Document ID: FAA-2013-1001-0002
Agency: faa
Document Type: Rule
Title: Special Conditions: Airbus Model A350-900 Airplanes; High-Speed Protection System
Posted Date: 2014-08-21T04:00Z

[Federal Register Volume 79, Number 162 (Thursday, August 21, 2014)]
[Rules and Regulations]
[Pages 49427-49429]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2014-19824]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2013-1001; Special Conditions No. 25-535-SC]

Special Conditions: Airbus Model A350-900 Airplanes; High-Speed 
Protection System

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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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 high-speed protection system that limits nose-down 
pilot authority at speeds above VC/MC, and 
prevents the airplane from performing the maneuver required under the 
Code of Federal Regulations. 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 22, 2014.

FOR FURTHER INFORMATION CONTACT: Todd Martin, FAA, Airframe/Cabin 
Safety, ANM-115, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue SW., Renton, Washington 98057-3356; telephone 
(425) 227-1178; facsimile (425) 227-1322.

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 Model A350-900 airplane, like Airbus Model A320, A330, A340 and 
A380 series airplanes, has a high-speed protection system that limits 
nose-down pilot authority at speeds above VC/MC, 
and prevents the airplane from actually performing the maneuver 
required under Sec.  25.335(b)(1). Special conditions are necessary to 
address the Model A350-900 airplane high-speed protection system. These 
special conditions identify various symmetric and non-symmetric 
maneuvers that will ensure that an appropriate design dive speed, 
VD/MD, is established.

Type Certification Basis

    Under Title 14, Code of Federal Regulations (14 CFR) 21.17, Airbus 
must show that the Model A350-900 airplane meets the applicable 
provisions of 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 the provisions of 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 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

    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 Sec.  611 of Public Law 92-574, 
the ``Noise Control Act of 1972.''
    The Airbus Model A350-900 airplane will incorporate the following 
novel or unusual design features:
    A high-speed protection system that limits nose-down pilot 
authority at speeds above VC/MC, and prevents the 
airplane from actually performing the maneuver required under Sec.  
25.335(b)(1). The special conditions identify various symmetric and 
non-symmetric maneuvers that will ensure that an appropriate design 
dive speed, VD/MD, is established.

Discussion

    Section 25.335(b)(1) is an analytical envelope condition originally 
adopted in Part 4b of the Civil Air Regulations to provide an 
acceptable speed margin

[[Page 49428]]

between design cruise speed and design dive speed. Flutter-clearance 
design speeds and airframe design loads are impacted by the design dive 
speed. While the initial condition for the upset specified in the rule 
is 1g level flight, protection is afforded for other inadvertent 
overspeed conditions as well. Section 25.335(b)(1) is intended as a 
conservative enveloping condition for potential overspeed conditions, 
including non-symmetric conditions.
    To establish that potential overspeed conditions are enveloped, 
Airbus should demonstrate that any reduced speed margin, based on the 
high-speed protection system in the Model A350-900 airplane, will not 
be exceeded in inadvertent, or gust-induced, upsets resulting in 
initiation of the dive from non-symmetric attitudes; or that the 
airplane is protected, by the flight-control laws, from getting into 
non-symmetric upset conditions. The special conditions identify various 
symmetric and non-symmetric maneuvers that will ensure that an 
appropriate design dive speed, VD/MD, is 
established.
    These special conditions are in lieu of Sec.  25.335(b)(1). Section 
25.335(b)(2), which also addresses the design dive speed, is applied 
separately (Advisory Circular (AC) 25.335-1A provides an acceptable 
means of compliance to Sec.  25.335(b)(2)). The applicant should 
conduct a demonstration that includes a comprehensive set of 
conditions, as described below.
    Special conditions (3) and (4) indicate that failures of the high-
speed protection system must be improbable and must be annunciated to 
the pilots. If these two criteria are not met, then the probability 
that the established dive speed will be exceeded, and the resulting 
risk to the airplane, is too great. On the other hand, if the high-
speed protection system is known to be inoperative, then dispatch of 
the airplane could be acceptable under an approved minimum-equipment 
list (MEL) containing language similar to special condition (5). 
Dispatch under an MEL would require that appropriate reduced operating 
speeds, VMO/MMO, are provided in the airplane 
flight manual (AFM), and the cockpit display of those reduced speeds, 
as well as the overspeed warning for exceeding those speeds, are 
equivalent to that of the normal airplane with the high-speed 
protection system operative.
    We do not believe that application of the Interaction of Systems 
and Structures special conditions (docket no. FAA-2013-0894), or the 
European Aviation Safety Agency (EASA) Certification Specification (CS) 
25.302, is appropriate in this case because design dive speed is, in 
and of itself, part of the design criteria. Stability and control, 
flight loads, and flutter evaluations all depend on the design dive 
speed. Therefore, a single design dive speed should be established that 
will not be exceeded, taking into account the performance of the high-
speed protection system as well as its failure modes, failure 
indications, and accompanying AFM instructions.
    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. 25-13-35-SC for Airbus 
Model A350-900 airplanes was published in the Federal Register on 
December 24, 2013 (78 FR 77611). 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 at a later date for a change to 
the type certificate to include another airplane series incorporating 
the same novel or unusual design feature, the special conditions would 
apply to that series as well.

