Proposed Rule2023-24312
Special Conditions: Airbus Model A321neo XLR Airplane; Electronic Flight-Control System: Lateral-Directional and Longitudinal Stability, and Low-Energy Awareness.
Primary source
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Published
November 3, 2023
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
This action proposes special conditions for the Airbus Model A321neo XLR airplane. The airplane will have a novel or unusual design feature when compared to the state of technology envisioned in the airworthiness standards for transport-category airplanes. This design feature is an electronic flight-control system (EFCS) associated with lateral-directional and longitudinal stability, and low-energy awareness. 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.
Full Text
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<title>Federal Register, Volume 88 Issue 212 (Friday, November 3, 2023)</title>
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[Federal Register Volume 88, Number 212 (Friday, November 3, 2023)]
[Proposed Rules]
[Pages 75517-75520]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2023-24312]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. FAA-2021-1034; Notice No. 25-23-02-SC]
Special Conditions: Airbus Model A321neo XLR Airplane; Electronic
Flight-Control System: Lateral-Directional and Longitudinal Stability,
and Low-Energy Awareness.
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed special conditions.
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SUMMARY: This action proposes special conditions for the Airbus Model
A321neo XLR airplane. The airplane will have a novel or unusual design
feature when compared to the state of technology envisioned in the
airworthiness standards for transport-category airplanes. This design
feature is an electronic flight-control system (EFCS) associated with
lateral-directional and longitudinal stability, and low-energy
awareness. 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: Send comments on or before December 4, 2023.
ADDRESSES: Send comments identified by Docket No. FAA-2021-1034 using
any of the following methods:
Federal eRegulations Portal: Go to <a href="https://www.regulations.gov/">https://www.regulations.gov/</a> 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.
Docket: Background documents or comments received may be read at
<a href="https://www.regulations.gov/">https://www.regulations.gov/</a> at any time. Follow the online
instructions for accessing the docket or go 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.
FOR FURTHER INFORMATION CONTACT: Troy Brown, Performance and
Environment Unit, AIR-621A, Technical Policy Branch, Policy and
Standards Division, Aircraft Certification Service, Federal Aviation
Administration, 1801 S Airport Rd., Wichita, KS 67209-2190; telephone
and fax 405-666-1050; email <a href="/cdn-cgi/l/email-protection#077375687e29662965756870694761666629606871"><span class="__cf_email__" data-cfemail="93e7e1fceabdf2bdf1e1fce4fdd3f5f2f2bdf4fce5">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION:
Comments Invited
The FAA invites 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 proposed special conditions,
explain the reason for any recommended change, and include supporting
data.
Certification of the Airbus Model A321neo XLR airplane is currently
scheduled for December 2023. The substance of these special conditions,
in all material respects, has been subject to the notice and public-
comment procedure in several prior instances. Therefore, because a
delay would significantly affect the applicant's installation of the
new or unusual feature, and delay certification of the airplane, the
FAA is reducing the public-comment period to 30 days.
The FAA will consider all comments received by the closing date for
comments, and will consider comments filed late if it is possible to do
so without incurring delay. The FAA may change these special conditions
based on the comments received.
Privacy
Except for Confidential Business Information (CBI) as described in
the following paragraph, and other information as described in title
14, Code of Federal Regulations (14 CFR) 11.35, the FAA will post all
comments received without change to <a href="https://www.regulations.gov/">https://www.regulations.gov/</a>,
including any personal information you provide. The FAA will also post
a report summarizing each substantive verbal contact received about
these special conditions.
Confidential Business Information
Confidential Business Information (CBI) is commercial or financial
information that is both customarily and actually treated as private by
its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552),
CBI is exempt from public disclosure. If your
[[Page 75518]]
comments responsive to these special conditions contain commercial or
financial information that is customarily treated as private, that you
actually treat as private, and that is relevant or responsive to these
special conditions, it is important that you clearly designate the
submitted comments as CBI. Please mark each page of your submission
containing CBI as ``PROPIN.'' The FAA will treat such marked
submissions as confidential under the FOIA, and the indicated comments
will not be placed in the public docket of these special conditions.
