[Federal Register Volume 79, Number 238 (Thursday, December 11, 2014)]
[Rules and Regulations]
[Pages 73462-73469]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2014-28938]
=======================================================================
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No.: FAA-2013-0142; Amdt. No. 25-141]
RIN 2120-AK12
Harmonization of Airworthiness Standards--Gust and Maneuver Load
Requirements
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final rule.
-----------------------------------------------------------------------
SUMMARY: This final rule amends certain airworthiness regulations for
transport category airplanes, based on recommendations from the FAA-
sponsored Aviation Rulemaking Advisory Committee (ARAC). This amendment
eliminates regulatory differences between the airworthiness standards
of the FAA and European Aviation Safety Agency (EASA). It does not add
new requirements beyond what manufacturers currently meet for EASA
certification and does not affect current industry design practices.
This final rule revises the pitch maneuver design loads criteria;
revises the gust and turbulence design loads criteria; revises the
application of gust loads to engine mounts, high lift devices, and
other control surfaces; adds a ``round-the-clock'' discrete gust
criterion and a multi-axis discrete gust criterion for airplanes
equipped with wing-mounted engines; revises the engine torque loads
criteria; adds an engine failure dynamic load condition; revises the
ground gust design loads criteria; revises the criteria used to
establish the rough air design speed; and requires the establishment of
a rough air Mach number.
DATES: Effective February 9, 2015.
ADDRESSES: For information on where to obtain copies of rulemaking
documents and other information related to this final rule, see ``How
To Obtain Additional Information'' in the SUPPLEMENTARY INFORMATION
section of this document.
FOR FURTHER INFORMATION CONTACT: For technical questions concerning
this action, contact Todd Martin, Airframe and Cabin Safety Branch,
ANM-115,
[[Page 73463]]
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
[email protected].
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 [email protected].
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 Final Rule
The FAA is amending Title 14, Code of Federal Regulations (14 CFR)
Part 25 as described below. This action harmonizes part 25 requirements
with the corresponding requirements in Book 1 of the EASA Certification
Specifications and Acceptable Means of Compliance for Large Aeroplanes
(CS-25). As such, this action--
1. Revises Sec. 25.331, ``Symmetric maneuvering conditions,'' to
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. The introductory paragraph, Sec. 25.331(c), is
revised by moving some criteria to Sec. 25.331(c)(2) where those
criteria apply.
2. Removes appendix G to part 25, ``Continuous Gust Design
Criteria,'' and Sec. 25.341(b) now clearly sets forth the continuous
turbulence requirement.
3. Revises Sec. 25.341, ``Gust and turbulence loads,'' to--
Remove the optional mission analysis method currently
specified in appendix G in favor of the design envelope analysis
method.
Update the turbulence intensity criteria in Sec.
25.341(b) to take into account in-service measurements of derived gust
intensities.
Update Sec. 25.341(a) to require evaluation of discrete
gust conditions at airplane speeds from design speed for maximum gust
intensity, VB, to design cruising speed, VC,
(previously required only at VC) and to specify reference
gust velocities up to 60,000 feet, rather than the previously specified
50,000 feet.
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.
4. Revises Sec. 25.343, ``Design fuel and oil loads,'' Sec.
25.345, ``High lift devices,'' Sec. 25.371, ``Gyroscopic loads,''
Sec. 25.373, ``Speed control devices,'' and Sec. 25.391, ``Control
surface loads: General,'' by adding to each of these regulations a
requirement to evaluate the continuous turbulence loads criteria in
Sec. 25.341(b).
5. Revises Sec. 25.361, ``Engine and auxiliary power unit
torque,'' to--
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).
Provide specific engine torque load criteria for auxiliary
power unit installations.
Remove the requirements that apply to reciprocating
engines.
Change the title of Sec. 25.361 from ``Engine torque'' to
``Engine and auxiliary power unit torque.''
6. Adds new Sec. 25.362, ``Engine failure loads,'' to 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.
7. Revises Sec. 25.391, ``Control surface loads: General,'' and
Sec. 25.395, ``Control system,'' to remove references to the ground
gust requirements in Sec. 25.415.
8. Revises Sec. 25.415, ``Ground gust conditions'' to--
Reorganize and clarify the design conditions to be
considered.
Identify the components and parts of the control system to
which each of the conditions apply.
Make it stand alone in regard to the required multiplying
factors and to provide an additional multiplying factor to account for
dynamic amplification.
