Source: https://www.federalregister.gov/documents/2012/02/10/2012-3077/special-conditions-learjet-inc-learjet-model-lj-200-1a10-interaction-of-systems-and-structures
Timestamp: 2018-03-21 17:04:46
Document Index: 243722433

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

Federal Register :: Special Conditions: Learjet Inc., Learjet Model LJ-200-1A10; Interaction of Systems and Structures
Special Conditions: Learjet Inc., Learjet Model LJ-200-1A10; Interaction of Systems and Structures
A Rule by the Federal Aviation Administration on 02/10/2012
The effective date of these special conditions is February 3, 2012. We must receive your comments by March 26, 2012.
77 FR 6945
6945-6949 (5 pages)
Docket No. FAA-2012-0154
Special Conditions No. 25-457-SC
FAA-2012-0154
2. Effects of Systems on Structures
https://www.federalregister.gov/d/2012-3077 https://www.federalregister.gov/d/2012-3077
These special conditions are issued for the Learjet Model LJ-200-1A10 airplane. This airplane will have novel or unusual design features associated with 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-2012-0154 using any of the following methods:
Docket: Background documents or comments received may be read at http://www.regulations.gov/at any time. Follow the online instructions for accessing the docket or go to the Docket Operations in Room W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue SE., Washington, DC between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.
The FAA has determined that notice of, and opportunity for public comments on, these special conditions are unnecessary. 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 that good cause exists for making these special conditions effective upon issuance.
On February 9, 2009, Learjet Inc. applied for a type certificate for their new Model LJ-200-1A10 (hereafter referred to as “Model LJ-200”) airplane. The Model LJ-200 is a business class aircraft powered by 2 high bypass turbine engines with an estimated maximum takeoff weight of 36,000 pounds and an interior configuration for up to 10 passengers.
The 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 aircraft due to the effects of system failures on structural performance. 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 whose partial or complete failure, alone or in combination with other system failures, would affect structural performance.
Under the provisions of Title 14, Code of Federal Regulations (14 CFR) 21.17, Learjet Inc. must show that the Model LJ-200 meets the applicable provisions of part 25, as amended by Amendments 25-1 through 25-127 thereto.
Special conditions are initially applicable to the model for which they are issued. Should the type certificate for that model be amended later to include any other model that incorporates the same or similar novel or unusual design feature, these special conditions would also apply to the other model.
In addition to the applicable airworthiness regulations and special conditions, the Model LJ-200 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 pursuant to § 611 of Public Law 92-574, the “Noise Control Act of 1972.”
The Model LJ-200 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 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. Such systems represent novel and unusual features when compared to the technology envisioned in the current airworthiness standards.
These special conditions require that the airplane meet the structural requirements of subparts C and D of 14 CFR part 25 when the airplane systems are fully operative. The special conditions also require that the airplane meet these requirements considering failure conditions. In some cases, reduced margins are allowed for failure conditions based on system reliability.
As discussed above, these special conditions are applicable to the Learjet Model LJ-200-1A10. Should Learjet Inc. 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.
Accordingly, pursuant to the authority delegated to me by the Administrator, the following special conditions are issued as part of the type certification basis for Learjet Model LJ-200-1A10 airplanes.
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 on structural performance 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.
(a) The criteria defined herein only address the direct structural consequences of the system responses and performances. 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 structures 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 to meet 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.
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).
(1) Limit loads must be derived in all normal operating configurations of the system from all the limit conditions specified 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.
(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.
(i) For static strength substantiation, these loads, multiplied by an appropriate factor of safety that is related to the probability of occurrence of the failure, are ultimate loads to be considered for design. The factor of safety is defined in Figure 1.
(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) 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 defined by special condition or 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:
(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 is defined in Figure 2.
(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 these special conditions. For pressurized cabins, these loads must be combined with the normal operating differential pressure.
V1' = Clearance speed as defined by § 25.629(b)(2).
V'' = Clearance speed as defined by § 25.629(b)(1).
(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).’ ”
(3) 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, criteria other than those specified in this paragraph may be used for structural substantiation to show continued safe flight and landing.
(c) Failure indications. For system failure detection and indication, the following apply:
(1) The system must be checked for failure conditions, not extremely improbable, that degrade the structural capability below the level required by part 25 or significantly reduce the reliability of the remaining system. As far as reasonably practicable, the flight crew 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.
(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. 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.
For each system for which these special conditions are applied, the following must be identified for showing compliance:
(a) The system that either directly or as a result of failure or malfunction affects structural performance;
(b) The failure condition of the system and the probability of that failure;
(c) The structure whose performance is affected directly or as a result of failure or malfunction of the system; and,
(d) The loading condition(s) on the structure affected by the system.
Issued in Renton, Washington, on February 3, 2012.
[FR Doc. 2012-3077 Filed 2-9-12; 8:45 am]