Send submissions containing CBI to the individual listed in the For
Further Information Contact section below. Comments the FAA receives,
which are not specifically designated as CBI, will be placed in the
public docket for these special conditions.
Background
On September 16, 2019, Airbus applied for an amendment to Type
Certificate No. A28NM to include the new Model A321neo XLR airplane.
These airplanes are twin-engine, transport-category airplanes with
seating for 244 passengers and a maximum takeoff weight of 222,000
pounds.
Static Lateral-Directional Stability
The EFCS on the Airbus Model A321neo XLR airplane contains fly-by-
wire control laws that can result in neutral static lateral-directional
stability. Therefore, the airplane does not meet the conventional
requirements in the regulations which require positive static lateral-
directional stability.
Positive static directional stability is defined as the tendency to
recover from a skid with the rudder free. Positive static lateral
stability is defined as the tendency to raise the low wing in a
sideslip with the aileron controls free. These control criteria are
intended to accomplish the following:
(a) Provide additional cues of inadvertent sideslips and skids
through control-force changes.
(b) Ensure that short periods of unattended operation do not result
in any significant changes in yaw or bank angle.
(c) Provide predictable roll and yaw response.
(d) Provide an acceptable level of pilot attention (workload) to
attain and maintain a coordinated turn.
Neutral static lateral-directional stability, conversely, means
that the airplane will stay in its new attitude when disturbed by an
external force (e.g., crosswind). Therefore, the regulations under 14
CFR 25.171 for the Airbus Model A321neo XLR airplane are inadequate.
Static Longitudinal Stability
Static longitudinal stability on airplanes with mechanical links to
the pitch-control surface means that a pull force on the controller
results in a reduction in speed relative to the trim speed, and a push
force results in higher than trim speed. Longitudinal stability is
required by the regulations for the following reasons:
(a) Speed-change cues are provided to the pilot through increased
and decreased forces on the controller.
(b) Short periods of unattended control of the airplane do not
result in significant changes in attitude, airspeed, or load factor.
(c) A predictable pitch response is provided to the pilot.
(d) An acceptable level of pilot attention (workload) to attain and
maintain trim speed and altitude is provided to the pilot.
(e) Longitudinal stability provides gust stability.
The pitch-control movement of the side stick on the Airbus Model
A321neo XLR airplane is designed to be a normal load factor, or ``g''
command, that results in an initial movement of the elevator surface to
attain the commanded load factor that is then followed by integrated
movement of the stabilizer and elevator to automatically trim the
airplane to a neutral, 1g, stick-free stability. The flight path
commanded by the initial side-stick input will remain stick-free until
the pilot provides another command. This control function is applied
during ``normal'' control law within the speed range, from initiation
of the angle-of-attack protection limit, V[alpha]<INF>prot</INF>, to
V<INF>MO</INF>/M<INF>MO</INF>. Once outside this speed range, the
control laws introduce the conventional longitudinal static stability
as described above.
As a result of neutral static stability, the Airbus Model A321neo
XLR airplane does not meet the regulatory requirements for static
longitudinal stability during normal operations.
Low Energy Awareness
Past experience on airplanes fitted with a flight-control system
providing neutral longitudinal stability reveals insufficient feedback
cues to the pilot of excursion below normal operational speeds. The
maximum angle-of-attack protection system limits the airplane angle of
attack and prevents stall during normal operating speeds, but this EFCS
is not sufficient to prevent stall at low-speed excursions below normal
operational speeds. Until intervention, there are no stability cues
because the aircraft remains trimmed. Additionally, feedback from the
pitching moment due to thrust variation is reduced by the flight-
control laws. Low-speed excursions may become more hazardous without
the typical longitudinal stability, and recovery is more difficult when
the low-speed situation is associated with a low altitude, and with the
engines at low thrust or with performance-limiting conditions.
