Source: http://thefederalregister.com/2012/10/18/2012-25604.html
Timestamp: 2018-02-20 13:16:25
Document Index: 373762183

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

[Docket No. FAA-2012-1118; Special Conditions No. 25-469-SC]
Special Conditions: Airbus Model A318, A319, A320, and A321 Series Airplanes; Interaction of Systems and Structures
SUMMARY: These special conditions are issued for the Airbus Model A318, A319, and A320 series airplanes with modification 160500 and Model A321 series airplanes with modification 160023 (Sharklet). These airplanes will have novel or unusual design features when compared to the state of technology envisioned in the airworthiness standards for transport category airplanes. The design features are associated with the systems that affect the structural performance of the airplane. 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.
FAA issued special conditions 25-ANM-23, effective December 15, 1988, originally applicable to Airbus Model A320 series airplanes and later to the Model A318, A319, and A321 series airplanes. Those special conditions included requirements for interactions of systems and structures. Airbus requested, and FAA agrees, that these special conditions be updated for the Airbus Model A318, A319, and A320 series airplanes with modification 160500 and Model A321 series airplanes with modification 160023 (Sharklet) and later derivatives to be consistent with the latest European Aviation Safety Standards (EASA) standards and the latest versions of the FAA special conditions issued on this subject.
Special conditions are initially applicable to the model for which they are issued. Should the type certificate for that model be amended later toinclude any other model that incorporates the same novel or unusual design feature, or should any other model already included on the same type certificate be modified to incorporate the same novel or unusual design feature, the special conditions would also apply to the other model.
The Airbus Model A318, A319, and A320 series airplanes with modification 160500 and Model A321 series airplanes with modification 160023 (Sharklet) will incorporate the following novel or unusual design features: Systems that, directly or as a result of failure or malfunction, affect structural performance. These systems include flight control systems, autopilots, stability augmentation systems, load alleviation systems, fuel management systems, and other sytems.
These airplanes are 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 aircraft due to the effects of systems on structural performance including normal operation and failure conditions with strength levels related to probability of occurrence. These special conditions define criteria to be used in the assessment of the effects of these systems on structures.
As discussed above, these special conditions are applicable to the Airbus Model A318, A319, A320 series airplanes with modification 160500 and Model A321 series airplanes with modification 160023 (Sharklet). Should Airbus apply at a later date for a change to the type certificate to include another model incorporating the same novel or unusual design features, the special conditions would apply to that model as well.
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 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 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 these special conditions.
(b) Depending upon the specific characteristics of the airplane, additional studies may be required that go beyond the criteria provided in these special conditions in order to demonstrate the capability of the airplane in meeting other realistic conditions such as alternative gust or maneuver descriptions for an airplane equipped with a load alleviation system.
(c) The following definitions are applicable to these special conditions:
Structural performance:Capability of the airplane to meet the structural requirements of 14 CFR part 25.
Flight limitations:Limitations that can be applied to the airplane flight conditions following an in-flight occurrence and that are included in the flight manual (e.g., speed limitations, avoidance of severe weather conditions, etc.).
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).
Probabilistic terms:The probabilistic terms (probable, improbable, extremely improbable) used in these special conditions are the same as those used in § 25.1309.
Failure condition:The term failure condition 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).
(a)System fully operative.With the system fully operative, the following apply:
(1) Limit loads must be derived in all normal operating configurations of the system from all the limit conditionsspecified in Subpart C (or defined by special condition or 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.
(3) The airplane must meet the aeroelastic stability requirements of § 25.629.
(b)System in the failure condition.For any system failure condition not shown to be extremely improbable, the following apply:
(1) At the time of occurrence, starting from 1-g level flight conditions, a realistic scenario, including pilot corrective actions, must be established to determine the loads occurring at the time of failure and immediately after failure.
ER18OC12.000
(ii) For residual strength substantiation, the airplane must be able to withstand two thirds of the ultimate loads defined in subparagraph 2(b)(1)(i). For pressurized cabins, these loads must be combined with the normal operating differential pressure.
(iii) Freedom from aeroelastic instability must be shown up to the speeds defined in § 25.629(b)(2). For failure conditions that result in speeds beyond VC/MC, freedom from aeroelastic instability must be shown to increased speeds, so that the margins intended by § 25.629(b)(2) are maintained.
(A) The limit symmetrical maneuvering conditions specified in § 25.331 and in § 25.345.
(B) The limit gust and turbulence conditions specified in § 25.341 and in § 25.345.
(C) The limit rolling conditions specified in § 25.349 and the limit unsymmetrical conditions specified in § 25.367 and § 25.427(b) and (c).
(D) The limit yaw maneuvering conditions specified in § 25.351.
(E) The limit ground loading conditions specified in §§ 25.473 and 25.491.
(ii) For static strength substantiation, each part of the structure must be able to withstand the loads in paragraph 2(b)(2)(i) of the special conditions 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.
ER18OC12.001 Qj= (Tj)(Pj) Where: Tj= Average time spent in failure condition j (in hours) Pj= Probability of occurrence of failure mode j (per hour) Note:
If Pjis greater than10−3per 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.
(v) Freedom from aeroelastic instability must be shown up to a speed determined from Figure 3. Flutter clearance speeds V′ and V″ may be based on the speed limitation specified for the remainder of the flight using the margins defined by § 25.629(b).
ER18OC12.002 V′ = Clearance speed as defined by § 25.629(b)(2). V″ = Clearance speed as defined by § 25.629(b)(1). Qj= (Tj)(Pj) where: Tj= Average time spent in failure condition j (in hours) Pj= Probability of occurrence of failure mode j (per hour) Note:
If Pjis greater than 10−3per flight hour, then the flutter clearance speed must not be less than V″.
(vi) Freedom from aeroelastic instability must also be shown up to V′ in Figure 3 above, for any probable system failure condition combined with any damage required or selected for investigation by § 25.571(b).
(c)Failure indications.For system failure detection and indication, the following apply:
(d)Dispatch with known failure conditions.If the airplane is to bedispatched 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 Pjas 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 Qjas 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 10−3per hour.