Federal Register / Vol. 78, No. 102 / Tuesday, May 28, 2013 / Proposed Rules 31851 

Executive order, including E.O. 12968, 

as amended, and the agency’s own 

procedural regulations, and must: 

(a) Ensure that the records used in 

making the decision are accurate, 

relevant, timely, and complete to the 

extent reasonably necessary to assure 

fairness to the individual in any 

determination; 

(b) Consider all available, relevant 

information in reaching its final 

decision; and 

(c) At a minimum, subject to 

requirements of law, rule, regulation, or 

Executive order: 

(1) Provide the individual concerned 

notice of the specific reason(s) for the 

decision, an opportunity to respond, 

and notice of appeal rights, if any; and 

(2) Keep any record of the agency 

action required by OPM as published in 

its issuances. 

§ 1400.302 Reporting to OPM. 

(a) Each agency conducting an 

investigation under E.O. 10450 is 

required to notify OPM when the 

investigation is initiated and when it is 

completed. 

(b) Agencies must report to OPM an 

adjudicative determination and action 

taken with respect to an individual 

investigated pursuant to E.O. 10450 as 

soon as possible and in no event later 

than 90 days after receipt of the final 

report of investigation. 

(c) To comply with process efficiency 

requirements, additional data may be 

collected from agencies conducting 

investigations or taking action under 

this part. These collections will be 

identified in separate OPM guidance, 

issued as necessary under 5 CFR 

732.103. 

[FR Doc. 2013–12556 Filed 5–23–13; 11:15 am] 

BILLING CODE 6325–39–P; 3910–A7–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No.: FAA–2013–0142; Notice No. 

25–139] 

RIN 2120–AK12 

Harmonization of Airworthiness 

Standards—Gust and Maneuver Load 

Requirements 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of proposed rulemaking 

(NPRM). 

SUMMARY: The FAA proposes to amend 

certain airworthiness regulations for 

transport category airplanes based on 

recommendations from the Aviation 

Rulemaking Advisory Committee 

(ARAC). Adopting this proposal would 

eliminate certain regulatory differences 

between the airworthiness standards of 

the FAA and European Aviation Safety 

Agency (EASA) without affecting 

current industry design practices. This 

action would revise the pitch maneuver 

design loads criteria; revise the gust and 

turbulence design loads criteria; revise 

the application of gust loads to engine 

mounts, high lift devices, and other 

control surfaces; add a ‘‘round-theclock’’ discrete gust criterion and a 

multi-axis discrete gust criterion for 

airplanes equipped with wing-mounted 

engines; revise the engine torque loads 

criteria; add an engine failure dynamic 

load condition; revise the ground gust 

design loads criteria; revise the criteria 

used to establish the rough air design 

speed, and require the establishment of 

a rough air Mach number. 

DATES: Send comments on or before 

August 26, 2013. 

ADDRESSES: Send comments identified 

by docket number FAA–2013–0142 

using any of the following methods: 

• Federal eRulemaking Portal: Go to 

http://www.regulations.gov and follow 

the online instructions for sending your 

comments electronically. 

• Mail: Send comments to Docket 

Operations, M–30; U.S. Department of 

Transportation (DOT), 1200 New Jersey 

Avenue SE., Room W12–140, West 

Building Ground Floor, Washington, DC 

20590–0001. 

• Hand Delivery or Courier: Take 

comments to Docket Operations in 

Room W12–140 of the West Building 

Ground Floor at 1200 New Jersey 

Avenue SE., Washington, DC, between 9 

a.m. and 5 p.m., Monday through 

Friday, except Federal holidays. 

• Fax: Fax comments to Docket 

Operations at (202) 493–2251. 

For more information on the 

rulemaking process, see the 

SUPPLEMENTARY INFORMATION section of 

this document. 

Privacy: The FAA will post all 

comments it receives, without change, 

to http://www.regulations.gov, including 

any personal information the 

commenter provides. Using the search 

function of the docket Web site, anyone 

can find and read the electronic form of 

all comments received into any FAA 

dockets, including the name of the 

individual sending the comment (or 

signing the comment for an association, 

business, labor union, etc.). DOT’s 

complete Privacy Act Statement can be 

found in the Federal Register published 

on April 11, 2000 (65 FR 19477–19478), 

as well as at http://DocketsInfo.dot.gov. 

Docket: Background documents or 

comments received may be read at 

http://www.regulations.gov at any time. 

Follow the online instructions for 

accessing the docket or go to the Docket 

Operations in Room W12–140 of the 

West Building Ground Floor at 1200 

New Jersey Avenue SE., Washington, 

DC, between 9 a.m. and 5 p.m., Monday 

through Friday, except Federal holidays. 

FOR FURTHER INFORMATION CONTACT: For 

technical questions concerning this 

action, contact Todd Martin, Airframe 

and Cabin Safety Branch, ANM–115, 

Transport Airplane Directorate, Aircraft 

Certification Service, Federal Aviation 

Administration, 1601 Lind Avenue SW., 

Renton, WA 98057–3356; telephone 

(425) 227–1178; facsimile (425) 227– 

1232; email Todd.Martin@faa.gov. 

For legal questions concerning this 

action, contact Sean Howe, Office of the 

Regional Counsel, ANM–7, Federal 

Aviation Administration, 1601 Lind 

Avenue SW., Renton, Washington 

98057–3356; telephone (425) 227–2591; 

facsimile (425) 227–1007; email 

Sean.Howe@faa.gov. 

SUPPLEMENTARY INFORMATION: 

Authority for This Rulemaking 

The FAA’s authority to issue rules on 

aviation safety is found in Title 49 of the 

United States Code. Subtitle I, Section 

106 describes the authority of the FAA 

Administrator. Subtitle VII, Aviation 

Programs, describes in more detail the 

scope of the agency’s authority. 

This rulemaking is promulgated 

under the authority described in 

Subtitle VII, Part A, Subpart III, Section 

44701, ‘‘General Requirements.’’ Under 

that section, the FAA is charged with 

promoting safe flight of civil aircraft in 

air commerce by prescribing regulations 

and minimum standards for the design 

and performance of aircraft that the 

Administrator finds necessary for safety 

in air commerce. This regulation is 

within the scope of that authority. It 

prescribes new safety standards for the 

design and operation of transport 

category airplanes. 

I. Overview of Proposed Rule 

The FAA proposes to amend the 

airworthiness regulations described 

below. This action would harmonize 

Title 14, Code of Federal Regulations 

(14 CFR) part 25 requirements with the 

corresponding requirements in Book 1 

of EASA Certification Specifications 

and Acceptable Means of Compliance 

for Large Aeroplanes (CS–25). 

The following proposals result from 

ARAC recommendations made to the 

FAA and EASA: 

1. Amend § 25.331, ‘‘Symmetric 

maneuvering conditions;’’ 


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2. Amend § 25.341, ‘‘Gust and 

turbulence loads;’’ 

3. Amend § 25.343, ‘‘Design fuel and 

oil loads;’’ 

4. Amend § 25.345, ‘‘High lift 

devices;’’ 

5. Amend § 25.361, ‘‘Engine torque;’’ 

6. Add § 25.362, ‘‘Engine failure 

loads;’’ 

7. Amend § 25.371, ‘‘Gyroscopic 

loads;’’ 

8. Amend § 25.373, ‘‘Speed control 

devices;’’ 

9. Amend § 25.391, ‘‘Control surface 

loads: General;’’ 

10. Amend § 25.395, ‘‘Control 

system;’’ 

11. Amend § 25.415, ‘‘Ground gust 

conditions;’’ 

12. Amend § 25.1517, ‘‘Rough air 

speed, VRA;’’ 

13. Remove appendix G, ‘‘Continuous 

Gust Design Criteria.’’ 

