[491 0-13] 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No. FAA-2013-0897; Special Conditions No. 25-523-SC] 

Special Conditions: Airbus Model A350-900 airplane; transient engine-failure loads. 

AGENCY: Federal Aviation Administration (FAA), DOT. 

ACTION: Final special conditions. 

SUMMARY: These special conditions are issued for Airbus Model A350-900 airplanes. These 

airplanes will have a novel or unusual design feature associated with the new generation of highbypass engines and the potential loads resulting from extreme engine-failure conditions. 

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. 

EFFECTIVE DATE: September 8, 2014. 

FOR FURTHER INFORMATION CONTACT: Todd Martin, FAA, Airframe and Cabin 

Safety Branch, ANM-115, Transport Airplane Directorate, Aircraft Certification Service, 1601 

Lind Avenue SW., Renton, Washington, 98057-3356; telephone (425) 227-1 178; facsimile (425) 

227-1320. 
SUPPLEMENTARY INFORMATION: 

Background 

On August 25, 2008, Airbus applied for a type certificate for their new Model A350-900 

airplane. Later, Airbus requested, and the FAA approved, an extension to the application for 

FAA type certification to November 15,2009. The Model A350-900 airplane has a conventional 

layout with twin wing-mounted Rolls-Royce Trent XWB engines. It features a twin-aisle, 

9-abreast, economy-class layout, and accommodates side-by-side placement of LD-3 containers 

in the cargo compartment. The basic Model A350-900 airplane configuration accommodates 315 

passengers in a standard two-class atTangement. The design cruise speed is Mach 0.85 with a 

maximum take-off weight of 602,000 lbs. 

The existing regulations are inadequate because the new, large-bypass fan engines of the 

Model A350-900 airplanes can cause more damage in a failure event than could the previous 

engines. To maintain the level of safety envisioned by Title 14, Code of Federal Regulations 

( 14 CFR) 25.61 (b), more comprehensive criteria are needed for the new generation of highbypass engines. The more severe events resulting from extreme engine-failure conditions would 

be treated as dynamic-load conditions. The special conditions would distinguish between the 

more common engine-failure events and those rare events resulting from structural failures. The 

more common events would continue to be treated as static torque-limit load conditions. The 

severe events would be considered ultimate loads, and include all transient loads associated with 

the event. An additional safety factor would be applied to the more critical airframe supporting 

structure. 

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Type Certification Basis 

Under 14 CFR 21.17, Airbus must show that the Model A350-900 airplane meets the 

applicable provisions of 14 CFR part 25, as amended by Amendments 25-1 through 25-129. 

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 Model A350-900 airplane 

airplane because of a novel or unusual design feature, special conditions are prescribed under 

§ 21.16. 

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 would also apply to 

the other model under § 21.1 0 1. 

In addition to the applicable airworthiness regulations and special conditions, the Model 

A350-900 airplane 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. The FAA must issue 

a finding of regulatory adequacy under § 611 of Public Law 92-574, the "Noise Control Act of 

1972." 

The FAA issues special conditions, as defined in 14 CFR 11.19, under§ 11.38, and they 

become part of the type-certification basis under§ 21.17(a)(2). 

Novel or Unusual Design Features 

The Model A350-900 airplane will incorporate the following novel or unusual design 

features: engines with large-bypass fans capable of producing much higher failure loads than 

previous engines. The Model A350-900 airplane will therefore require additional dynamic-load 

analyses to assess the most severe engine-failure events. The loads resulting from these 

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conditions would be considered as ultimate loads, with an additional safety factor applied to the 

airframe supporting structure. 

Discussion 

The size, configuration, and failure modes of jet engines has changed considerably from 

those envisioned by 14 CFR 25.361 (b) when the engine-seizure requirement was first adopted. 

Engines have become larger and are now designed with large-bypass fans capable of producing 

much higher failure loads. Relative to the engine configurations that existed when the rule was 

developed in 1957, the present generation of engines are sufficiently different and novel to 

justify special conditions for Model A350-900 airplanes. Service history has shown that the 

engine-failure events that tend to cause the most severe loads are fan-blade failures, and these 

events occur much less frequently than the typical " limit" load condition. 

The regulatory authorities and industry developed a standardized requirement in the 

Aviation Rulemaking Advisory Committee (ARAC) forum. The technical aspects ofthis 

requirement have been agreed upon and have been accepted by the ARAC Loads and Dynamics 

Harmonization Working Group. These special conditions reflect the ARAC recommendation and 

are essentially harmonized with the corresponding European Aviation Safety Agency (EASA) 

Certification Specifications (CS) 25. In addition, the ARAC recommendation includes 

corresponding advisory material that is incorporated in CS-25. This advisory material is 

considered an acceptable means of compliance to the special conditions. 

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 

airw01ihiness standards. 

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Discussion of Comments 

Notice of proposed special conditions no. 25-13-29-SC for Airbus Model A350-900 

airplanes was published in the Federal Register on November 12, 2013 (78 FR 67323). No 

substantive comments were received, and the special conditions are adopted as proposed. 

Applicability 

As discussed above, these special conditions apply to the Airbus Model A350-900 

airplanes. Should Airbus apply later for a change to the type certificate to include another model 

incorporating the same novel or unusual design feature, the special conditions would apply to 

that model as well. 

Conclusion 

This action affects only certain novel or unusual design features on the Model A350-900 

airplanes. It is not a rule of general applicability. 

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 Airbus Model 

A350-900 airplanes. 

In lieu of§ 25.36l(b), the following special conditions apply: 

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1. For turbine-engine installations, the engine mounts, pylons, and adjacent supporting 

airframe structure must be designed to withstand lg level flight loads acting 

simultaneously with the maximum limit torque loads imposed by each of the following: 

a. sudden engine deceleration due to a malfunction that could result in a temporary 

loss of power or thrust, and 

b. the maximum acceleration ofthe engine. 

2. For auxiliary power-unit installations, the power-unit mounts and adjacent supporting 

airframe structure must be designed to withstand lg level flight loads acting 

simultaneously with the maximum limit torque loads imposed by each of the following: 

a. sudden auxiliary power-unit deceleration due to malfunction or structural failure , 

and 

b. the maximum acceleration of the power unit. 

3. For engine-supporting structure, an ultimate loading condition must be considered that 

combines 1 g flight loads with the transient dynamic loads resulting from: 

a. the loss of any fan, compressor, or turbine blade, and separately 

b. where applicable to a specific engine design, any other engine structural failure 

that results in higher loads. 

4. The ultimate loads developed from the conditions specified in special conditions 3.a. and 

3.b. are to be multiplied by a factor of 1.0 when applied to engine mounts and pylons, and 

multiplied by a factor of 1.25 when applied to adjacent supporting airframe structure. 

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5. The airplane must be capable of continued safe flight considering the aerodynamic effects 

on controllability due to any permanent deformation that results from the conditions 

specified in special condition 3. 

Issued in Renton, Washington, on 'JUl 15 2014 

John P. Piccola, Jr. 

Acting Manager, Transport Airplane Directorate 

Aircraft Certification Service 

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