Source: https://www.federalregister.gov/documents/2017/08/04/2017-16415/special-conditions-embraer-sa-model-erj-190-300-airplane-interaction-of-systems-and-structures
Timestamp: 2017-10-22 17:51:37
Document Index: 521747267

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

Federal Register :: Special Conditions: Embraer S.A. Model ERJ 190-300 Airplane; Interaction of Systems and Structures
Special Conditions: Embraer S.A. Model ERJ 190-300 Airplane; Interaction of Systems and Structures
36328-36332 (5 pages)
FAA-2017-0318
https://www.federalregister.gov/d/2017-16415 https://www.federalregister.gov/d/2017-16415
Send comments identified by docket number FAA-2017-0318 using any of the following methods:
In addition, the substance of these special conditions has been subject to the public-comment process in several prior instances with no substantive comments received. The FAA therefore finds it unnecessary to delay the effective date and that good cause exists for making these special conditions effective upon publication in the Federal Register.
Systems that, directly or as a result of failure or malfunction, affect airplane structural performance. That is, the Start Printed Page 36329airplane's systems affect how it responds in maneuver and gust conditions, and thereby affect its 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.
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 (AC) 25.672-1, dated November 15, 1983. The ARAC recommendations have been incorporated in European Aviation Safety Agency (EASA) Certification Specifications (CS) 25.302 and CS 25 Appendix K, which are applicable to Embraer. FAA rulemaking on this subject is not complete, thus the need for the special conditions.
The special conditions are similar to those previously applied to other airplane models and to the requirements of CS 25.302. The major differences between these special conditions and the current CS 25.302 are as follows:
(1) Both the special conditions and CS 25.302 (and by reference Appendix K) specify the design load conditions to be considered. Effects of Systems on Structures, special conditions 2.a. and 3.b.i. clarify that, in some cases, different load conditions are to be considered due to other special conditions or equivalent-level-of-safety findings.
(2) Both the special conditions (see special condition 5, 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.
The substance of these special conditions has been published in the Federal Register for public comment in several prior instances and has been derived without substantive change from those previously issued. It is unlikely that prior public comment would result in a significant change from the substance contained herein. Therefore, the FAA has determined that prior public notice and comment are unnecessary and impracticable, and good cause exists for adopting these special conditions upon publication in the Federal Register. The FAA is requesting comments to allow interested persons to submit views that may not have been submitted in response to the prior opportunities for comment described above.
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 part 25, subparts C and D.
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, the following criteria must be used for showing compliance. If these special conditions are used for other systems, it may be necessary to adapt the criteria to the specific system.
1. The criteria defined herein only address the direct structural consequences of the system responses and performance. They 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 the failure of which 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.
a. Structural performance: Capability of the airplane to meet the structural requirements of part 25.
e. Failure condition: This term is the same as that used in § 25.1309. However, these special conditions apply 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).Start Printed Page 36330
a. Limit loads must be derived in all normal operating configurations of the system from all the limit conditions specified in part 25, subpart C (or defined by special conditions or findings of equivalent level of safety in lieu of those specified in subpart C), taking into account any special behavior of such a system or associated functions, or any effect on the structural performance of the airplane that may occur up to the limit loads. In particular, any significant nonlinearity (rate of displacement of control surface, thresholds, or any other system nonlinearities) must be accounted for in a realistic or conservative way when deriving limit loads from limit conditions.
b. The airplane must meet the strength requirements of part 25 (static strength, residual strength), using the specified factors to derive ultimate loads from the limit loads defined above. The effect of nonlinearities must be investigated beyond limit conditions to ensure that the behavior of the system presents no anomaly compared to the behavior below limit conditions. However, conditions beyond limit conditions need not be considered when it can be shown that the airplane has design features that will not allow it to exceed those limit conditions.
ii. For residual-strength substantiation, the airplane must be able to withstand two thirds of the ultimate loads defined in special condition 3.a.i. For pressurized cabins, these loads must be combined with the normal operating differential pressure.
i. The loads derived from the following conditions (or defined by special conditions or findings of equivalent level of safety in lieu of the following conditions) at speeds up to VC/MC (or the speed limitation prescribed for the remainder of the flight) must be determined:
5. the limit ground-loading conditions specified in §§ 25.473, 25.491, 25.493(d), and 25.503.
ii. For static-strength substantiation, each part of the structure must be able to withstand the loads in special condition 3.b.i., multiplied by a factor of safety depending on the probability of being in this failure state. The factor of safety is defined in Figure 2, below.
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 part 25, subpart C.
iii. For residual-strength substantiation, the airplane must be able to withstand two-thirds of the ultimate loads defined in paragraph 3.b.ii. of these special conditions. For pressurized cabins, these loads must be combined with the normal operating differential pressure.
c. Consideration of certain failure conditions may be required by other sections of part 25 regardless of calculated system reliability. Where analysis shows the probability of these failure conditions to be less than 10−9 per flight hour, criteria other than those specified in this paragraph may be used for structural substantiation to show continued safe flight and landing.
b. 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 part 25, subpart C below 1.25, or flutter margins below V″, must be signaled to the crew during flight.
5. Dispatch with known failure conditions. If the airplane is to be dispatched in a known system-failure condition that affects structural performance, or that affects the Start Printed Page 36332reliability of the remaining system to maintain structural performance, then the provisions of these special conditions must be met, including the provisions of special condition 2 for the dispatched condition, and special condition 3 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. 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. 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 flight hour.
[FR Doc. 2017-16415 Filed 8-3-17; 8:45 am]