9. Revises Sec. 25.1517, ``Rough air speed, VRA'' to
remove the reference to VB in the definition of rough air speed and to
require that a rough air Mach number, MRA, be established in addition
to rough air speed. Also, this action removes the reference to Sec.
25.1585, ``Operating procedures,'' because it is no longer applicable
since that regulation was modified.
II. Background
A. Statement of the Problem
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.
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. The LDHWG developed recommendations,
which EASA has incorporated into CS-25 with some changes. The FAA
agrees with the ARAC recommendations as adopted by EASA, and this final
rule amends part 25 accordingly.
B. Summary of the NPRM
On May 6, 2013, the FAA issued a Notice of Proposed Rulemaking
(NPRM), Notice No. 25-139,\1\ Docket No. FAA-2013-0142, to amend
Sec. Sec. 25.331, 25.341, 25.343, 25.345, 25.361, 25.371, 25.373,
25.391, 25.395, 25.415, and 25.1517; to add Sec. 25.362; and to remove
appendix G of 14 CFR part 25. That NPRM was published in the Federal
Register on May 28, 2013 (78 FR 31851). In the NPRM, the FAA proposed
to (1) revise the pitch maneuver design loads criteria; (2) revise the
gust and turbulence design loads criteria; (3) revise the application
of gust loads to engine mounts, high lift devices, and other control
surfaces; (4) add a ``round-the-clock'' discrete gust criterion and a
multi-axis discrete gust criterion for airplanes equipped with wing-
mounted engines; (5) revise the engine torque loads criteria and add an
engine failure dynamic load condition; (6) revise the ground gust
design loads criteria; (7) revise the criteria used to establish the
rough air design speed; and (8) require the establishment of a rough
air Mach number.
---------------------------------------------------------------------------
\1\ On April 16, 2014, the Federal Register published a
correction (79 FR 21413) changing the Notice No. to ``13-04'' for
the NPRM that published May 28, 2013 (78 FR 31851) and for
subsequent NPRM corrections that published June 24, 2013 (78 FR
37722) and July 16, 2013 (78 FR 42480).
---------------------------------------------------------------------------
[[Page 73464]]
The FAA proposed these changes to eliminate regulatory differences
between the airworthiness standards of the FAA and EASA. The NPRM
comment period closed on August 26, 2013.
On June 24, 2013, the Federal Register published a correction to
the NPRM to correct three equations in the proposed amendments to Sec.
25.341 (78 FR 37722). On July 16, 2013, the Federal Register published
a second correction to one equation in the proposed amendments to Sec.
25.341 (78 FR 42480). The equations in this final rule have not changed
from those in the corrected NPRM.
C. General Overview of Comments
The FAA received two comments. One commenter supported the NPRM and
the ongoing international harmonization of certification requirements.
The other comment addressed Sec. 25.341 and is discussed below.
III. Discussion of Public Comments and Final Rule
A. Section 25.341, ``Gust and Turbulence Loads''
Section 25.341(a)(6) uses the term Zmo, which is the
maximum operating altitude, in feet, specifically defined in Sec.
25.1527. A commenter noted that the units for the term Zmo
are not provided in the current rule. While Sec. 25.341(a)(6) was not
being revised as part of this rulemaking, the commenter recommended
that this paragraph be revised to include the appropriate units for
Zmo (feet) for ease of reference. We agree, and revise the
rule as recommended.
B. Section 25.415, ``Ground Gust Conditions''
After further FAA review of what we proposed by NPRM, we now
specify that control system gust locks are to be taken into account
only when the airplane is so equipped. As proposed, Sec. 25.415 would
have required that the airplane be evaluated while taxiing with the
controls locked and unlocked, and while parked with the controls
locked. However, many transport category airplanes with powered flight
controls do not have control system gust locks. As noted in the NPRM,
these airplanes rely on their hydraulic actuators to provide protection
from ground gusts. We, therefore, now revise Sec. 25.415 to clarify
that, for all airplanes, the ground gust conditions apply when the
airplane is taxiing and while parked. For airplanes that include
control system gust locks, the taxiing condition must be evaluated with
the controls locked and unlocked, and the parked condition must be
evaluated with the controls locked. Airplanes not equipped with gust
locks are to be evaluated in their normal configuration while taxiing
and while parked. With these changes to Sec. 25.415, the rule wording
will no longer be exactly the same as CS 25.415; however, the intent of
the two rules is the same in how airplanes with and without gust locks
are evaluated.