II. Background 

Part 25 prescribes airworthiness 

standards for type certification of 

transport category airplanes for products 

certified in the United States. EASA CS– 

25 Book 1 prescribes the corresponding 

airworthiness standards for products 

certified in Europe. While part 25 and 

CS–25 Book 1 are similar, they differ in 

several respects. To improve 

certification efficiency, the FAA tasked 

ARAC through the Loads and Dynamics 

Harmonization Working Group 

(LDHWG) to review existing structures 

regulations and recommend changes 

that would eliminate differences 

between the U.S. and European 

airworthiness standards, while 

maintaining or improving the level of 

safety in the current regulations. 

All of the proposals below are based 

on LDHWG recommendations, which 

EASA has already incorporated into CS– 

25 Book 1. The FAA agrees with the 

ARAC recommendations as adopted by 

EASA, and we propose to amend part 25 

accordingly. The proposals are not 

expected to be controversial and should 

reduce certification costs to industry 

without adversely affecting safety. The 

complete analyses for the proposed 

changes made in response to ARAC 

recommendations can be found in the 

ARAC recommendation reports, located 

in the docket for this rulemaking. 

Note: In most cases, the language and 

diagrams in this proposed rule are similar to 

related rules found in CS–25, Book 1 with 

one exception: The FAA uses the term ‘‘flight 

deck’’ where EASA uses the term ‘‘cockpit.’’ 

The meaning and intent of these terms are 

the same. 

III. Discussion of the Proposal 

A. Revise ‘‘Symmetric Maneuvering 

Conditions’’ (§ 25.331) 

Section 25.331(c)(2) currently 

prescribes a checked pitching maneuver 

(a design load condition) in which the 

flight deck pitch control is first 

displaced in a nose-up direction, then 

the control is displaced in the opposite 

direction sufficient to ‘‘check’’ the 

pitching motion. The control 

displacements must develop specified 

nose-up and nose-down pitching 

accelerations. The pitching 

accelerations prescribed in the current 

regulations do not account for the size, 

configuration, or characteristics of the 

airplane. Also, the current regulations 

do not fully account for the 

characteristics of advanced electronic 

flight control systems in which the 

achievable maneuvering load factors are 

governed by computer control laws. 

We propose to revise § 25.331(c)(2) 

based on the recommendation from the 

LDHWG. The proposed requirement 

would prescribe both positive and 

negative checked pitch maneuver loads 

that take into account the size of the 

airplane and any effects of the flight 

control system. We would also revise 

the introductory paragraph, § 25.331(c), 

by moving some criteria to § 25.331(c)(2) 

where those criteria apply. 

The LDHWG recommended a checked 

pitching maneuver requirement that was 

based on the corresponding requirement 

in the former Joint Aviation Regulations 

(JAR) but with some modifications to 

account for advanced flight control 

systems. The proposal specifies a 

control input in the form of a sine wave 

as a baseline control motion. This 

control motion is applied with the 

initial movement in the nose-up 

direction so that the maximum positive 

limit maneuvering load factor is 

achieved. As a separate condition, the 

control motion is applied with the 

initial movement in the nose-down 

direction, so that a maneuvering load 

factor of 0g is reached. In both cases, the 

control motion is applied at a frequency 

related to the short-period rigid body 

mode of the airplane. The short-period 

rigid body mode is one of the two 

longitudinal stability modes that are 

inherent in every airplane and 

identified during the design phase. 

In cases where the load factors are not 

achievable with a simple sine wave 

using amplitude that fits within the 

limits of the control stops or the pilot 

effort limits, a modified sine wave 

within these limits is required with a 

dwell at the maximum control 

displacement. The time delay is varied 

to the extent necessary to achieve the 

specified load factors up to a maximum 

time beyond which the maneuver would 

no longer be considered rational. 

These actions would harmonize 

§ 25.331 with the corresponding EASA 

standards. 

B. Revise ‘‘Gust and Turbulence Loads’’ 

(§ 25.341) and ‘‘Continuous Gust Design 

Criteria’’ (Appendix G to Part 25) 

Section 25.341 requires that the 

airplane be designed for gust and 

turbulence loads. These loads are 

currently specified in § 25.341(a) 

Discrete Gust Design Criteria 

(representing a singular gust), and 

§ 25.341(b) Continuous Gust Design 

Criteria (representing continuous 

turbulence). Section 25.341(b) 

references the continuous gust criteria 

specified in appendix G of part 25 and 

requires that these criteria be used for 

the evaluation of continuous turbulence. 

We propose to: 

1. Remove appendix G and specify the 

continuous turbulence requirement 

directly in § 25.341(b); and remove the 

optional mission analysis method 

currently specified in appendix G in 

favor of the design envelope analysis 

method. 

The elimination of the optional 

mission analysis method would not be 

significant since few manufacturers 

currently use it as the primary means of 

addressing continuous turbulence. The 

LDHWG determined that predicting the 

mission is not always reliable since 

missions can change after the airplane 

goes into operation. Furthermore, the 

mission analysis design loads are 

sensitive to small changes in the 

definition of the aircraft mission. 

Therefore, small variations in approach 

can provide inconsistent results. The 

elimination of the mission analysis 

method leaves only the design envelope 

analysis method. 

2. Revise the turbulence intensity 

criteria in § 25.341(b) to take into 

account in-service measurements of 

derived gust intensities. 

The FAA and other organizations 

have endeavored to better define the 

atmospheric model to be used for gust 

and turbulence loads. The Civil 

Aviation Authority (CAA) of the United 

Kingdom conducted a comprehensive 

gust measurement program for transport 

airplanes in airline service. The 

program, called Civil Aircraft 

Airworthiness Data Recording Program 

(CAADRP), resulted in an extensive 

collection of reliable gust data that 

provided an improved insight into the 

distribution of gusts in the atmosphere. 

The FAA already revised § 25.341(a) 

(Amendment 25–86, 61 FR 5218, dated 

February 9, 1996) to provide a revised 


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discrete gust methodology along with a 

refined gust distribution model of the 

atmosphere based on the CAADRP data. 

The FAA proposes to retain the design 

envelope criterion and prescribe the 

gust intensity distribution based on the 

CAADRP data. In addition, the flight 

profile alleviation factor already defined 

for the discrete gust in § 25.341(a) 

would be used to adjust the gust 

intensity distribution according to 

certain aircraft parameters that relate to 

the intended use of the airplane. The 

FAA considers this to be a reliable and 

uniform means of accounting for 

airplane mission. 

The introduction of advanced flight 

control systems into transport airplanes 

has presented special problems in the 

treatment of continuous turbulence. 

Some of these systems can exhibit 

significant non-linearities, while the 

standard mathematical approaches to 

continuous turbulence (i.e., frequency 

domain solutions) are valid only for 

linear systems. The proposed rule 

would require that any significant nonlinearity be considered in a realistic or 

conservative manner. 

3. Revise § 25.341(a) to require 

evaluation of discrete gust conditions at 

airplane speeds from VB to design 

cruising speed, VC, (currently required 

only at VC) and to expand the definition 

of gust speeds up to 60,000 feet 

(currently defined up to 50,000 feet). 

The change to the discrete gust 

criteria is necessary to ensure airplanes 

are designed to withstand gust loads at 

lower speeds and is consistent with the 

proposed continuous turbulence 

criteria. 

