[Federal Register Volume 79, Number 152 (Thursday, August 7, 2014)]
[Rules and Regulations]
From the Federal Register Online via the Government Publishing 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
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-
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
The normal load-factor limit on Airbus Model A350-900 airplanes is
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
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.
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
Low stick-force/displacement gradients, and
Smooth transition from pilot elevator control to limit
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
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.
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.
This action affects only certain novel or unusual design features
on the Airbus Model A350-900 airplanes. It is not a rule of general
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
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
(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
(b) 2.0g for the EFCS normal state with the high-lift devices
(2) The negative limiting load factor must be equal to or more
(a) Minus 1.0g for the EFCS normal state with the high-lift devices
(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
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
[FR Doc. 2014-18660 Filed 8-6-14; 8:45 am]
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