Source: https://www.federalregister.gov/documents/2012/11/28/2012-28768/special-conditions-embraer-sa-model-emb-550-airplane-interaction-of-systems-and-structures
Timestamp: 2018-12-12 15:03:31
Document Index: 408759602

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

Federal Register :: Special Conditions: Embraer S.A., Model EMB-550 Airplane; Interaction of Systems and Structures
A Proposed Rule by the Federal Aviation Administration on 11/28/2012
Send your comments on or before January 14, 2013.
77 FR 70941
70941-70945 (5 pages)
Docket No. FAA-2012-1246
Notice No. 25-12-16-SC
2012-28768
FAA-2012-1246
https://www.federalregister.gov/d/2012-28768 https://www.federalregister.gov/d/2012-28768
This action proposes special conditions for the Embraer S.A. Model EMB-550 airplane. This airplane will have a novel or unusual design feature(s) associated with the interaction of systems and structures. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design feature. These proposed special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.
Send comments identified by docket number [FAA-2012-1246] using any of the following methods:
The Model Embraer EMB-550 airplane is equipped with systems that, directly or as a result of failure or malfunction, affect its structural performance. Current regulations do not take into account loads for the airplane due to the effects of systems on structural performance including normal operation and failure conditions with strength levels related to probability of occurrence. Special conditions are needed to account for these features.
The Embraer S.A. Model EMB-550 airplane is equipped with systems that, directly or as a result of failure or malfunction, affect its structural performance. Current regulations do not take into account loads for the airplane due to the effects of systems on structural performance including normal operation and failure conditions with strength levels related to probability of occurrence. Special conditions are needed to account for these features.
These special conditions define criteria to be used in the assessment of 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 in which partial or complete failure, alone or in combination with other system partial or complete failures, would affect structural performance.
Special conditions have been applied on past airplane programs to require consideration of the effects of systems on structures. The regulatory authorities and industry developed standardized criteria in the Aviation Rulemaking Advisory Committee (ARAC) forum based on the criteria defined in Advisory Circular 25.672, Active Flight Controls, dated November 11, 1983. The ARAC recommendations have 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.
The proposed special conditions are similar to those previously applied to other airplane models and to CS 25.302. The major differences between these proposed special conditions and the current CS 25.302 are as follows:
1. Both these special conditions and CS 25.302 specify the design load conditions to be considered. In paragraphs 2(a)(1) and 2(b)(2)(i) of these special conditions, 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. Paragraph 2(b)(2)(i) of these special conditions include the additional ground-handling conditions of §§ 25.493(d) and 25.503. These conditions are added in case the Embraer S.A. Model EMB-550 airplane has systems that affect braking and pivoting.
3. Both CS 25.302 and paragraph (2)(d) of these special conditions allow consideration of the probability of being in a dispatched configuration when assessing subsequent failures and potential “continuation of flight” loads. However, these special conditions also allow using probability when assessing failures that induce loads at the “time of occurrence,” whereas CS 25.302 does not.
Accordingly, the Federal Aviation Administration (FAA) proposes the following special conditions as part of the type certification basis for Embraer S.A. Model EMB-550 airplanes to address the effects of systems on structures.
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, 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 the specific system.
(a) The criteria defined herein only address the direct structural consequences 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 in which 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 these special conditions.
(b) The following definitions are applicable to these special conditions.
(3) Operational limitations: Limitations, including flight limitations, that can be applied to the airplane operating conditions before dispatch (e.g., fuel, payload, and Master Minimum Equipment List limitations).
(4) Probabilistic terms: The probabilistic terms (i.e., probable, improbable, and extremely improbable) used in these special conditions are the same as those used in § 25.1309.
The following criteria are used in determining the influence of a system and its failure conditions on the airplane structure.
(ii) For residual strength substantiation, the airplane must be able to withstand two-thirds of the ultimate loads defined in paragraph 2(b)(1)(i) of these special conditions. For pressurized cabins, these loads must be combined with the normal operating differential pressure.
(i) The loads derived from the following conditions (or conditions defined by special conditions or equivalent level of safety in lieu of the following special conditions) at speeds up to VC/MC, or the speed limitation prescribed for the remainder of the flight, must be determined:
(C) The limit rolling conditions specified in § 25.349 and the limit unsymmetrical conditions specified in §§ 25.367, 25.427(b), and 25.427(c).
(ii) For static strength substantiation, each part of the structure must be able to withstand the loads in paragraph 2(b)(2)(i) of these special conditions multiplied by a factor of safety depending on the probability of being in this failure state. The factor of safety (FS) is defined in Figure 2.
Note: If Pj is greater than 10−3 per flight hour then a 1.5 factor of safety must be applied to all limit load conditions specified in Subpart C.
(iii) For residual strength substantiation, the airplane must be able to withstand two-thirds of the ultimate loads defined in paragraph 2(b)(2)(ii) of the special conditions. For pressurized cabins, these loads must be combined with the normal operating differential pressure.
Note: If Pj is greater than 10−3 per flight hour, then the flutter clearance speed must not be less than V″.
(1) The system must be checked for failure conditions, not extremely improbable, that degrade the structural capability below the level required by 14 CFR part 25 or significantly reduce the reliability of the remaining system. As far as reasonably practicable, the flightcrew must be made aware of these failures before flight. Certain elements of the control system, such as mechanical and hydraulic components, may use special periodic inspections, and electronic components may use daily checks, in lieu of detection and indication systems to achieve the objective of this requirement. These certification maintenance requirements must be limited to components that are not readily detectable by normal detection and indication systems and where service history shows that inspections will provide an adequate level of safety.
(2) The existence of any failure condition, not extremely improbable, during flight that could significantly affect the structural capability of the airplane and for which the associated reduction in airworthiness can be minimized by suitable flight limitations, must be signaled to the flightcrew. For example, failure conditions that result in a factor of safety between the airplane strength and the loads of Subpart C below 1.25, or flutter margins below V″, must be signaled to the flightcrew during flight.
(d) Dispatch with known failure conditions. If the airplane is to be dispatched in a known system failure condition that affects structural performance, or affects the reliability of the remaining system to maintain structural performance, then the provisions of these special conditions must be met, including the provisions of paragraph 2(a) for the dispatched condition, and paragraph 2(b) for subsequent failures. Expected operational limitations may be taken into account in establishing Pj as the probability of failure occurrence for determining the safety margin in Figure 1 of these special conditions. Flight limitations and expected operational limitations may be taken into account in establishing Qj as the combined probability of being in the dispatched failure condition and the subsequent failure condition for the safety margins in Figures 2 and 3 of these special conditions. These limitations must be such that the probability of being in this combined failure state and then subsequently encountering limit load conditions is extremely improbable. No reduction in these safety margins is allowed if the subsequent system failure rate is greater than 10−3 per hour.