Document ID: FAA-2013-0142-0001
Agency: faa
Document Type: Proposed Rule
Title: Harmonization of Airworthiness Standards: Gust and Maneuver Load Requirements
Posted Date: 2013-05-28T04:00Z

[Federal Register Volume 78, Number 102 (Tuesday, May 28, 2013)]
[Proposed Rules]
[Pages 31851-31860]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2013-12445]

=======================================================================
-----------------------------------------------------------------------

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-the-clock'' 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 Sec.  25.331, ``Symmetric maneuvering conditions;''

[[Page 31852]]

    2. Amend Sec.  25.341, ``Gust and turbulence loads;''
    3. Amend Sec.  25.343, ``Design fuel and oil loads;''
    4. Amend Sec.  25.345, ``High lift devices;''
    5. Amend Sec.  25.361, ``Engine torque;''
    6. Add Sec.  25.362, ``Engine failure loads;''
    7. Amend Sec.  25.371, ``Gyroscopic loads;''
    8. Amend Sec.  25.373, ``Speed control devices;''
    9. Amend Sec.  25.391, ``Control surface loads: General;''
    10. Amend Sec.  25.395, ``Control system;''
    11. Amend Sec.  25.415, ``Ground gust conditions;''
    12. Amend Sec.  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'' (Sec.  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 Sec.  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, Sec.  25.331(c), by 
moving some criteria to Sec.  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 Sec.  25.331 with the corresponding 
EASA standards.

B. Revise ``Gust and Turbulence Loads'' (Sec.  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 Sec.  
25.341(a) Discrete Gust Design Criteria (representing a singular gust), 
and Sec.  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 Sec.  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 Sec.  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 Sec.  
25.341(a) (Amendment 25-86, 61 FR 5218, dated February 9, 1996) to 
provide a revised

[[Page 31853]]

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 Sec.  
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 non-
linearity be considered in a realistic or conservative manner.
    3. Revise Sec.  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, Sec.  25.341(a) defines the discrete gust 
velocities up to 50,000 feet. Therefore, as a conforming change, we 
propose to amend Sec.  25.341(a)(5)(i) to define discrete gust 
velocities up to 60,000 feet for consistency between discrete gust and 
continuous turbulence criteria.

0
4. Add a new paragraph Sec.  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 Sec.  
25.341(c).
    These actions would harmonize Sec.  25.341 with the corresponding 
EASA standards.

C. Revise ``Design Fuel and Oil Loads'' (Sec.  25.343), ``High Lift 
Devices'' (Sec.  25.345), ``Gyroscopic Loads'' (Sec.  25.371), ``Speed 
Control Devices'' (Sec.  25.373), and ``Control Surface Loads: 
General'' (Sec.  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 Sec.  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 Sec.  25.341(b). These 
actions would harmonize each of these requirements with the 
corresponding EASA standards.

D. Revise ``Engine Torque'' (Sec.  25.361) and Add a New Section: 
``Engine Failure Loads'' (Sec.  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 Sec.  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 Sec.  25.361 to (1) remove the requirement to 
assess engine torque loads due to engine structural failures (this 
requirement is re-established in the new Sec.  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 Sec.  25.361 would also be changed 
from ``Engine torque'' to ``Engine and auxiliary power unit torque.'' 
The proposed Sec.  25.361(a) would apply to the main engines, while 
Sec.  25.361(b) would apply to APUs. The proposed Sec.  25.362, 
discussed below, would not apply to APUs.
    We propose to establish a new Sec.  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 Sec.  25.361. Based

[[Page 31854]]

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 Sec.  25.303 to obtain ultimate loads. (The terms ``limit,'' 
``ultimate,'' and ``factor of safety'' are discussed in Sec.  25.301, 
``Loads,'' Sec.  25.303, ``Factor of safety,'' and Sec.  25.305, 
``Strength and deformation.'')
    The second type of event, which would be covered by the proposed 
Sec.  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 Sec.  25.362 would 
be required to be treated as dynamic conditions, including all 
significant input and response loads.
    These actions would harmonize Sec. Sec.  25.361 and 25.362 with the 
corresponding EASA standards.

E. Revise ``Control Surface Loads: General'' (Sec.  25.391), ``Control 
System'' (Sec.  25.395), and ``Ground Gust Conditions'' (Sec.  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 Sec.  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 x 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 Sec.  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 Sec.  25.415, we propose removing the 
references to ground gusts in Sec. Sec.  25.391 and 25.395(b).
    These actions would harmonize Sec. Sec.  25.391, 25.395, and 25.415 
with the corresponding EASA standards.

F. Revise ``Rough Air Speed, VRA'' (Sec.  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 Sec.  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 Sec.  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 Sec.  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 
Sec.  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 Sec.  
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 Sec.  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 Sec.  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 Sec. Sec.  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''

[[Page 31855]]

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 Sec. Sec.  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 Sec.  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-for-profit 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

[[Page 31856]]

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

[[Page 31857]]

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

0
1. The authority citation for part 25 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, and 44704.