Some current part 25 airplanes have 

maximum certified operating altitudes 

up to 51,000 feet. To be fully applicable 

to these and future part 25 airplanes, 

this proposal defines gust intensities for 

altitudes up to 60,000 feet. Currently, 

§ 25.341(a) defines the discrete gust 

velocities up to 50,000 feet. Therefore, 

as a conforming change, we propose to 

amend § 25.341(a)(5)(i) to define 

discrete gust velocities up to 60,000 feet 

for consistency between discrete gust 

and continuous turbulence criteria. 

■ 4. Add a new paragraph § 25.341(c) 

that specifies a ‘‘round-the-clock’’ 

discrete gust criterion and a multi-axis 

discrete gust criterion for airplanes 

equipped with wing-mounted engines. 

Following an accident in which an 

airplane shed a large wing-mounted 

nacelle, the National Transportation 

Safety Board (NTSB) recommended that 

the FAA amend the design load 

requirements to consider multiple axis 

loads encountered during severe 

turbulence (NTSB Safety 

Recommendation A–93–137, November 

15, 1993). This recommendation was 

specifically aimed at gust loads on 

wing-mounted engines. To address the 

NTSB’s concern, the FAA contracted an 

independent organization to develop a 

method of performing multi-axis 

discrete gust analysis for wing-mounted 

nacelles. The results of that study were 

reported to FAA in Stirling Dynamics 

Limited Report No. SDL–571–TR–2 

dated May 1999 (http://www.tc.faa.gov/ 

its/worldpac/techrpt/ar99-62.pdf). The 

recommendations of that report were 

accepted by ARAC and the FAA and are 

set forth in this proposal. This proposal 

would address the NTSB 

recommendation by prescribing two 

dynamic gust criteria for airplanes with 

wing-mounted engines. These are 

known as a ‘‘round-the-clock’’ discrete 

gust criterion, which is a discrete gust 

assumed to occur at any angle normal to 

the flight path, and a multi-axis dual 

discrete gust criterion, which is a pair 

of discrete gusts—one vertical and one 

lateral. These criteria would be set forth 

in a new paragraph § 25.341(c). 

These actions would harmonize 

§ 25.341 with the corresponding EASA 

standards. 

C. Revise ‘‘Design Fuel and Oil Loads’’ 

(§ 25.343), ‘‘High Lift Devices’’ 

(§ 25.345), ‘‘Gyroscopic Loads’’ 

(§ 25.371), ‘‘Speed Control Devices’’ 

(§ 25.373), and ‘‘Control Surface Loads: 

General’’ (§ 25.391) 

Sections 25.343, 25.345, 25.371, 

25.373, and 25.391 specify various 

design load criteria and currently 

require consideration of only the 

discrete load criteria specified in 

§ 25.341(a). However, the FAA believes 

that both the continuous turbulence 

criteria and the discrete gust criteria 

should be included when evaluating 

these other discrete load conditions 

since they account for the response to 

different, but still realistic, atmospheric 

characteristics. Therefore, the FAA 

proposes to add to each of these 

regulations a requirement to evaluate 

the continuous turbulence loads criteria 

in § 25.341(b). These actions would 

harmonize each of these requirements 

with the corresponding EASA 

standards. 

D. Revise ‘‘Engine Torque’’ (§ 25.361) 

and Add a New Section: ‘‘Engine 

Failure Loads’’ (§ 25.362) 

We propose to revise the engine loads 

design requirements for engine mounts, 

auxiliary power unit mounts, engine 

pylons, and adjacent supporting 

airframe structures. The proposed 

amendment would differentiate between 

various engine failure conditions and 

specify design loads criteria that depend 

on the failure condition being 

considered. This proposal is intended to 

ensure that engine mounts and adjacent 

supporting structures are able to 

withstand the most severe loads 

expected in service, which the current 

regulations do not fully address. In 

numerous recent certification programs, 

the FAA has applied special conditions 

(under the provisions of § 21.16) that 

include the engine load design 

requirements proposed here. 

Section 25.361 currently requires that 

the engine mounts and their supporting 

structure be designed for engine torque 

loads combined with flight loads, 

engine torque loads due to maximum 

acceleration, and engine torque loads 

due to malfunction or structural failure. 

Section 25.361 currently specifies 

requirements for turbopropeller engines, 

turbine engines, and reciprocating 

engines, and does not explicitly refer to 

auxiliary power unit (APU) 

installations. 

We propose to revise § 25.361 to (1) 

remove the requirement to assess engine 

torque loads due to engine structural 

failures (this requirement is reestablished in the new § 25.362, 

outlined below); (2) provide specific 

engine torque load criteria for auxiliary 

power unit installations; and (3) remove 

the requirements that apply to 

reciprocating engines. The title of 

§ 25.361 would also be changed from 

‘‘Engine torque’’ to ‘‘Engine and 

auxiliary power unit torque.’’ The 

proposed § 25.361(a) would apply to the 

main engines, while § 25.361(b) would 

apply to APUs. The proposed § 25.362, 

discussed below, would not apply to 

APUs. 

We propose to establish a new 

§ 25.362 that would require engine 

mounts and supporting airframe 

structure be designed for 1g flight loads 

combined with the most critical 

transient dynamic loads and vibrations 

resulting from failure of a blade, shaft, 

bearing or bearing support, or bird strike 

event. 

Studies made by the engine and the 

airframe manufacturers have shown that 

large turbofan engines exhibit two 

distinct classes of sudden deceleration 

events. The first type of event involves 

transient deceleration conditions and 

rapid slowing of the rotating system. 

These events are usually associated with 

temporary loss of power or thrust 

capability, and often result in some 

engine distress, such as blade and/or 

wear strip damage. Examples are high 

power compressor surges and blade tip 

rub during maneuvers, or combinations 

of these events. These events are 

covered by the proposed § 25.361. Based 


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on the frequency of occurrence, the FAA 

considers these events to be limit load 

conditions that require the 1.5 factor of 

safety prescribed in § 25.303 to obtain 

ultimate loads. (The terms ‘‘limit,’’ 

‘‘ultimate,’’ and ‘‘factor of safety’’ are 

discussed in § 25.301, ‘‘Loads,’’ 

§ 25.303, ‘‘Factor of safety,’’ and 

§ 25.305, ‘‘Strength and deformation.’’) 

The second type of event, which 

would be covered by the proposed 

§ 25.362, involves structural failures 

that result in extensive engine damage 

and permanent loss of thrust-producing 

capability. Examples of these types of 

events are fan blade failures, bearing 

failures, and shaft failures. It is evident 

from service history that these more 

severe sudden engine failure events are 

sufficiently infrequent to be considered 

ultimate load conditions. Because of the 

rare occurrence of these events and the 

conservative method in which the loads 

are to be obtained, the FAA proposes 

that these ultimate load conditions be 

applied to engine mounts and pylon 

structure without an additional factor of 

safety. At the same time, to provide 

additional protection for the more 

critical airframe structure, the FAA 

proposes that these ultimate loads be 

multiplied by an additional factor of 

1.25 when applied to the adjacent 

supporting airframe structure. 

For these ultimate load conditions, 

deformation in the engine supporting 

structure would be allowed. However, 

any deformation resulting from these 

conditions must not prevent continued 

safe flight and landing. Lastly, the 

proposed new conditions in § 25.362 

would be required to be treated as 

dynamic conditions, including all 

significant input and response loads. 