Conclusion

    This action affects only certain novel or unusual design features 
on the Airbus Model A350-900 series 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 and 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 series 
airplanes.
    1. In lieu of compliance with Sec.  25.335(b)(1), if the flight-
control system includes functions that act automatically to initiate 
recovery before the end of the 20-second period specified in Sec.  
25.335(b)(1), VD/MD must be determined from the 
greater of the speeds resulting from conditions (a) and (b), below. The 
speed increase occurring in these maneuvers may be calculated if 
reliable or conservative aerodynamic data are used.
    a. From an initial condition of stabilized flight at VC/
MC, the airplane is upset so as to travel a new flight path 
7.5 degrees below the initial path. Control application, up to full 
authority, is made to try to maintain this new flight path. Twenty 
seconds after initiating the upset, manual recovery is made at a load 
factor of 1.5 g (0.5 acceleration increment), or such greater load 
factor that is automatically applied by the system with the pilot's 
pitch control set to neutral. Power, as specified in Sec.  
25.175(b)(1)(iv), is assumed until recovery is initiated, at which time 
power reduction and the use of pilot-controlled drag devices may be 
used.
    b. From a speed below VC/MC, with power to 
maintain stabilized level flight at this speed, the airplane is upset 
so as to accelerate through VC/MC at a flight 
path 15 degrees below the initial path (or at the steepest nose-down 
attitude that the system will permit with full control authority, if 
less than 15 degrees). The pilot's controls may be in the neutral 
position after reaching VC/MC and before recovery 
is initiated. Recovery may be initiated three seconds after operation 
of the high-speed warning system by application of a load of 1.5g (0.5 
acceleration increment), or such greater load factor that is 
automatically applied by the system with the pilot's pitch control set 
to neutral. Power may be reduced simultaneously. All other means of 
decelerating the airplane, the use of which is authorized up to the 
highest speed reached in the maneuver, may be used. The interval 
between successive pilot actions must not be less than one second.
    2. The applicant must also demonstrate that the speed margin, 
established as above, will not be exceeded in inadvertent, or gust-
induced, upsets resulting in initiation of the dive from non-symmetric 
attitudes, unless the airplane is protected by the flight-control laws 
from getting into non-symmetric upset conditions. The upset maneuvers 
described in AC 25-7C, Chapter 2, Section 8, Paragraph 32c.(3)(a) and 
(c), may be used to comply with this requirement.
    3. Detected loss of the high-speed protection function must be less 
than 10-3 per flight hour.
    4. Failures of the system must be annunciated to the pilots. The 
Operating Limitations Section of the AFM must contain instructions that 
reduce the maximum operating speeds, Vmax/Mmax, 
to a value that maintains a speed margin between these speeds and

[[Page 49429]]

VD/MD that is consistent with showing compliance 
to Sec.  25.335(b), without the benefit of the high-speed protection 
system.
    5. Dispatch of the airplane with the high-speed protection system 
inoperative is prohibited except under an approved MEL that requires 
AFM instructions to indicate reduced maximum operating speeds, as 
described in special condition (4), above. In addition, the cockpit 
display of the reduced operating speeds, as well as the overspeed 
warning for exceeding those speeds, must be equivalent to that of the 
normal airplane with the high-speed protection system operative. Also, 
it must be shown that no additional hazards are introduced with the 
high-speed protection system inoperative.

    Issued in Renton, Washington, on July 30, 2014.
Jeffrey E. Duven,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2014-19824 Filed 8-20-14; 8:45 am]
BILLING CODE 4910-13-P