C. Advisory Material
On May 31, 2013, the FAA published and solicited public comments on
three proposed ACs that describe acceptable means for showing
compliance with the NPRM's proposed regulations. The comment period for
the proposed ACs closed on September 26, 2013. The FAA did not receive
any comments on the proposed ACs. Concurrently with this final rule,
the FAA is issuing the following final ACs to provide guidance material
for the new regulations adopted by this amendment:
AC 25.341-1, ``Dynamic Gust Loads.''
AC 25.362-1, ``Engine Failure Loads.''
AC 25.415-1, ``Ground Gust Conditions.''
IV. Regulatory Notices and Analyses
A. Regulatory Evaluation
Changes to Federal regulations must undergo several economic
analyses. First, Executive Order 12866 and Executive Order 13563 direct
that each Federal agency shall propose or adopt a regulation only upon
a reasoned determination that the benefits of the intended regulation
justify its costs. Second, the Regulatory Flexibility Act of 1980
(Public Law 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 final 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 final rule. The reasoning
for this determination follows.
The FAA is amending certain airworthiness standards for transport
category airplanes. Adopting this final rule will eliminate regulatory
differences between the airworthiness standards of the FAA and EASA.
This final rule does not add new requirements beyond what manufacturers
currently meet for EASA certification and does not affect current
industry design practices. Meeting two sets of certification
requirements raises the cost of developing new transport category
airplanes with little to no increase in safety. In the interest of
fostering international trade, lowering the cost of manufacturing new
transport category airplanes, and making the certification process more
efficient, the FAA, EASA, and several industry working groups came
together to create, to the maximum extent possible, a single set of
certification requirements that would be accepted in both the United
States and Europe. Therefore, as a result of these harmonization
efforts, the FAA is amending the airworthiness regulations described in
section I of this final rule, ``Overview of Final Rule.'' This action
harmonizes part 25 requirements with the corresponding requirements in
EASA CS-25 Book 1.
Currently, all manufacturers of transport category airplanes,
certificated under part 25 are expected to continue their current
practice of compliance with the EASA certification requirements in CS-
25 Book 1. Since future certificated transport airplanes are expected
to meet CS-25 Book 1, and this rule simply adopts EASA requirements,
manufacturers will incur minimal or no additional cost resulting from
this final rule. The FAA made this same determination in the NPRM and
received no comments.
The FAA has, therefore, determined that this final 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.
[[Page 73465]]
B. Regulatory Flexibility Determination
The Regulatory Flexibility Act of 1980 (Public Law 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.
In the NPRM, the FAA determined that this rule would not impose
more than minimal cost.
The FAA believes that this final rule does not have a significant
economic impact on a substantial number of small entities for the
following reasons. We did not receive any comments from small entities.
All United States transport category airplane manufacturers exceed the
Small Business Administration small-entity criteria of 1,500 employees.
Therefore, as provided in section 605(b), the head of the FAA certifies
that this rulemaking will not result in a significant economic impact
on a substantial number of small entities.
C. International Trade Impact Assessment
The Trade Agreements Act of 1979 (Pub. L. 96-39), as amended by the
Uruguay Round Agreements Act (Pub. L. 103-465), prohibits Federal
agencies from establishing standards or engaging in related activities
that create unnecessary obstacles to the foreign commerce of the United
States. Pursuant to these Acts, the establishment of standards is not
considered an unnecessary obstacle to the foreign commerce of the
United States, so long as the standard has a legitimate domestic
objective, such the protection of safety, and does not operate in a
manner that excludes imports that meet this objective. The statute also
requires consideration of international standards and, where
appropriate, that they be the basis for U.S. standards. The FAA has
assessed the potential effect of this final rule and determined that it
is in accord with the Trade Agreements Act as the rule furthers the
legitimate domestic objectives of safety, creates no unnecessary
obstacles to foreign commerce, does not exclude imports, and uses
European standards as the basis for United States regulation.
D. Unfunded Mandates Assessment
Title II of the Unfunded Mandates Reform Act of 1995 (Public Law
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 $151 million in lieu of $100
million. This final 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 final rule.
F. International Compatibility and Cooperation
(1) In keeping with U.S. obligations under the Convention on
International Civil Aviation, it is FAA policy to conform to
International Civil Aviation Organization (ICAO) Standards and
Recommended Practices to the maximum extent practicable. The FAA has
reviewed the corresponding ICAO Standards and Recommended Practices and
has identified no differences with these regulations.
(2) 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 final rule under the principles and
criteria of Executive Order 13132, Federalism. The agency determined
that this action will not have a substantial direct effect on the
States, or the relationship between the Federal Government and the
States, or on the distribution of power and responsibilities among the
various levels of government, and, therefore, does not have Federalism
implications.
