Source: https://www.federalregister.gov/documents/2014/12/11/2014-28938/harmonization-of-airworthiness-standards-gust-and-maneuver-load-requirements
Timestamp: 2018-07-16 19:06:33
Document Index: 449995633

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73462-73469 (8 pages)
A. Section 25.341, “Gust and Turbulence Loads”
B. Section 25.415, “Ground Gust Conditions”
Appendix G to Part 25 [Removed and Reserved]
https://www.federalregister.gov/d/2014-28938 https://www.federalregister.gov/d/2014-28938
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.
For technical questions concerning this action, contact Todd Martin, Airframe and Cabin Safety Branch, ANM-115, Start Printed Page 73463Transport 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.
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 § 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, § 25.331(c), is revised by moving some criteria to § 25.331(c)(2) where those criteria apply.
2. Removes appendix G to part 25, “Continuous Gust Design Criteria,” and § 25.341(b) now clearly sets forth the continuous turbulence requirement.
3. Revises § 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 § 25.341(b) to take into account in-service measurements of derived gust intensities.
Update § 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 § 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 § 25.343, “Design fuel and oil loads,” § 25.345, “High lift devices,” § 25.371, “Gyroscopic loads,” § 25.373, “Speed control devices,” and § 25.391, “Control surface loads: General,” by adding to each of these regulations a requirement to evaluate the continuous turbulence loads criteria in § 25.341(b).
5. Revises § 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 § 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 § 25.361 from “Engine torque” to “Engine and auxiliary power unit torque.”
6. Adds new § 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 § 25.391, “Control surface loads: General,” and § 25.395, “Control system,” to remove references to the ground gust requirements in § 25.415.
8. Revises § 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 § 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 § 25.1585, “Operating procedures,” because it is no longer applicable since that regulation was modified.
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.
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 §§ 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 § 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.
Start Printed 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 § 25.341 (78 FR 37722). On July 16, 2013, the Federal Register published a second correction to one equation in the proposed amendments to § 25.341 (78 FR 42480). The equations in this final rule have not changed from those in the corrected NPRM.
The FAA received two comments. One commenter supported the NPRM and the ongoing international harmonization of certification requirements. The other comment addressed § 25.341 and is discussed below.
Section 25.341(a)(6) uses the term Zmo, which is the maximum operating altitude, in feet, specifically defined in § 25.1527. A commenter noted that the units for the term Zmo are not provided in the current rule. While § 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.
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, § 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 § 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 § 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.
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.”
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.Start Printed Page 73465
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.
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.
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.
(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.
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.Start Printed Page 73466
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
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.
(2) Checked maneuver between VA and VD. Nose-up checked pitching maneuvers must be analyzed in which the positive limit load factor prescribed in § 25.337 is achieved. As a separate condition, nose-down checked pitching maneuvers must be analyzed in which a limit load factor of 0g is achieved. In defining the airplane loads, the flight deck pitch control motions described in paragraphs (c)(2)(i) through (iv) of this section must be used:
δ(t) = δ1 sin(ωt) for 0 ≤ t ≤tmax
(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 § 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.
Start Printed Page 73467
3. Amend § 25.341 by revising paragraphs (a)(5)(i), (a)(6), and (b), and by adding paragraph (c) to read as follows:
Zmo = Maximum operating altitude defined in § 25.1527 (feet).
(1) Except as provided in paragraphs (b)(4) and (5) of this section, the following equation must be used:
PL = PL−1g ±Uσ A
(2) A pair of discrete gusts, one vertical and one lateral. The length of each of these gusts must be independently tuned to the maximum response in accordance with § 25.341(a). The penetration of the airplane in the combined gust field and the phasing of Start Printed Page 73468the 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:
PL-1g = steady 1g load for the condition;
(ii) The gust and turbulence conditions of § 25.341(a) and (b), but assuming 85% of the gust velocities prescribed in § 25.341(a)(4) and 85% of the turbulence intensities prescribed in § 25.341(b)(3).
(2) The vertical gust and turbulence conditions prescribed in § 25.341(a) and (b).
7. Add § 25.362 to read as follows:
(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 Start Printed Page 73469assumed to be static loads, and the hinge moments H must be computed from the formula:
(1) Aileron 0.75 Control column locked or lashed in mid-position.
(2) Aileron * ±0.50 Ailerons at full throw.
(3) Elevator * ±0.75 Elevator full down.
(4) Elevator * ±0.75 Elevator full up.
(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.
(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.
13. Revise 25.1517 to read as follows:
(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.
Issued under authority provided by 49 U.S.C. 106(f) and 44701(a) in Washington, DC, on November 14, 2014.
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).
[FR Doc. 2014-28938 Filed 12-10-14; 8:45 am]