These actions would harmonize 

§§ 25.361 and 25.362 with the 

corresponding EASA standards. 

E. Revise ‘‘Control Surface Loads: 

General’’ (§ 25.391), ‘‘Control System’’ 

(§ 25.395), and ‘‘Ground Gust 

Conditions’’ (§ 25.415) 

Section 25.415 currently requires that 

the flight control system be designed for 

loads due to ground gusts when parked 

or while taxiing. Section 25.415 is 

intended to protect the airplane flight 

control system and control surfaces 

from damage in these conditions. 

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. 

Several incidents have occurred in 

which airplanes sustained such 

undetected but severe damage to the 

flight control system due to the dynamic 

effects of ground gust conditions. The 

incidents occurred on airplanes with 

unpowered mechanical controls with 

significant flexibility between the 

control surface and the gust locking 

devices. This flexibility allows dynamic 

loads, greater than the static design gust 

loads, to occur. 

This proposal would revise § 25.415 

to stand alone in regard to the required 

multiplying factors and provide an 

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 

controls restrained by the pilot and/or 

powered system. A 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 of 2.0) would be 

applied for those parts of the control 

system where dynamic effects could be 

significant. A factor lower than 1.6, but 

not less than 1.2, could be used if 

substantiated by a rational analysis. If a 

dynamic factor of 1.2 is accepted, the 

total multiplying factor would then be 

1.2 × 1.25 = 1.5. 

These changes would provide the 

greatest effect on mechanical, 

unpowered control systems which have 

shown the greatest susceptibility to 

damage. Powered control systems have 

hydraulic actuators that naturally 

protect them against dynamic loads due 

to ground gusts. 

We also propose to revise § 25.415 to 

reorganize and clarify the design 

conditions to be considered, and to 

identify the components and parts of the 

control system to which each of the 

conditions apply. 

As a result of the changes to § 25.415, 

we propose removing the references to 

ground gusts in §§ 25.391 and 25.395(b). 

These actions would harmonize 

§§ 25.391, 25.395, and 25.415 with the 

corresponding EASA standards. 

F. Revise ‘‘Rough Air Speed, VRA’’ 

(§ 25.1517) 

Section 25.1517 currently provides 

criteria for establishing the rough air 

speed, VRA, for use as the recommended 

turbulence penetration airspeed to be 

included in the airplane flight manual. 

The rough air speed definition is 

currently based on several 

considerations, including VB. 

We would revise § 25.1517 to remove 

the reference to VB in the definition of 

rough air speed and require that a rough 

air Mach number, MRA, be established 

in addition to rough air speed. Also, the 

reference to § 25.1585, ‘‘Operating 

procedures,’’ is no longer applicable 

since that regulation was modified. The 

reference would therefore be removed. 

VB is the ‘‘design speed for maximum 

gust intensity.’’ This is a design speed 

and is specified in § 25.335(d). VRA is 

the ‘‘rough air speed.’’ This is an 

operational speed to be included in the 

airplane flight manual (AFM) and is 

defined in § 25.1517. In the presence of 

turbulence, the AFM directs the pilot to 

slow to the rough air speed, VRA. 

In general, for a given gust intensity 

(gust speed), the gust loads on an 

airplane increase with increasing 

airplane speed. In the past, the discrete 

gust and continuous turbulence 

requirements of § 25.341 specified the 

highest gust speeds at VB. (Lower gust 

speeds were specified at the higher 

airplane speeds, VC and design diving 

speed, VD.) The operational speed, VRA, 

was established at a value less than or 

equal to VB to ensure the airplane would 

be travelling at a sufficiently low 

airspeed to be able to withstand the 

highest expected gust speed. In this 

way, the airplane would not operate 

beyond its design capability. 

Section 25.341 would be revised as 

described previously, and would no 

longer specify a unique gust speed at 

VB. Rather, the gust speed would be 

assumed constant between VB and VC. 

Therefore, there would be no particular 

reason to link the rough air speed and 

VB. The reference to VB would therefore 

be removed, while the other criteria 

used to define rough air speed are 

maintained. 

Above a certain altitude, the 

maximum operating limit speed, VMO, is 

typically limited by Mach number on 

transport category airplanes. Therefore, 

we propose to revise § 25.1517 to 

require that a rough air Mach number, 

MRA, also be established, in addition to 

rough air speed, VRA. 

These actions would harmonize 

§ 25.1517 with the corresponding EASA 

standards. We would include a minor 

clarifying addition to the rule language 

that would not change the intent of the 

rule. We have notified EASA of this 

addition. 

G. Advisory Material 

The FAA is developing three new 

proposed advisory circulars (ACs) to be 

published concurrently with the 

proposed regulations contained in this 

NPRM. The proposed ACs would 

provide guidance material for 

acceptable means, but not the only 

means, of demonstrating compliance 

with proposed §§ 25.341, 25.362, and 

25.415, respectively. We will accept 

public comments to the following 

proposed ACs on the ‘‘Aviation Safety 

Draft Documents Open for Comment’’ 


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Internet Web site at http://www.faa.gov/ 

aircraft/draft_docs/: 

• AC 25.341–X, ‘‘Dynamic Gust 

Loads.’’ 

• AC 25.362–X, ‘‘Engine Failure 

Loads.’’ 

• AC 25.415–X, ‘‘Ground Gust 

Conditions.’’ 

IV. Regulatory Notices and Analyses 

A. Regulatory Evaluation 

Proposed changes to Federal 

regulations must undergo several 

economic analyses. First, Executive 

Order 12866 and Executive Order 13563 

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 (Pub. L. 96–354) 

requires agencies to analyze the 

economic impact of regulatory changes 

on small entities. Third, the Trade 

Agreements Act (Pub. L. 96–39) 

prohibits agencies from setting 

standards that create unnecessary 

obstacles to the foreign commerce of the 

United States. In developing U.S. 

standards, the Trade Act requires 

agencies to consider international 

standards and, where appropriate, that 

they be the basis of U.S. standards. 

Fourth, the Unfunded Mandates Reform 

Act of 1995 (Pub. L. 104–4) requires 

agencies to prepare a written assessment 

of the costs, benefits, and other effects 

of proposed or final rules that include 

a Federal mandate likely to result in the 

expenditure by State, local, or tribal 

governments, in the aggregate, or by the 

private sector, of $100 million or more 

annually (adjusted for inflation with 

base year of 1995). This portion of the 

preamble summarizes the FAA’s 

analysis of the economic impacts of this 

proposed rule. 

Department of Transportation Order 

DOT 2100.5 prescribes policies and 

procedures for simplification, analysis, 

and review of regulations. If the 

expected cost impact is so minimal that 

a proposed or final rule does not 

warrant a full evaluation, this order 

permits that a statement to that effect 

and the basis for it be included in the 

preamble if a full regulatory evaluation 

of the cost and benefits is not prepared. 

Such a determination has been made for 

this proposed rule. The reasoning for 

this determination follows: 

The FAA proposes to amend the 

airworthiness regulations that would 

harmonize 14 CFR part 25 requirements 

with the corresponding requirements in 

Book 1 of EASA CS–25. Meeting two 

sets of certification requirements raises 

the cost of developing a new transport 

category airplane often with no increase 

in safety. In the interest of fostering 

international trade, lowering the cost of 

aircraft development, making the 

certification process more efficient, and 

improving certification efficiency, the 

FAA tasked ARAC through the LDHWG 

to review existing structures regulations 

and recommend changes that would 

eliminate differences between the U.S. 

and European airworthiness standards, 

while maintaining or improving the 

level of safety in the current regulations. 

