E9-20697. Special Conditions: Alenia Aeronautica Model C-27J Airplane; Interaction of Systems and Structures

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Final special conditions.

SUMMARY:

These special conditions are issued for the Alenia Model C-27J airplane. This airplane will have novel or unusual design features when compared to the state of technology described in the airworthiness standards for transport-category airplanes. These special conditions pertain to the effects of novel or unusual design features such as effects on the structural performance of the airplane.

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.

DATES:

Effective Date: September 28, 2009.

FOR FURTHER INFORMATION CONTACT:

Holly Thorson, FAA, International Branch, ANM-116, Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone [phone], facsimile [phone].

SUPPLEMENTARY INFORMATION:

Background

On March 27, 2006, the European Aviation Safety Agency (EASA) forwarded to the FAA an application from Alenia Aeronautica of Torino, Italy, for U.S. type certification of a twin-engine commercial transport designated as the Alenia model C-27J. The Alenia model C-27J is a twin-turbopropeller, cargo-transport aircraft with a maximum takeoff weight of 67,240 pounds.

Type Certification Basis

Under the provisions of Title 14, Code of Federal Regulations (14 CFR) 21.17 and the bilateral agreement between the U.S. and Italy, Alenia Aeronautica must show that the Alenia model C-27J meets the applicable provisions of 14 CFR part 25, as amended by Amendments 25-1 through 25-87. Alenia also elects to comply with Amendment 25-122, effective September 5, 2007, for § 25.1317.

If the Administrator finds that existing airworthiness regulations do not adequately or appropriately address safety standards for the Alenia model C-27J due to a novel or unusual design feature, we prescribe special conditions under provisions of § 21.16.

In addition to the applicable airworthiness regulations and special conditions, the Alenia model C-27J 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. In addition, the FAA must issue a finding of regulatory adequacy pursuant to § 611 of Public Law 92-574, the “Noise Control Act of 1972.”

The FAA issues special conditions, as defined in 14 CFR 11.19, in accordance with § 11.38, and they become part of the type-certification basis under § 21.17(a)(2).

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, the special conditions also apply to the other model under § 21.101.

Novel or Unusual Design Features

The Alenia model C-27J incorporates several novel or unusual design features. Because of rapid improvements in airplane technology, the existing airworthiness regulations do not adequately or appropriately address safety standards for these design features. These special conditions for the Alenia model C-27J 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.

These special conditions were derived initially from standardized requirements developed by the Aviation Rulemaking Advisory Committee (ARAC), comprised of representatives of the FAA, Europe's Joint Aviation Authorities (JAA), now replaced by the European Aviation Safety Agency (EASA), and industry. From the initial proposal, the JAA proposed these special conditions in Notice of Proposed Amendment (NPA) 25C-199. When Ente Nazionale per l'Aviazione Civile (ENAC) certified the Alenia model C-27J they applied NPA 25C-199, issued July 3, 1997.

Discussion

The Alenia model C-27J is equipped with 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 represent a novel and unusual feature when compared to the technology described in the current airworthiness standards. Special conditions are needed to require consideration of the effects of systems on the structural capability and aeroelastic stability of the airplane, in both the normal and the failed states.

These special conditions require that the airplane meet the structural requirements of subparts C and D of part 25 when the airplane systems are fully operative. These special conditions also require that the airplane meet these requirements taking into consideration failure conditions. In some cases, reduced margins are allowed for failure conditions based on system reliability.

Discussion of Comments

Notice of proposed special conditions no. 25-09-01-SC for the Alenia model C-27J airplane was published in the Federal Register on May 4, 2009. No comments were received, and the special conditions are adopted as proposed.

Applicability

As discussed above, these special conditions are applicable to the Alenia model C-27J. Should Alenia apply at a later date for a change to the type certificate to include another model incorporating the same novel or unusual design features, these special conditions apply to that model as well.

Conclusion

This action affects only certain novel or unusual design features of the Alenia model C-27J. It is not a rule of general applicability, and it affects only the applicant that applied to the FAA for approval of these features on the airplane.

List of Subjects in 14 CFR Part 25

• Aircraft
• Aviation safety
• Reporting and recordkeeping requirements

The authority citation for these special conditions is as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Special Conditions

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 the Alenia model C-27J.

1. General

(a) The Alenia model C-27J is equipped with systems that affect the airplane's structural performance either directly or as a result of failure or malfunction. The influence of these systems and their failure conditions must be taken into account when showing compliance with requirements of subparts C and D of Title 14 of the Code of Federal Regulations (14 CFR), part 25. 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, flutter-control 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.

(b) The criteria defined here address only 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 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.

(c) Depending upon the specific characteristics of the airplane, additional studies may be required, that go beyond the criteria provided in these special conditions, 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.

(d) The following definitions are applicable to these special conditions.

Structural Performance

Capability of the airplane to meet the structural requirements of 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” here 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 variables such as gusts or pilot actions, or reduce flutter margins).

2. Effects of Systems on Structures

(a) General. The following criteria determine the influence of a system and its failure conditions on the airplane structure.

(b) 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 conditions 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.

(2) 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 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.

(3) The airplane must meet the aeroelastic-stability requirements of § 25.629.

(c) 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.

(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 (F.S.) 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 (c)(1)(i).

(iii) Freedom from aeroelastic instability must be shown up to the speeds defined in § 25.629(b)(2). For failure conditions that result in speed increases beyond V_C/M_C, freedom from aeroelastic instability must be shown at increased speeds, so that the margins intended by § 25.629(b)(2) are maintained.

(iv) Failures of the system that result in forced structural vibrations (oscillatory failures) must not produce loads that could result in detrimental deformation of primary structure.

(2) For the continuation of the flight. For the airplane in the system-failed state, and considering any appropriate reconfiguration and flight limitations, the following apply:

(i) The loads derived from the following conditions at speeds up to V_C/M_C, or the speed limitation prescribed for the remainder of the flight, must be determined:

(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 subparagraph (2)(i) of this paragraph, 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.

Q_j = (T_j)(P_j)

Where:

T_j = Average time spent in failure condition j (in hours).

P_j = Probability of occurrence of failure mode j (per hour).

Note:

If P_j 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 subparagraph (c)(2)(ii).

(iv) If the loads induced by the failure condition have a significant effect on fatigue or damage tolerance, then their effects must be taken into account.

(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).

V′ = Clearance speed as defined by § 25.629(b)(2).

V″ = Clearance speed as defined by § 25.629(b)(1).

Q_j = (T_j)(P_j)

Where:

T_j = Average time spent in failure condition j (in hours).

P_j = Probability of occurrence of failure mode j (per hour).

Note:

If P_j is greater than 10⁻³ per 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).

(3) Consideration of certain failure conditions may be required by other subparts 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.

(d) 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 that significantly reduce the reliability of the remaining system. To the extent practicable, these failures must be detected and annunciated to the flight crew 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 warning systems, to achieve the objective of this requirement. These certification-maintenance requirements must be limited to components that are not readily detectable by normal warning systems, and where service history shows that inspections 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 flight crew. 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 crew during flight.

(e) 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 § 25.302 must be met for the dispatched condition and for subsequent failures. Flight limitations and expected operational limitations may be taken into account in establishing Q_j 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.

Issued in Renton, Washington, on August 20, 2009.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.