Source: https://www.federalregister.gov/documents/2016/09/01/2016-21122/special-conditions-bombardier-inc-model-bd-700-2a12-and-bd-700-2a13-airplanes-interactions-of
Timestamp: 2017-10-19 17:08:41
Document Index: 794069483

Matched Legal Cases: ['art 25', '§\u200921', '§\u200925', 'art 25', 'art 25', 'art 25']

Federal Register :: Special Conditions: Bombardier Inc., Model BD-700-2A12 and BD-700-2A13 Airplanes; Interactions of Systems and Structures
Special Conditions: Bombardier Inc., Model BD-700-2A12 and BD-700-2A13 Airplanes; Interactions of Systems and Structures
60236-60240 (5 pages)
Docket No. FAA-2016-4138
Special Conditions No. 25-635-SC
FAA-2016-4138
https://www.federalregister.gov/d/2016-21122 https://www.federalregister.gov/d/2016-21122
These special conditions are issued for the Bombardier Inc. (Bombardier) Model BD-700-2A12 and BD-700-2A13 airplanes. These airplanes will have novel or unusual features when compared to the state of technology envisioned in the airworthiness standards for transport-category airplanes. These design features include systems that, directly or as a result of failure or malfunction, affect structural performance. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for these design features. These 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-2016-4138 using any of the following methods:
If the Administrator finds that the applicable airworthiness regulations (i.e., 14 CFR part 25) do not contain adequate or appropriate safety standards for the BD-700-2A12 and BD-700-2A13 airplanes because of a novel or unusual design feature, special conditions are prescribed under the provisions of § 21.16.Start Printed Page 60237
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 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.
The flight-control system of the Model BD-700-2A12 and BD-700-2A13 airplanes will consist of a full-authority fly-by-wire system with Normal and Direct modes of operation. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design feature. These 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. Special conditions have been applied on past airplane programs, with similar systems, to require consideration of the effects of those 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 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 special conditions.
These special conditions are similar to those previously applied to other airplane models and to EASA CS 25.302. Transport Canada Civil Aviation (TCCA) plans to include CS 25.302 in the Model BD-700-2A12 and BD-700-2A13 airplanes' Canadian certification basis. The differences between these FAA special conditions and the current CS 25.302, which the FAA regards as minor, are shown below. Both these special conditions and CS 25.302:
Specify the design load conditions to be considered. Special conditions 2(a)(i) and 2(b)(ii)(1) of these 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.
allow consideration of the probability of being in a dispatched configuration when assessing subsequent failures and potential “continuation of flight” loads (see special condition 2(d), below). These 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 FAA provision is relieving as compared to CS 25.302.
The FAA chooses to preserve these minor differences and go forward with this version of the special conditions.
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 Start Printed Page 60238acceptable limits on handling characteristics or stability requirements, when operating in the system-degraded or inoperative mode, are not provided in these special 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.
2. The limit gust and turbulence conditions specified in §§ 25.341 and 25.345.Start Printed Page 60239
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.
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.
b. 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.
4. Failure indications. For system-failure detection and indication, the following apply:
a. 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 that 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 Start Printed Page 60240daily 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.
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 14 CFR 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 reliability 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 hour.
[FR Doc. 2016-21122 Filed 8-31-16; 8:45 am]