All of the proposals below are based 

on LDHWG recommendations, which 

EASA has incorporated into CS–25. The 

FAA agrees with the ARAC 

recommendations as adopted by EASA, 

and we propose to amend part 25 

accordingly, with minor variations in 

wording that do not change the intent. 

The proposed changes would eliminate 

differences between the U.S. and 

European airworthiness standards. 

These efforts are referred to as 

harmonization. 

This proposed rule would revise 

§§ 25.331, ‘‘Symmetric maneuvering 

conditions,’’ 25.341, ‘‘Gust and 

turbulence loads,’’ 25.343, ‘‘Design fuel 

and oil loads,’’ 25.345, ‘‘High lift 

devices,’’ 25.361, ‘‘Engine torque,’’ 

25.371, ‘‘Gyroscopic loads,’’ 25.373, 

‘‘Speed control devices,’’ 25.391, 

‘‘Control surface loads: General,’’ 

25.395, ‘‘Control system,’’ 25.415, 

‘‘Ground gust conditions,’’ and 25.1517, 

‘‘Rough air speed;’’ add a new § 25.362, 

‘‘Engine failure loads’’; and remove 

appendix G to part 25 to remove 

differences with EASA CS–25. The FAA 

has concluded for the reasons 

previously discussed in the preamble 

that the adoption of these EASA 

requirements into the FAA certification 

standards is the most efficient way to 

harmonize these sections and, in so 

doing, the existing level of safety will be 

preserved. 

The FAA estimates that there are no 

costs associated with this proposal. A 

review of current manufacturers of 

transport category aircraft certificated 

under part 25 has revealed that all such 

future aircraft are expected to be 

certificated under both U.S. (part 25) 

and EASA (CS–25). Since future 

certificated transport category aircraft 

are expected to meet the existing EASA 

CS–25 Book 1 requirements, and this 

proposed rule would adopt the same 

EASA requirements, manufacturers 

would incur no additional cost resulting 

from this proposal. The FAA expects the 

costs to be minimal and the benefits to 

be positive but difficult to estimate as 

this proposed rule is one part of a larger 

effort to minimize differences between 

U.S. and EASA certification standards. 

The FAA, however, has not attempted to 

quantify the cost savings that may 

accrue due to these specific proposals, 

beyond noting that while they may be 

minimal, they contribute to a large 

potential harmonization savings. The 

agency concludes that these proposed 

changes would eliminate regulatory 

differences between the airworthiness 

standards of the FAA and EASA 

without affecting current industry 

practices and that savings will result. 

Further analysis is not required. 

The FAA requests comments with 

supporting documentation in regard to 

the conclusions contained in this 

section. 

FAA has, therefore, determined that 

this proposed rule is not a ‘‘significant 

regulatory action’’ as defined in section 

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

‘‘significant’’ as defined in DOT’s 

Regulatory Policies and Procedures. 

B. Regulatory Flexibility Determination 

The Regulatory Flexibility Act of 1980 

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

principle of regulatory issuance that 

agencies shall endeavor, consistent with 

the objectives of the rule and of 

applicable statutes, to fit regulatory and 

informational requirements to the scale 

of the businesses, organizations, and 

governmental jurisdictions subject to 

regulation. To achieve this principle, 

agencies are required to solicit and 

consider flexible regulatory proposals 

and to explain the rationale for their 

actions to assure that such proposals are 

given serious consideration.’’ The RFA 

covers a wide range of small entities, 

including small businesses, not-forprofit organizations, and small 

governmental jurisdictions. 

Agencies must perform a review to 

determine whether a rule will have a 

significant economic impact on a 

substantial number of small entities. If 

the agency determines that it will, the 

agency must prepare a regulatory 

flexibility analysis as described in the 

RFA. 

However, if an agency determines that 

a rule is not expected to have a 

significant economic impact on a 

substantial number of small entities, 

section 605(b) of the RFA provides that 

the head of the agency may so certify, 

and a regulatory flexibility analysis is 

not required. The certification must 

include a statement providing the 

factual basis for this determination, and 

the reasoning should be clear. 

As noted above, the proposed changes 

to part 25 are cost relieving because this 

proposed rule creates a single 

certification standard and removes the 

burden of having to meet two sets of 

certification requirements. The FAA 


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believes that this proposed rule would 

not have a significant economic impact 

on a substantial number of small 

entities. 

The net effect of the proposed rule is 

minimum regulatory cost relief. 

Airplane manufacturers already meet or 

expect to meet this standard. The FAA 

uses the size standards from the Small 

Business Administration for Aircraft 

Manufacturing specifying companies 

having less than 1,500 employees are 

small entities. Given that this proposed 

rule is cost-relieving, and there are no 

small entity manufacturers of part 25 

airplanes with less than 1,500 

employees, the FAA certifies that this 

proposed rule will not have a significant 

economic impact on a substantial 

number of small entities. The FAA 

requests comments regarding this 

determination. Specifically, the FAA 

requests comments on whether the 

proposed rule creates any specific 

compliance costs unique to small 

entities. Please provide detailed 

economic analysis to support any cost 

claims. 

C. International Trade Impact 

Assessment 

The Trade Agreements Act of 1979 

(Pub. L. 96–39) prohibits Federal 

agencies from establishing any 

standards or engaging in related 

activities that create unnecessary 

obstacles to the foreign commerce of the 

United States. Legitimate domestic 

objectives, such as safety, are not 

considered unnecessary obstacles. The 

statute also requires consideration of 

international standards and, where 

appropriate, that they be the basis for 

U.S. standards. The FAA has assessed 

the potential effect of this proposed rule 

and has determined that the proposed 

rule is in accord with the Trade 

Agreements Act as it uses European 

standards as the basis for United States 

regulation. 

D. Unfunded Mandates Assessment 

Title II of the Unfunded Mandates 

Reform Act of 1995 (Pub. L. 104–4) 

requires each Federal agency to prepare 

a written statement assessing the effects 

of any Federal mandate in a proposed or 

final agency rule that may result in an 

expenditure of $100 million or more (in 

1995 dollars) in any one year by State, 

local, and tribal governments, in the 

aggregate, or by the private sector; such 

a mandate is deemed to be a ‘‘significant 

regulatory action.’’ The FAA currently 

uses an inflation-adjusted value of 

$143.1 million in lieu of $100 million. 

This proposed rule does not contain 

such a mandate; therefore, the 

requirements of Title II of the Act do not 

apply. 

E. Paperwork Reduction Act 

The Paperwork Reduction Act of 1995 

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

FAA consider the impact of paperwork 

and other information collection 

burdens imposed on the public. The 

FAA has determined that there is no 

new requirement for information 

collection associated with this proposed 

rule. To the extent you may have 

comments on the information collection 

burdens associated with the aircraft 

certification application process, please 

direct those comments to the 

information collection associated with 

OMB Control Number 2120–0018. 

F. International Compatibility and 

Cooperation 

In keeping with U.S. obligations 

under the Convention on International 

Civil Aviation, it is FAA policy to 

conform to International Civil Aviation 

Organization (ICAO) Standards and 

Recommended Practices to the 

maximum extent practicable. The FAA 

has reviewed the corresponding ICAO 

Standards and Recommended Practices 

and has identified no differences with 

these proposed regulations. 