B. Executive Order 13211, Regulations That Significantly Affect Energy
Supply, Distribution, or Use
The FAA analyzed this final rule under Executive Order 13211,
Actions Concerning Regulations that Significantly Affect Energy Supply,
Distribution, or Use (May 18, 2001). The agency has determined that it
is not a ``significant energy action'' under the executive order and it
is not likely to have a significant adverse effect on the supply,
distribution, or use of energy.
[[Page 73466]]
VI. How To Obtain Additional Information
A. Rulemaking Documents
An electronic copy of a rulemaking document may be obtained by
using the Internet--
1. Search the Federal eRulemaking Portal (http://www.regulations.gov),
2. Visit the FAA's Regulations and Policies Web page at http://www.faa.gov/regulations_policies/, or
3. Access the Government Printing Office's Web page at http://www.gpo.gov/fdsys/.
Copies may also be obtained by sending a request (identified by
notice, amendment, or docket number of this rulemaking) to the Federal
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence
Avenue SW., Washington, DC 20591; or by calling (202) 267-9680.
B. Comments Submitted to the Docket
Comments received may be viewed by going to http://www.regulations.gov and following the online instructions to search the
docket number for this action. Anyone is able to search the electronic
form of all comments received into any of the FAA's dockets by the name
of the individual submitting the comment (or signing the comment, if
submitted on behalf of an association, business, labor union, etc.).
C. Small Business Regulatory Enforcement Fairness Act
The Small Business Regulatory Enforcement Fairness Act (SBREFA) of
1996 requires the FAA to comply with small entity requests for
information or advice about compliance with statutes and regulations
within its jurisdiction. A small entity with questions regarding this
document, may contact its local FAA official, or the person listed
under the FOR FURTHER INFORMATION CONTACT heading at the beginning of
the preamble. To find out more about SBREFA on the Internet, visit
http://www.faa.gov/regulations_policies/rulemaking/sbre_act/.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
The Amendment
In consideration of the foregoing, the Federal Aviation
Administration amends part 25 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:
* * * * *
(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
(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 <=t
max
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 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] TR11DE14.023
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 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 necessary to ensure that the
normal acceleration at the center of gravity does not go below 0g.
(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 73467]]
[GRAPHIC] [TIFF OMITTED] TR11DE14.024
(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 1g), 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 0g;
(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 paragraphs (a)(5)(i), (a)(6), and
(b), and by adding 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.
* * * * *
(6) * * *
Zmo = Maximum operating altitude defined in Sec. 25.1527
(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 (5) of this
section, the following equation must be used:
PL = PL-1g U[sigma]A
Where--
PL = limit load;
PL-1g = steady 1g 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] TR11DE14.025
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] TR11DE14.026
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
[[Page 73468]]
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:
[GRAPHIC] [TIFF OMITTED] TR11DE14.027
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(a) and (b),
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(a) and (b).
* * * * *
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, abnormal condition, or structural failure; and
(2) The maximum acceleration of the auxiliary power unit.
0
7. Add 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 airplane is subjected to a
horizontal 65-knot ground gust from any direction while taxiing and
while parked. For airplanes equipped with control system gust locks,
the taxiing condition must be evaluated with the controls locked and
unlocked, and the parked condition must be evaluated with the controls
locked.
(b) The control system and surface loads due to ground gust may be
[[Page 73469]]
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.
(c) The hinge moment factor K for ground gusts must be taken from
the following table:
------------------------------------------------------------------------
Surface K Position of controls
------------------------------------------------------------------------
(1) Aileron......................... 0.75 Control column locked
or lashed in mid-
position.
(2) Aileron......................... * 0.5
0
(3) Elevator........................ * 0.7
5
(4) Elevator........................ * 0.7
5
(5) Rudder.......................... 0.75 Rudder in neutral.
(6) 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 substantiating a different
dynamic factor, 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 any control
systems 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 any control systems 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,
or where control locks are not provided, the following apply:
(1) The control surfaces, the control system stops nearest the
surfaces, and the parts of any control systems 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 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.
Appendix G to Part 25 [Removed and Reserved]
0
14. Remove and reserve appendix G to part 25.
Issued under authority provided by 49 U.S.C. 106(f) and 44701(a)
in Washington, DC, on November 14, 2014.
Michael P. Huerta,
Administrator.
[FR Doc. 2014-28938 Filed 12-10-14; 8:45 am]
BILLING CODE 4910-13-P