in § 25.397; 

19 
-------~--~~~----~~-

---------------------~------------j 

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

(c) Trim tab 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 of paragraph (a) of § 25.395. 

§ 25.395 Control System 

* * * 

(b) The system limit loads of paragraph (a) need not exceed the loads that can be 

produced by the pilot ( or pilots) and by automatic or power 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 the 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 binge moments H, in foot pounds, must be computed from the formula, 

H=K 1I2po V fps2cS 

where: 

K = binge moment factor for ground gusts derived in paragraph ( c) of this paragraph 

po = density of air at sea level = .0023769 (slugS/fl?) = .0023769 (Ib~sec2/ ft4) 

V = 65 knots = 109.71 fps relative to the aircraft 

S = area of the control surface aft of the hinge line (fl?) 

c = mean aerodynamic chord of the control surface aft of the 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 of controls 

(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. 

• A positive value of K indicates a moment tending to depress the surface, while a 

negative value of K indicates a moment tending to raise the surface. 

(d) The computed binge 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 higher than 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. If a 

rational analysis is used, the additional factor must not be less than 1.20. 

(f) For the condition of the control locks engaged, the control surfaces, the control 

system locks and the parts of the 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 of the control systems (if any) between the surfaces and the stops must be designed 

to the resultant limit loads. If the control system design is such as to allow any part of the 

21 
Rev 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) For the condition of taxiing 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 of the control systems between the 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 in the same direction. 

Issued in on ------

Aircraft Certification Service 

22 
Draft AC not for Public Distribution 

U.S. Department 

of Transportation 

Federal Aviation 

Administration 

GROUND GUST CONDITIONS 

Advisory 

Circular 

Date: 26 September, 2000 

btitiated by: ANM-II0 

AC No. 25.415-1 

CItanp: 

1. PURPOSE. This advisory circular (AC) sets forth acceptable methods of compliance 

with the provisions of part 25 of the Federal Aviation Regulations (FAR) dealing with the 

certification requirements for ground conditions. Guidance information is provided for 

showing compliance with § 25.415 of the FAR, relating to structural design of the control 

surfaces and systems while taxiing with control locks engaged and disengaged and when 

parked with control locks engaged. Other methods of compliance with the requirements may 

be acceptable. 

2. RELATED FAR SECTIONS. The contents of this AC are considered by the Federal 

Aviation Administration (FAA) in determining compliance with § 25.415 of the FAR. 

3. BACKGROUND. 

a. The requirement to consider the effects of ground gusts has been applied to 

transport airplane since 1950. The purpose of the requirement was to protect the flight 

control system from excessive peak ground wind loads while the airplane is parked or while 

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 over the 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) under the 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 for jacking and tie 

down loads which was similar to the existing Joint Aviation Requirement 25.519. Those 

conditions required consideration of the airplane in a moored or jacked condition in wind 

speeds up to 65 knots. In order to be consistent in the treatment of ground 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 of these events were for 

airplanes that had used the lower wind speeds from the earlier rules, analysis indicates that 

the most significant contributor to 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 in those portions of the system and surface that could be affected by dynamic 

effects. 

d. The flight control system and surface loads prescribed by section 25.415 are limit loads 

based on a peak wind speed of 6S knots EAS. In operation, the peak wind speed would most 

often be caused by an incremental fluctuation in velocity imposed on top of a less rapidly 

changing mean wind speed. Therefore, an appropriate peak wind speed limitation should be 

reflected in the applicable documents, when there is a potential risk of structural damage. 

4. COMPLIANCE. 

a. The ground gust requirements take into account the conditions of the airplane parked 

with controls locked, and taxiing with controls either locked or unlocked. In either of the locked 

conditions the control surface loads are assumed to be reacted at the control system locks. In the 

unlocked condition the pilot is assumed to be at the controls and the controls are assumed to be 

powered, if applicable. In the latter condition,Jhe control surface loads are assumed to be 

reacted, ifnecessary, at the cockpit controls by the pilot(s) up to the limits of the 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 system between the control system stops nearest the control surfaces and the cockpit 

controls need not exceed those that would result from the application of the specified maximum 

pilot effort effects. However, higher loads can be reacted by the control system stops. Those 

parts of the control system from the control surfaces to the control system stops nearest the 

surfaces should be designed to the resultant limit loads regardless of pilot effort limitations. 

Similarly, pilot effort limitations would not apply to parts of control 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. In either the taxiing condition (controls locked or unlocked) or the parked condition 

(controls locked), if the control system flexibility is such that the rate of load application in the 

ground gust conditions might produce transient stresses appreciably higher than those 

corresponding to static loads, the effects of this rate of application are required to be considered. 

Manually powered control systems and control systems where the gust lock is located remotely 

from the control surface are examples of designs that might fall in this category. In such cases the 

control system loads are required by § 25. 41S( e) to be increased by an additional factor over the 

standard factor of 1.25. 
~~ 

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 Chief Systems 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 of the 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 of the operational procedures for the airplane. In addition, we do not 

believe the citation of FAA-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 of aircraft 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·CIO 
ALP A is concerned that this is an additional example of inconsistency between a certification 

rule and operation of the aircraft. If the 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 of certification if the 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