Executive Order (EO) 13609, 

Promoting International Regulatory 

Cooperation, (77 FR 26413, May 4, 

2012) promotes international regulatory 

cooperation to meet shared challenges 

involving health, safety, labor, security, 

environmental, and other issues and 

reduce, eliminate, or prevent 

unnecessary differences in regulatory 

requirements. The FAA has analyzed 

this action under the policy and agency 

responsibilities of Executive Order 

13609, Promoting International 

Regulatory Cooperation. The agency has 

determined that this action would 

eliminate differences between U.S. 

aviation standards and those of other 

civil aviation authorities by creating a 

single set of certification requirements 

for transport category airplanes that 

would be acceptable in both the United 

States and Europe. 

G. Environmental Analysis 

FAA Order 1050.1E identifies FAA 

actions that are categorically excluded 

from preparation of an environmental 

assessment or environmental impact 

statement under the National 

Environmental Policy Act in the 

absence of extraordinary circumstances. 

The FAA has determined this 

rulemaking action qualifies for the 

categorical exclusion identified in 

paragraph 312f of Order 1050.1E and 

involves no extraordinary 

circumstances. 

V. Executive Order Determinations 

A. Executive Order 13132, Federalism 

The FAA has analyzed this proposed 

rule under the principles and criteria of 

Executive Order 13132, Federalism. The 

agency determined that this action will 

not have a substantial direct effect on 

the States, or the relationship between 

the Federal Government and the States, 

or on the distribution of power and 

responsibilities among the various 

levels of government, and, therefore, 

will not have Federalism implications. 

B. Executive Order 13211, Regulations 

That Significantly Affect Energy Supply, 

Distribution, or Use 

The FAA has analyzed this proposed 

rule under Executive Order 13211, 

Actions Concerning Regulations that 

Significantly Affect Energy Supply, 

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

agency has determined that it is not a 

‘‘significant energy action’’ under the 

executive order and would not be likely 

to have a significant adverse effect on 

the supply, distribution, or use of 

energy. 

VI. Additional Information 

A. Comments Invited 

The FAA invites interested persons to 

participate in this rulemaking by 

submitting written comments, data, or 

views. The agency also invites 

comments relating to the economic, 

environmental, energy, or federalism 

impacts that might result from adopting 

the proposals in this document. The 

most helpful comments reference a 

specific portion of the proposal, explain 

the reason for any recommended 

change, and include supporting data. To 

ensure the docket does not contain 

duplicate comments, commenters 

should send only one copy of written 

comments, or if comments are filed 

electronically, commenters should 

submit only one time. 

The FAA will file in the docket all 

comments it receives, as well as a report 

summarizing each substantive public 

contact with FAA personnel concerning 

this proposed rulemaking. Before acting 

on this proposal, the FAA will consider 

all comments it receives on or before the 

closing date for comments. The FAA 

will consider comments filed after the 

comment period has closed if it is 

possible to do so without incurring 

expense or delay. The agency may 

change this proposal in light of the 

comments it receives. 

Proprietary or Confidential Business 

Information: Commenters should not 


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file proprietary or confidential business 

information in the docket. Such 

information must be sent or delivered 

directly to the person identified in the 

FOR FURTHER INFORMATION CONTACT

section of this document, and marked as 

proprietary or confidential. If submitting 

information on a disk or CD ROM, mark 

the outside of the disk or CD ROM, and 

identify electronically within the disk or 

CD ROM the specific information that is 

proprietary or confidential. 

Under 14 CFR 11.35(b), if the FAA is 

aware of proprietary information filed 

with a comment, the agency does not 

place it in the docket. It is held in a 

separate file to which the public does 

not have access, and the FAA places a 

note in the docket that it has received 

it. If the FAA receives a request to 

examine or copy this information, it 

treats it as any other request under the 

Freedom of Information Act (5 U.S.C. 

552). The FAA processes such a request 

under Department of Transportation 

procedures found in 49 CFR part 7. 

B. Availability of Rulemaking 

Documents 

An electronic copy of rulemaking 

documents may be obtained from the 

Internet by— 

1. Searching the Federal eRulemaking 

Portal at http://www.regulations.gov, 

2. Visiting the FAA’s Regulations and 

Policies Web page at http:// 

www.faa.gov/regulations_policies, or 

3. Accessing the Government Printing 

Office’s Web page at http:// 

www.gpo.gov/fdsys/. 

Copies may also be obtained by 

sending a request to the Federal 

Aviation Administration, Office of 

Rulemaking, ARM–1, 800 Independence 

Avenue SW., Washington, DC 20591, or 

by calling (202) 267–9680. Commenters 

must identify the docket or notice 

number of this rulemaking. 

All documents the FAA considered in 

developing this proposed rule, 

including economic analyses and 

technical reports, may be accessed from 

the Internet through the Federal 

eRulemaking Portal referenced in item 

(1) above. 

List of Subjects in 14 CFR Part 25 

Aircraft, Aviation safety, Reporting 

and recordkeeping requirements. 

The Proposed Amendment 

In consideration of the foregoing, the 

Federal Aviation Administration 

proposes to amend chapter I of title 14, 

Code of Federal Regulations as follows: 

PART 25—AIRWORTHINESS 

STANDARDS: TRANSPORT 

CATEGORY AIRPLANES 

■ 1. The authority citation for part 25 

continues to read as follows: 

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

44702, and 44704. 

■ 2. Amend § 25.331 by revising 

paragraph (c) introductory text and 

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

§ 25.331 Symmetric maneuvering 

conditions. 

* * * * * 

(c) Maneuvering pitching conditions. 

The following conditions must be 

investigated: 

(1) * * * 

(2) Checked maneuver between VA

and VD. Nose-up checked pitching 

maneuvers must be analyzed in which 

the positive limit load factor prescribed 

in § 25.337 is achieved. As a separate 

condition, nose-down checked pitching 

maneuvers must be analyzed in which 

a limit load factor of 0g is achieved. In 

defining the airplane loads, the flight 

deck pitch control motions described in 

paragraphs (c)(2)(i) through (c)(2)(iv) of 

this section must be used: 

(i) The airplane is assumed to be 

flying in steady level flight at any speed 

between VA and VD and the flight deck 

pitch control is moved in accordance 

with the following formula: 

d(t) = d1 sin(wt) for 0 ≤ t ≤ tmax

Where— 

d1 = the maximum available displacement of 

the flight deck pitch control in the initial 

direction, as limited by the control 

system stops, control surface stops, or by 

pilot effort in accordance with 

§ 25.397(b); 

d(t) = the displacement of the flight deck 

pitch control as a function of time. In the 

initial direction, d(t) is limited to d1. In 

the reverse direction, d(t) may be 

truncated at the maximum available 

displacement of the flight deck pitch 

control as limited by the control system 

stops, control surface stops, or by pilot 

effort in accordance with § 25.397(b); 

tmax = 3p/2w; 

w = the circular frequency (radians/second) 

of the control deflection taken equal to the 

undamped natural frequency of the short 

period rigid mode of the airplane, with active 

control system effects included where 

appropriate; but not less than: 

Where— 

V = the speed of the airplane at entry to the 

maneuver. 

VA = the design maneuvering speed 

prescribed in § 25.335(c). 

(ii) For nose-up pitching maneuvers, 

the complete flight deck pitch control 

displacement history may be scaled 

down in amplitude to the extent just 

necessary to ensure that the positive 

limit load factor prescribed in § 25.337 

is not exceeded. For nose-down pitching 

maneuvers, the complete flight deck 

control displacement history may be 

scaled down in amplitude to the extent 

just necessary to ensure that the normal 

acceleration at the center of gravity does 

not go below 0 g. 

