Source: https://www.federalregister.gov/documents/2013/12/20/2013-30235/special-conditions-airbus-a350-900-series-airplane-interaction-of-systems-and-structures
Timestamp: 2018-08-16 22:16:08
Document Index: 310434908

Matched Legal Cases: ['art 34', 'art 36', '§\u2009611', '§\u200925', 'art 25', '§\u200925', '§\u200925', 'art 25']

Federal Register :: Special Conditions: Airbus, A350-900 Series Airplane; Interaction of Systems and Structures
The effective date of these special conditions is December 20, 2013. We must receive your comments by February 3, 2014.
76980-76984 (5 pages)
Docket No. FAA-2013-0894
Notice No.25-13-16-SC
https://www.federalregister.gov/d/2013-30235 https://www.federalregister.gov/d/2013-30235
Send comments identified by docket number FAA-2013-0894 using any of the following methods:
We will consider all comments we receive by 45 days after publication of these special conditions in the Federal Register. We may change these special conditions based on the comments we receive.
Special conditions have been applied on past airplane programs in order to require consideration of the effects of systems on structures. The regulatory authorities and industry developed standardized criteria in the Aviation Start Printed Page 76981Rulemaking Advisory Committee (ARAC) forum based on the criteria defined in Advisory Circular 25.672, dated November 11, 1983. The ARAC recommendation has been incorporated in European Aviation Safety Agency (EASA) Certification Specifications (CS) 25.302 and CS 25 Appendix K. FAA rulemaking on this subject is not complete, thus the need for the special conditions.
In addition to the applicable airworthiness regulations and special conditions, the Model A350-900 series must comply with the fuel vent and exhaust emission requirements of 14 CFR part 34 and the noise certification requirements of 14 CFR part 36, and the FAA must issue a finding of regulatory adequacy under § 611 of Public Law 92-574, the “Noise Control Act of 1972.”
The Airbus Model A350-900 series will incorporate the following novel or unusual design features: Systems that affect the airplane's structural performance, either directly or as a result of failure or malfunction. That is, the airplane's systems affect how it responds in maneuver and gust conditions, and thereby affect is structural capability. These systems may also affect the aeroelastic stability of the airplane. Such systems include flight control systems, autopilots, stability augmentation systems, load alleviation systems, and fuel management systems. These systems represent novel and unusual features when compared to the technology envisioned in the current airworthiness standards.
Airbus A350 series airplanes are equipped with systems that directly or as a result of failure or malfunction, affect their structural performance. Current regulations do not take into account the effects of systems on structural performance including normal operation and failure conditions. Special conditions are needed to account for these features.
These special conditions define criteria for assessing the effects of these systems on structures. The general approach of accounting for the effect of system failures on structural performance would be extended to include any system whose partial or complete failure, alone or in combination with other system partial or complete failures, would affect structural performance.
The proposed special conditions are similar to those previously applied to other airplane models and to CS 25.302. The major differences between the proposed special conditions and the current CS 25.302 are as follows:
1. Both the special conditions and CS 25.302 specify the design load conditions to be considered. In paragraphs e.(1) and f.(2)(i), the special conditions clarify that, in some cases, different load conditions are to be considered due to other special conditions or equivalent level of safety findings.
2. The special conditions include the additional ground handling conditions of Title 14 Code of Federal Regulations (14 CFR) §§ 25.493(d) and 25.503 in paragraph (f)(2)(i). These conditions are needed because the A350 has systems that affect braking and pivoting.
3. Both the special condition (see paragraph (h) below) and CS 25.302 allow consideration of the probability of being in a dispatched configuration when assessing subsequent failures and potential “continuation of flight” loads. The special conditions, however, also allow using probability when assessing failures that induce loads at the “time of occurrence,” whereas CS 25.302 does not.
For airplanes equipped with systems that affect structural performance, either directly or as a result of a failure or malfunction, the influence of these systems and their failure conditions must be taken into account when showing compliance with the requirements of Title 14 Code of Federal Regulations (14 CFR) part 25 subparts C and D.
The following criteria must be used for showing compliance with these special conditions for airplanes equipped with flight control systems, autopilots, stability augmentation systems, load alleviation systems, flutter control systems, fuel management systems, and other systems that either directly or as a result of failure or malfunction affect structural performance. If these special conditions are used for other systems, it may be necessary to adapt the criteria to that specific system.
(a) The criteria defined herein only address the direct structural Start Printed Page 76982consequences of the system responses and performances and cannot be considered in isolation but should be included in the overall safety evaluation of the airplane. These criteria may in some instances duplicate standards already established for this evaluation. These criteria are only applicable to structure whose failure could prevent continued safe flight and landing. Specific criteria that define acceptable limits on handling characteristics or stability requirements when operating in the system degraded or inoperative mode are not provided in this special condition.
(4) Probabilistic terms: The probabilistic terms (probable, improbable, extremely improbable) used in this special condition are the same as those used in § 25.1309.
(5) Failure condition: The term failure condition is the same as that used in § 25.1309, however this special condition applies only to system failure conditions that affect the structural performance of the airplane (e.g., system failure conditions that induce loads, change the response of the airplane to inputs such as gusts or pilot actions, or lower flutter margins).
(ii) For residual strength substantiation, the airplane must be able to withstand two thirds of the ultimate loads defined in subparagraph (f)(1)(i). For pressurized cabins, these loads must be combined with the normal operating differential pressure.
(2) For the continuation of the flight. For the airplane, in the system failed state and considering any appropriate reconfiguration and flight limitations, the following apply:Start Printed Page 76983
(iii) For residual strength substantiation, the airplane must be able to withstand two thirds of the ultimate loads defined in paragraph (f)(2)(ii) of the special condition. For pressurized cabins, these loads must be combined with the normal operating differential pressure.
(3) Consideration of certain failure conditions may be required by other sections of 14 CFR part 25 regardless of calculated system reliability. Where analysis shows the probability of these failure conditions to be less than 10−9, criteria other than those specified in this paragraph may be used for structural substantiation to show continued safe flight and landing.Start Printed Page 76984
[FR Doc. 2013-30235 Filed 12-19-13; 8:45 am]