Document ID: FAA-2013-0905-0002
Agency: faa
Document Type: Rule
Title: Special Conditions: Airbus Model A350-900 Airplane; Flight-Envelope Protection, Normal Load-Factor (G) Limiting
Posted Date: 2014-08-07T04:00Z

[Federal Register Volume 79, Number 152 (Thursday, August 7, 2014)]
[Rules and Regulations]
[Pages 46171-46173]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2014-18660]

-----------------------------------------------------------------------

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.

DATES: 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

[[Page 46172]]

unique in that traditional airplanes with conventional flight-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.
    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 Sec.  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 Sec.  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 section 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 Sec.  11.38, and they become part of the type-certification basis 
under Sec.  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, 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 VMO/MMO. At speeds 
greater than VMO and up to VDF, 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 stick-
displacement 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.

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 Sec.  25.143(a), and in the absence of 
other limiting factors, the following special conditions are issued as 
part of the type-certification 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 VMO/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 1.0g for the EFCS normal state with the high-lift devices 
retracted.
    (b) 0.0g 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, 0g is readily achievable or alternatively, a 
satisfactory trajectory change is readily achievable at operational 
speeds (from VLS to maximum speed--10 knots). VLS 
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-

[[Page 46173]]

speed amber band, and is the lower end of the normal flight envelope. 
The formula (maximum speed--10 knots) is to cover typical margin from 
VMO/MMO to cruise speeds, and typical margin from 
VFE to standard speed in high lift configurations.

    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.

    Issued in Renton, Washington, on July 15, 2014.
John P. Piccola, Jr.,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2014-18660 Filed 8-6-14; 8:45 am]
BILLING CODE 4910-13-P