(iii) In addition, for cases where the 

airplane response to the specified flight 

deck pitch control motion does not 

achieve the prescribed limit load 

factors, then the following flight deck 

pitch control motion must be used: 

d(t) = d1 sin(wt) for 0 ≤ t ≤ t1

d(t) = d1 for t1 ≤ t ≤ t2

d(t) = d1 sin(w[t + t1 ¥ t2]) for t2 ≤ t ≤ 

tmax

Where— 

t1 = p/2w 

t2 = t1 + Dt 

tmax = t2 + p/w; 

Dt = the minimum period of time necessary 

to allow the prescribed limit load factor 

to be achieved in the initial direction, 

but it need not exceed five seconds (see 

figure below). 


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(iv) In cases where the flight deck 

pitch control motion may be affected by 

inputs from systems (for example, by a 

stick pusher that can operate at high 

load factor as well as at 1 g), then the 

effects of those systems shall be taken 

into account. 

(v) Airplane loads that occur beyond 

the following times need not be 

considered: 

(A) For the nose-up pitching 

maneuver, the time at which the normal 

acceleration at the center of gravity goes 

below 0 g; 

(B) For the nose-down pitching 

maneuver, the time at which the normal 

acceleration at the center of gravity goes 

above the positive limit load factor 

prescribed in § 25.337; 

(C) tmax.. 

■ 3. Amend § 25.341 by revising 

paragraph (a)(5)(i) and paragraph (b), 

and by adding a new paragraph (c) to 

read as follows: 

§ 25.341 Gust and turbulence loads. 

(a) * * * 

(5) * * * 

(i) At airplane speeds between VB and 

VC: Positive and negative gusts with 

reference gust velocities of 56.0 ft/sec 

EAS must be considered at sea level. 

The reference gust velocity may be 

reduced linearly from 56.0 ft/sec EAS at 

sea level to 44.0 ft/sec EAS at 15,000 

feet. The reference gust velocity may be 

further reduced linearly from 44.0 ft/sec 

EAS at 15,000 feet to 20.86 ft/sec EAS 

at 60,000 feet. 

* * * * * 

(b) Continuous turbulence design 

criteria. The dynamic response of the 

airplane to vertical and lateral 

continuous turbulence must be taken 

into account. The dynamic analysis 

must take into account unsteady 

aerodynamic characteristics and all 

significant structural degrees of freedom 

including rigid body motions. The limit 

loads must be determined for all critical 

altitudes, weights, and weight 

distributions as specified in § 25.321(b), 

and all critical speeds within the ranges 

indicated in § 25.341(b)(3). 

(1) Except as provided in paragraphs 

(b)(4) and (b)(5) of this section, the 

following equation must be used: 

PL = PL¥1g ± UσA 

Where— 

PL = limit load; 

PL–1g = steady 1 g load for the condition; 

A = ratio of root-mean-square incremental 

load for the condition to root-meansquare turbulence velocity; and 

Uσ = limit turbulence intensity in true 

airspeed, specified in paragraph (b)(3) of 

this section. 

(2) Values of A must be determined 

according to the following formula: 

Where— 

H(W) = the frequency response function, 

determined by dynamic analysis, that 

relates the loads in the aircraft structure 

to the atmospheric turbulence; and 

F(W) = normalized power spectral density of 

atmospheric turbulence given by— 

Where— 

W = reduced frequency, radians per foot; and 

L = scale of turbulence = 2,500 ft. 

(3) The limit turbulence intensities, Uσ, in 

feet per second true airspeed required for 

compliance with this paragraph are— 

(i) At airplane speeds between VB and VC: 

Us = Uσρεφ Fg

Where— 

Usref is the reference turbulence intensity 

that varies linearly with altitude from 90 fps 

(TAS) at sea level to 79 fps (TAS) at 24,000 

feet and is then constant at 79 fps (TAS) up 

to the altitude of 60,000 feet. 

Fg is the flight profile alleviation factor 

defined in paragraph (a)(6) of this section; 

(ii) At speed VD: Us is equal to 1⁄2 the 

values obtained under paragraph 

(b)(3)(i) of this section. 

(iii) At speeds between VC and VD: Uσ

is equal to a value obtained by linear 

interpolation. 

(iv) At all speeds, both positive and 

negative incremental loads due to 

continuous turbulence must be 

considered. 

(4) When an automatic system 

affecting the dynamic response of the 

airplane is included in the analysis, the 

effects of system non-linearities on 

loads at the limit load level must be 

taken into account in a realistic or 

conservative manner. 

(5) If necessary for the assessment of 

loads on airplanes with significant nonlinearities, it must be assumed that the 

turbulence field has a root-mean-square 

velocity equal to 40 percent of the Uσ

values specified in paragraph (b)(3) of 

this section. The value of limit load is 

that load with the same probability of 

exceedance in the turbulence field as 

AUσ of the same load quantity in a 

linear approximated model. 

(c) Supplementary gust conditions for 

wing-mounted engines. For airplanes 

equipped with wing-mounted engines, 

the engine mounts, pylons, and wing 

supporting structure must be designed 

for the maximum response at the nacelle 

center of gravity derived from the 

following dynamic gust conditions 

applied to the airplane: 

(1) A discrete gust determined in 

accordance with § 25.341(a) at each 

angle normal to the flight path, and 

separately, 

(2) A pair of discrete gusts, one 

vertical and one lateral. The length of 

each of these gusts must be 

independently tuned to the maximum 

response in accordance with § 25.341(a). 

The penetration of the airplane in the 

combined gust field and the phasing of 

the vertical and lateral component gusts 

must be established to develop the 

maximum response to the gust pair. In 

the absence of a more rational analysis, 

the following formula must be used for 

each of the maximum engine loads in all 

six degrees of freedom: 


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Where— 

PL = limit load; 

PL¥1g = steady 1g load for the condition; 

LV = peak incremental response load due to 

a vertical gust according to § 25.341(a); 

and 

LL = peak incremental response load due to 

a lateral gust according to § 25.341(a). 

■ 4. Amend § 25.343 by revising 

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

§ 25.343 Design fuel and oil loads. 

* * * * * 

(b) * * * 

(1) * * * 

(ii) The gust and turbulence 

conditions of § 25.341, but assuming 

85% of the gust velocities prescribed in 

§ 25.341(a)(4) and 85% of the turbulence 

intensities prescribed in § 25.341(b)(3). 

* * * * * 

■ 5. Amend § 25.345 by revising 

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

§ 25.345 High lift devices. 

* * * * * 

(c) * * * 

(2) The vertical gust and turbulence 

conditions prescribed in § 25.341. 

* * * * * 

■ 6. Revise § 25.361 to read as follows: 

§ 25.361 Engine and auxiliary power unit 

torque. 

(a) For engine installations— 

(1) Each engine mount, pylon, and 

adjacent supporting airframe structures 

must be designed for the effects of— 

(i) A limit engine torque 

corresponding to takeoff power/thrust 

and, if applicable, corresponding 

propeller speed, acting simultaneously 

with 75% of the limit loads from flight 

condition A of § 25.333(b); 

(ii) A limit engine torque 

corresponding to the maximum 

continuous power/thrust and, if 

applicable, corresponding propeller 

speed, acting simultaneously with the 

limit loads from flight condition A of 

§ 25.333(b); and 

(iii) For turbopropeller installations 

only, in addition to the conditions 

specified in paragraphs (a)(1)(i) and (ii) 

of this section, a limit engine torque 

corresponding to takeoff power and 

propeller speed, multiplied by a factor 

accounting for propeller control system 

malfunction, including quick feathering, 

acting simultaneously with 1g level 

flight loads. In the absence of a rational 

analysis, a factor of 1.6 must be used. 

