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Final Special Condition

Federal Register Information

Header Information

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No. NM398; Special Conditions No. 25-390-SC]

Special Conditions: Alenia Aeronautica Model C-27J Airplane; Interaction of 

Systems and Structures 

Preamble Information

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 transportcategory 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. 

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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 (425) 227-

1357, facsimile (425) 227-1149. 

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 Sec. 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 Sec. 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 Sec. 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 Sec. 11.38, and they become part of the type- certification basis under Sec. 

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 Sec. 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 

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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. 

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Final Special Conditions Information

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, loadalleviation 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 

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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 Sec. 25.1309. 

Failure Condition 

The term ``failure condition'' here is the same as that used in Sec. 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 Sec. 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. 

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(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 Sec. 25.629(b)(2). For failure conditions that result in speed increases beyond 

VC/MC, freedom from aeroelastic instability must be shown at increased speeds, 

so that the margins intended by Sec. 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 VC/MC, or the 

speed limitation prescribed for the remainder of the flight, must be determined: 

(A) The limit-symmetrical-maneuvering conditions specified in Sec. 25.331 and in 

Sec. 25.345. 

(B) The limit-gust-and-turbulence conditions specified in Sec. 25.341 and in Sec. 

25.345. 

(C) The limit-rolling conditions specified in Sec. 25.349, and the limitunsymmetrical conditions specified in Sec. 25.367 and Sec. 25.427(b) and (c). 

(D) The limit-yaw-maneuvering conditions specified in Sec. 25.351. 

(E) The limit-ground-loading conditions specified in Sec. 25.473 and Sec. 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. 

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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 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 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 

Sec. 25.629(b). 

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V' = Clearance speed as defined by Sec. 25.629(b)(2). 

V'' = Clearance speed as defined by Sec. 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 Pj 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 Sec. 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 Sec. 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 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. 

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Footer Information

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

Ali Bahrami, 

Manager, Transport Airplane Directorate, 

Aircraft Certification Service. 

[FR Doc. E9-20697 Filed 8-27-09; 8:45 am] 

BILLING CODE 4910-13-P 

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