[491 0-13] 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No. FAA-2013-0905; Special Conditions No. 25-531-SC] 

Special Conditions: Airbus Model A350-900 airplane; flight-envelope protection, normal 

load-factor (g) limiting. 

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 a flight-control 

system that prevents the pilot from inadvertently or intentionally exceeding the positive or 

negative airplane limit load factor. 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: Joe Jacobsen, FAA, Airplane and Flightcrew 

Interface Branch, ANM-111 , Transport Airplane Directorate, Aircraft Certification Service, 1601 

Lind Avenue SW., Renton, Washington, 98057-3356; telephone (425) 227-2011 ; 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 arrangement. The design cruise speed is Mach 0.85 with a 

maximum take-off weight of 602,000 lbs. 

The normal load-factor limit on Airbus Model A350-900 airplanes is unique in that 

traditional airplanes with conventional ±light-control systems (mechanical linkages) are limited 

in the pitch axis only by the elevator surface area and deflection limit. The elevator-control 

power is normally derived for adequate controllability and maneuverability at the most critical 

longitudinal pitching moment. The result is that traditional airplanes have a significant portion of 

the flight envelope wherein maneuverability in excess of limit structural-design values is 

possible. 

Title 14, Code of Federal Regulations (14 CFR) part 25 does not specify requirements or 

policy for demonstrating maneuver controls that impose any handling-qualities requirements 

beyond the design limit structural loads. Nevertheless, some pilots have become accustomed to 

the availability of this excess maneuver capacity in case of extreme emergency, such as upset 

recoveries or collision avoidance. 

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These special conditions are needed to ensure adequate maneuverability and 

controllability for the Model A350-900 airplane using the Airbus flight-control system. 

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 

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 ce11ificate 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 § 21.101 . 

In addition to the applicable airworthiness regulations and final 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 Airbus Model A350-900 airplane will incorporate the following novel or unusual 

design features: an electronic flight-control system (EFCS), that when operating in its normal 

mode, will prevent airplane pitch attitudes greater than + 30 degrees and less than - 15 degrees, 

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and roll angles greater than plus or minus 67 degrees. In addition, positive spiral stability is 

introduced for roll angles greater than 33 degrees at speeds below V Mo/MMo· At speeds greater 

than VMo and up to VoF, maximum aileron-control force is limited to only 45 degrees maximum 

bank angle. 

Discussion 

Flight-envelope protection that limits normal load-factor (g) limiting is considered novel 

and unusual because the current regulations do not provide standards for maneuverability and 

controllability evaluations for such systems. Special conditions are needed to ensure adequate 

maneuverability and controllability when using this design feature. 

As with previous fly-by-wire airplanes, the FAA has no regulatory or safety reason to 

inhibit the design concept of the Airbus A350 flight-control system with load-factor limiting. 

Pilots accustomed to this control feature may feel more freedom in commanding full stickdisplacement maneuvers because of the following: 

• Knowledge that the limit system will protect the structure, 

• Low stick-force/displacement gradients, and 

• Smooth transition from pilot elevator control to limit control. 

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. 

Discussion of Comments 

Notice of proposed special conditions no. 25-13-28-SC for Airbus Model A350-900 

airplanes was published in the Federal Register on December 17, 2013 (78 FR 76249). No 

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

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Applicability 

As discussed above, these special conditions apply to 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 Airbus 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, to meet the 

intent of adequate maneuverability and controllability required by§ 25.143(a), and in the 

absence of other limiting factors, the following special conditions are issued as part of the typecertification basis for Airbus Model A350-900 airplanes. 

1) The positive limiting load factor must not be less than: 

a) 2.5g for the EFCS normal state with the high-lift devices retracted up to V Mo/MMO· The 

positive limiting load factor may be gradually reduced down to 2.25g above VMo/MMO· 

b) 2.0g for the EFCS normal state with the high-lift devices extended. 

2) The negative limiting load factor must be equal to or more negative than: 

a) Minus l.Og for the EFCS normal state with the high-lift devices retracted. 

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b) O.Og for the EFCS normal state with high-lift devices extended. 

3) Maximum reachable positive load-factor wings level may be limited by flight-control system 

characteristics or flight-envelope protections (other than load-factor protection) provided 

that: 

a) the required values are readily achievable in turns, and 

b) wings-level pitch-up responsiveness is satisfactory. 

4) Maximum achievable negative load factor may be limited by flight-control system 

characteristics or flight-envelope protections (other than load-factor protection) provided 

that: 

a) pitch-down responsiveness is satisfactory 

b) from level flight, Og is readily achievable or alternatively, a satisfactory trajectory change 

is readily achievable at operational speeds (from V LS to maximum speed- 1 0 knots). V LS 

is the lowest speed at which the crew may fly with auto-thrust or auto-pilot engaged. It is 

displayed on primary flight displays as the top of the low-speed amber band, and is the 

lower end of the normal flight envelope. The formula (maximum speed- 1 0 knots) is to 

cover typical margin from V Mo/MMo to cruise speeds, and typical margin fi"om V r:E to 

standard speed in high lift configurations. 

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Note: For the FAA to consider a trajectory change as satisfactory, the applicant should 

propose and justify a pitch rate that provides sufficient maneuvering capability in the most 

critical scenarios. Compliance demonstration with the above requirements may be performed 

without ice accretion on the airframe. 

·--,;;..---:;::i ~l15 2014 

John P. Piccola, Jr. 

Acting Manager, Transport Airplane Directorate 

Aircraft Certification Service 

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