(2) The limit engine torque to be 

considered under paragraph (a)(1) of 

this section must be obtained by— 

(i) For turbopropeller installations, 

multiplying mean engine torque for the 

specified power/thrust and speed by a 

factor of 1.25; 

(ii) For other turbine engines, the 

limit engine torque must be equal to the 

maximum accelerating torque for the 

case considered. 

(3) The engine mounts, pylons, and 

adjacent supporting airframe structure 

must be designed to withstand 1g level 

flight loads acting simultaneously with 

the limit engine torque loads imposed 

by each of the following conditions to 

be considered separately: 

(i) Sudden maximum engine 

deceleration due to malfunction or 

abnormal condition; and 

(ii) The maximum acceleration of 

engine. 

(b) For auxiliary power unit 

installations, the power unit mounts 

and adjacent supporting airframe 

structure must be designed to withstand 

1g level flight loads acting 

simultaneously with the limit torque 

loads imposed by each of the following 

conditions to be considered separately: 

(1) Sudden maximum auxiliary power 

unit deceleration due to malfunction or 

abnormal condition or structural failure; 

and 

(2) The maximum acceleration of the 

auxiliary power unit. 

■ 7. Add a new § 25.362 to read as 

follows: 

§ 25.362 Engine failure loads. 

(a) For engine mounts, pylons, and 

adjacent supporting airframe structure, 

an ultimate loading condition must be 

considered that combines 1g flight loads 

with the most critical transient dynamic 

loads and vibrations, as determined by 

dynamic analysis, resulting from failure 

of a blade, shaft, bearing or bearing 

support, or bird strike event. Any 

permanent deformation from these 

ultimate load conditions must not 

prevent continued safe flight and 

landing. 

(b) The ultimate loads developed from 

the conditions specified in paragraph (a) 

of this section are to be— 

(1) Multiplied by a factor of 1.0 when 

applied to engine mounts and pylons; 

and 

(2) Multiplied by a factor of 1.25 

when applied to adjacent supporting 

airframe structure. 

■ 8. Revise § 25.371 to read as follows: 

§ 25.371 Gyroscopic loads. 

The structure supporting any engine 

or auxiliary power unit must be 

designed for the loads, including 

gyroscopic loads, arising from the 

conditions specified in §§ 25.331, 

25.341, 25.349, 25.351, 25.473, 25.479, 

and 25.481, with the engine or auxiliary 

power unit at the maximum rotating 

speed appropriate to the condition. For 

the purposes of compliance with this 

paragraph, the pitch maneuver in 

§ 25.331(c)(1) must be carried out until 

the positive limit maneuvering load 

factor (point A2 in § 25.333(b)) is 

reached. 

■ 9. Amend § 25.373 by revising 

paragraph (a) to read as follows: 

§ 25.373 Speed control devices. 

* * * * * 

(a) The airplane must be designed for 

the symmetrical maneuvers prescribed 

in §§ 25.333 and 25.337, the yawing 

maneuvers in § 25.351, and the vertical 

and lateral gust and turbulence 

conditions prescribed in § 25.341(a) and 

(b) at each setting and the maximum 

speed associated with that setting; and 

* * * * * 

■ 10. Amend § 25.391 by revising the 

introductory text to read 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— 

* * * * * 

■ 11. Amend § 25.395 by revising 

paragraph (b) to read as follows: 

§ 25.395 Control system. 

* * * * * 

(b) The system limit loads of 

paragraph (a) of this section need not 

exceed the loads that can be produced 

by the pilot (or pilots) and by automatic 

or power devices operating the controls. 

* * * * * 

■ 12. Revise § 25.415 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 

hinge moments H must be computed 

from the formula: 

H = K (1⁄2) ro V2 c S 

Where— 

K = hinge moment factor for ground gusts 

derived in paragraph (c) of this section; 

ro = density of air at sea level; 

V = 65 knots relative to the aircraft; 

S = area of the control surface aft of the hinge 

line; 

c = mean aerodynamic chord of the control 

surface aft of the hinge line. 


wreier-aviles on DSK5TPTVN1PROD with PROPOSALSEP28MY13.020</GPH>
31860 Federal Register / Vol. 78, No. 102 / Tuesday, May 28, 2013 / Proposed Rules 

(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 Elevator full down. 

(d) Elevator .................................................................................................... *±0.75 Elevator full up. 

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

(f) Rudder ....................................................................................................... 0.75 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) of this section 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) of this section to obtain 

limit loads. If a rational analysis is used, 

the additional factor must not be less 

than 1.2. 

(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 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. 

(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 flight deck 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. 

■ 13. Revise § 25.1517 to read as 

follows: 

§ 25.1517 Rough air speed, VRA. 

(a) A rough air speed, VRA, for use as 

the recommended turbulence 

penetration airspeed, and a rough air 

Mach number, MRA, for use as the 

recommended turbulence penetration 

Mach number, must be established. 

VRA/MRA must be sufficiently less than 

VMO/MMO to ensure that likely speed 

variation during rough air encounters 

will not cause the overspeed warning to 

operate too frequently. 

(b) At altitudes where VMO is not 

limited by Mach number, in the absence 

of a rational investigation substantiating 

the use of other values, VRA must be less 

than VMO–35 KTAS. 

(c) At altitudes where VMO is limited 

by Mach number, MRA may be chosen 

to provide an optimum margin between 

low and high speed buffet boundaries. 

■ 14. Remove and reserve appendix G to 

part 25. 

Issued under authority provided by 49 

U.S.C. 106(f), 44701(a), and 44703 in 

Washington, DC, on May 6, 2013. 

Dorenda D. Baker, 

Director, Aircraft Certification Service. 

[FR Doc. 2013–12445 Filed 5–24–13; 8:45 am] 

BILLING CODE 4910–13–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 39 

[Docket No. FAA–2008–0288; Directorate 

Identifier 2006–SW–25–AD] 

RIN 2120–AA64 

Airworthiness Directives; Bell 

Helicopter Textron, Inc., Helicopters 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Supplemental notice of 

proposed rulemaking (SNPRM); 

reopening of comment period. 

SUMMARY: We are revising an earlier 

proposed airworthiness directive (AD) 

for Bell Helicopter Textron, Inc. (Bell), 

Model 214B and B–1 helicopters, which 

proposed to require inspecting certain 

pylon support spindle assemblies 

(spindles) for any corrosion, or a nick, 

scratch, dent, or crack, and repairing or 

replacing any unairworthy spindle 

before further flight. This SNPRM 

proposes to revise those requirements 

by updating the cost of compliance, 

revising the recording requirements, 

adding a requirement to reduce the 

retirement life of an installed spindle, 

and adding Bell Model 214ST to the 

applicability. 

DATES: We must receive comments on 

this proposed AD by July 29, 2013. 

ADDRESSES: You may send comments by 

any of the following methods: 

• Federal eRulemaking Docket: Go to 

http://www.regulations.gov. Follow the 

online instructions for sending your 

comments electronically. 

• Fax: 202–493–2251. 

• Mail: Send comments to the U.S. 

Department of Transportation, Docket 

Operations, M–30, West Building 

Ground Floor, Room W12–140, 1200 

New Jersey Avenue SE., Washington, 

DC 20590–0001. 

• Hand Delivery: Deliver to the 

‘‘Mail’’ address between 9 a.m. and 5 


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