[Federal Register Volume 79, Number 5 (Wednesday, January 8, 2014)]
[Proposed Rules]
[Pages 1339-1341]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2014-00105]



Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2013-0911; Notice No. 25-13-22-SC]

Special Conditions: Airbus, Model A350-900 Series Airplane; 
Lateral Trim Function Through Differential Flap Setting

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed special conditions.


SUMMARY: This action proposes special conditions for the Airbus Model 
A350-900 series airplanes. These airplanes will have a novel or unusual 
design feature associated with a lateral trim function that deploys 
flaps asymmetrically for airplane lateral trim control. This function 
replaces the traditional method of providing airplane lateral trim over 
a small range through flap and aileron mechanical rigging. The 
applicable airworthiness regulations do not contain adequate or 
appropriate safety standards for this design feature. These proposed 
special conditions contain the additional safety standards that the 
Administrator considers necessary to establish a level of safety

[[Page 1340]]

equivalent to that established by the existing airworthiness standards.

DATES: Send your comments on or before February 24, 2014.

ADDRESSES: Send comments identified by docket number FAA-2013-0911 
using any of the following methods:
     Federal eRegulations Portal: Go to http://www.regulations.gov/ and follow the online instructions for sending 
your comments electronically.
     Mail: Send comments to Docket Operations, M-30, U.S. 
Department of Transportation (DOT), 1200 New Jersey Avenue SE., Room 
W12-140, West Building Ground Floor, Washington, DC 20590-0001.
     Hand Delivery or Courier: Take comments to Docket 
Operations in Room W12-140 of the West Building Ground Floor at 1200 
New Jersey Avenue SE., Washington, DC, between 9 a.m. and 5 p.m., 
Monday through Friday, except federal holidays.
     Fax: Fax comments to Docket Operations at 202-493-2251.
    Privacy: The FAA will post all comments it receives, without 
change, to http://www.regulations.gov/, including any personal 
information the commenter provides. Using the search function of the 
docket Web site, anyone can find and read the electronic form of all 
comments received into any FAA docket, including the name of the 
individual sending the comment (or signing the comment for an 
association, business, labor union, etc.). DOT's complete Privacy Act 
Statement can be found in the Federal Register published on April 11, 
2000 (65 FR 19477-19478), as well as at http://DocketsInfo.dot.gov/.
    Docket: Background documents or comments received may be read at 
http://www.regulations.gov/ at any time. Follow the online instructions 
for accessing the docket or go to the Docket Operations in Room W12-140 
of the West Building Ground Floor at 1200 New Jersey Avenue SE., 
Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, 
except federal holidays.

Mechanical Systems, ANM-112, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98057-
3356; telephone (425) 227-1234; facsimile (425) 227-1320.


Comments Invited

    We invite interested people to take part in this rulemaking by 
sending written comments, data, or views. The most helpful comments 
reference a specific portion of the special conditions, explain the 
reason for any recommended change, and include supporting data.
    We will consider all comments we receive on or before the closing 
date for comments. We may change these proposed special conditions 
based on the comments we receive.


    On August 25, 2008, Airbus applied for a type certificate for their 
new Model A350-900 series airplane. Later, Airbus requested and the FAA 
approved an extension to the application for FAA type certification to 
June 28, 2009. The Model A350-900 series 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 series configuration will accommodate 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. Airbus proposes the 
Model A350-900 series to be certified for extended operations (ETOPS) 
beyond 180 minutes at entry into service for up to a 420-minute maximum 
diversion time.
    On conventional airplanes, small lateral airplane asymmetries have 
typically been addressed through flap and aileron rigging (e.g., using 
shims). On Model A350-900 series airplanes, an order for asymmetric 
flap deployment will be computed by the primary flight control system 
as a function of the aileron position. The current airworthiness 
standards do not contain adequate safety standards for asymmetric use 
of the flaps as proposed for Airbus Model A350-900 series airplanes. 
Special conditions are needed to account for the aspects of a function 
used to command an intended flap asymmetry. The lateral trim function 
is intended to be performed once during climb and once during cruise to 
compensate for small airplane lateral asymmetries.
    The lateral trim function is not a trim control system in the 
conventional sense as it has no pilot interface and is not governed by 
Sec.  25.677. In fact some fly-by-wire airplanes have no pilot operated 
lateral trim at all. The lateral trim function is simply an additional 
fly-by-wire flight control function that nulls small roll asymmetries 
in certain flight phases with small asymmetric flap deployments. 
Although the function operates under normal conditions within the small 
range of the traditional rigging, there may be failure cases leading to 
a significant out of range asymmetric flap condition. An asymmetry 
threshold will protect the system against excessive flap asymmetry.

Type Certification Basis

    Under Title 14, Code of Federal Regulations (14 CFR) 21.17, Airbus 
must show that the Model A350-900 series meets the applicable 
provisions of 14 CFR part 25, as amended by Amendments 25-1 through 25-
    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 series 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 novel or 
unusual design feature, the proposed special conditions would also 
apply to the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and 
proposed special conditions, the Model A350-900 series 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 and the FAA must 
issue a finding of regulatory adequacy under Sec.  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 series will incorporate the following 
novel or unusual design features: the asymmetric use of flaps to 
address lateral trim which is not adequately addressed by Sec.  25.701.


    Title 14 Code of Federal Regulations (14 CFR) part 25 Sec.  
25.701(a) requires that unless the airplane has safe flight 
characteristics with the flaps or slats retracted on one side and 
extended on the other, flap and slat surfaces must be synchronized by 
either a mechanical interconnection or any equivalent means that has 
the same integrity. Synchronization is interpreted to mean that flap 
movement is symmetrical throughout the full range of flap motion. 
Because the lateral trim function

[[Page 1341]]

intentionally creates asymmetric flap motions, the flap system 
installation of the Model A350-900 series does not meet the requirement 
of Sec.  25.701(a) and (d).


    As discussed above, these proposed special conditions apply to 
Airbus Model A350-900 series 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 proposed 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 series airplanes. It is not a rule of 
general applicability.

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 Proposed Special Conditions

    Accordingly, the Federal Aviation Administration (FAA) proposes the 
following special conditions as part of the type certification basis 
for Airbus Model A350-900 series airplanes.
    1. Lateral Trim Function through Differential Flap Setting.
    Current airworthiness standards, specifically Sec.  25.701, do not 
contain adequate safety standards for the proposed design. In lieu of 
the requirements of Sec.  25.701(a) and (d) for the lateral trim 
function, the following special condition is proposed:
    a. Airbus must demonstrate that an unsafe condition is not created 
by using the flaps asymmetrically,
    b. The degree of acceptable asymmetry must be defined and justified 
for all flight phases with respect to:
     Sec.  25.701(b) and (c), with the worst case asymmetric 
flap configurations, and
     providing equivalent protection against excess asymmetry 
in the same manner as Sec.  25.701 provides to systems that are 
synchronized or use another equivalent means to prevent asymmetry.
    c. This lateral trim function is a flight control system and 
therefore must show compliance to both general system requirements as 
well as general flight control requirements. Therefore, the function 
must be demonstrated not to embody, where practicable, significant 
latent failures.

    Issued in Renton, Washington, on October 22, 2013.
Stephen P. Boyd,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
[FR Doc. 2014-00105 Filed 1-7-14; 8:45 am]