0
2. Amend Sec.  25.331 by revising paragraph (c) introductory text and 
paragraph (c)(2) to read as follows:

Sec.  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 Sec.  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:

[delta](t) = [delta]1 sin([omega]t) for 0 <= t <= 
tmax

Where--

[delta]1 = 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 Sec.  25.397(b);
[delta](t) = the displacement of the flight deck pitch control as a 
function of time. In the initial direction, [delta](t) is limited to 
[delta]1. In the reverse direction, [delta](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 Sec.  
25.397(b);
tmax = 3[pi]/2[omega];
    [omega] = 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:
[GRAPHIC] [TIFF OMITTED] TP28MY13.016

Where--
V = the speed of the airplane at entry to the maneuver.
VA = the design maneuvering speed prescribed in Sec.  
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 Sec.  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:

[delta](t) = [delta]1 sin([omega]t) for 0 <= t <= 
t1
[delta](t) = [delta]1 for t1 <= t <= 
t2
[delta](t) = [delta]1 sin([omega][t + t1 - 
t2]) for t2 <= t <= tmax

Where--

t1 = [pi]/2[omega]
t2 = t1 + [Delta]t
tmax = t2 + [pi]/[omega];
[Delta]t = 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).

[[Page 31858]]

[GRAPHIC] [TIFF OMITTED] TP28MY13.017

    (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 Sec.  25.337;
    (C) tmax..
0
3. Amend Sec.  25.341 by revising paragraph (a)(5)(i) and paragraph 
(b), and by adding a new paragraph (c) to read as follows:

Sec.  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 Sec.  25.321(b), and all critical speeds 
within the ranges indicated in Sec.  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  U[sigma]A

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-mean-square turbulence velocity; and
U[sigma] = 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:
[GRAPHIC] [TIFF OMITTED] TP28MY13.018

Where--

H([Omega]) = the frequency response function, determined by dynamic 
analysis, that relates the loads in the aircraft structure to the 
atmospheric turbulence; and
[Phi]([Omega]) = normalized power spectral density of atmospheric 
turbulence given by--
[GRAPHIC] [TIFF OMITTED] TP28MY13.019

Where--

[Omega] = reduced frequency, radians per foot; and
L = scale of turbulence = 2,500 ft.

    (3) The limit turbulence intensities, U[sigma], in feet per 
second true airspeed required for compliance with this paragraph 
are--
    (i) At airplane speeds between VB and VC: 
U[sigma] = U[sigma]ref Fg

Where--

    U[sigma]ref 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: U[sigma] is equal to \1/2\ 
the values obtained under paragraph (b)(3)(i) of this section.
    (iii) At speeds between VC and VD: U[sigma] 
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 non-linearities, it must be assumed that the turbulence 
field has a root-mean-square velocity equal to 40 percent of the 
U[sigma] 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 AU[sigma] 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 Sec.  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 Sec.  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:

[[Page 31859]]

[GRAPHIC] [TIFF OMITTED] TP28MY13.020

Where--

PL = limit load;
PL-1g = steady 1g load for the condition;
LV = peak incremental response load due to a vertical 
gust according to Sec.  25.341(a); and
LL = peak incremental response load due to a lateral gust 
according to Sec.  25.341(a).

0
4. Amend Sec.  25.343 by revising paragraph (b)(1)(ii) to read as 
follows:

Sec.  25.343  Design fuel and oil loads.

* * * * *
    (b) * * *
    (1) * * *
    (ii) The gust and turbulence conditions of Sec.  25.341, but 
assuming 85% of the gust velocities prescribed in Sec.  25.341(a)(4) 
and 85% of the turbulence intensities prescribed in Sec.  25.341(b)(3).
* * * * *
0
5. Amend Sec.  25.345 by revising paragraph (c)(2) to read as follows:

Sec.  25.345  High lift devices.

* * * * *
    (c) * * *
    (2) The vertical gust and turbulence conditions prescribed in Sec.  
25.341.
* * * * *
0
6. Revise Sec.  25.361 to read as follows:

Sec.  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 
Sec.  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 Sec.  
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.
0
7. Add a new Sec.  25.362 to read as follows:

Sec.  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.
0
8. Revise Sec.  25.371 to read as follows:

Sec.  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 Sec. Sec.  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 Sec.  
25.331(c)(1) must be carried out until the positive limit maneuvering 
load factor (point A2 in Sec.  25.333(b)) is reached.
0
9. Amend Sec.  25.373 by revising paragraph (a) to read as follows:

Sec.  25.373  Speed control devices.

* * * * *
    (a) The airplane must be designed for the symmetrical maneuvers 
prescribed in Sec. Sec.  25.333 and 25.337, the yawing maneuvers in 
Sec.  25.351, and the vertical and lateral gust and turbulence 
conditions prescribed in Sec.  25.341(a) and (b) at each setting and 
the maximum speed associated with that setting; and
* * * * *
0
10. Amend Sec.  25.391 by revising the introductory text to read as 
follows:

Sec.  25.391  Control surface loads: General.

    The control surfaces must be designed for the limit loads resulting 
from the flight conditions in Sec. Sec.  25.331, 25.341(a) and (b), 
25.349, and 25.351, considering the requirements for--
* * * * *
0
11. Amend Sec.  25.395 by revising paragraph (b) to read as follows:

Sec.  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.
* * * * *
0
12. Revise Sec.  25.415 to read as follows:

Sec.  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\) [rho]o V\2\ c S

Where--

K = hinge moment factor for ground gusts derived in paragraph (c) of 
this section;
[rho]o = 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.

[[Page 31860]]

    (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....................    *0.5
                                         0
(c) Elevator...................    *0.7
                                         5
(d) Elevator...................    *0.7
                                         5
(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 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.
0
13. Revise Sec.  25.1517 to read as follows:

Sec.  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.
0
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