Type Certification Basis
Under the provisions of 14 CFR 21.101, Airbus must show that the
Model A321neo XLR airplane meets the applicable provisions of the
regulations listed in Type Certificate No. A28NM, or the applicable
regulations in effect on the date of application for the change, except
for earlier amendments as agreed upon by the FAA.
If the Administrator finds that the applicable airworthiness
regulations (e.g., 14 CFR part 25) do not contain adequate or
appropriate safety standards for the Airbus Model A321neo XLR 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 novel or
unusual design feature, or should any other model already included on
the same type certificate be modified to incorporate the same novel or
unusual design feature, these special conditions would also apply to
the other model under Sec. 21.101.
In addition to the applicable airworthiness regulations and special
conditions, the Airbus Model A321neo XLR 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 issues special conditions, as defined in Sec. 11.19, in
accordance with Sec. 11.38, and they become part of the type
certification basis under Sec. 21.101.
Novel or Unusual Design Features
The Airbus Model A321neo XLR airplane will incorporate the
following novel or unusual design feature:
An electronic flight-control system (EFCS) associated with lateral-
directional and longitudinal stability, and low-energy awareness.
[[Page 75519]]
Discussion
In the absence of positive lateral stability, the curve of lateral
control-surface deflections against sideslip angle should be, in a
conventional sense and reasonably in harmony with, rudder deflection
during steady-heading sideslip maneuvers.
Because conventional relationships between stick forces and
control-surface displacements do not apply to the ``load-factor
command'' flight-control system on the Airbus Model A321neo XLR
airplane, longitudinal stability characteristics should be evaluated by
assessing the airplane's handling qualities during simulator and
flight-test maneuvers appropriate to operation of the airplane.
Additionally, there is recognition that under icing and non-icing
conditions, there may be a difference in full pedal deflection. This
difference may result in changes to testing before reaching full pedal
and the special conditions account for these differences.
The airplane must provide adequate awareness cues to the pilot of a
low-energy (low-speed/low-thrust/low-height) state to ensure that the
airplane retains sufficient energy to recover when flight-control laws
provide neutral longitudinal stability significantly below the normal
operating speeds. ``Adequate awareness'' means that information must be
provided to alert the crew of unsafe operating conditions and to enable
them to take appropriate corrective action. Testing of these awareness
cues should occur by simulator and flight test in the operational
flight envelope for which certification is requested. Testing should
include a sufficient number of tests to allow the level of energy
awareness, and the effects of energy-management errors, to be assessed.
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.
Applicability
As discussed above, these special conditions apply to Airbus Model
A321neo XLR airplane. 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 one model series of airplanes. It is not a rule of general
applicability.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
Authority Citation
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(f), 106(g), 40113, 44701, 44702, and
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 A321neo XLR airplane. These special conditions are
issued in lieu of the paragraphs of 14 CFR part 25 referenced below.
Static Lateral-Directional Stability
(a) In lieu of compliance with Sec. 25.171, the airplane must have
lateral and directional stability characteristics in accordance with
Sec. 25.177. In addition, both suitable stability and suitable control
feel are required in any condition normally encountered in service.
(b) In lieu of compliance with Sec. 25.177(c), the following
requirement must be met for the configurations and speed specified in
Sec. 25.177(a).
(1) In straight, steady sideslips over the range of sideslip angles
appropriate to the operation of the airplane, the directional control
movements and forces must be substantially proportional to the angle of
sideslip in a stable sense. The factor of proportionality must lie
between limits found necessary for safe operation. During these
straight, steady sideslips, necessary lateral control movements and
forces must not be in the unstable sense with the exception of speeds
above V<INF>mo</INF>/M<INF>mo</INF> per Sec. 25.177(b)(2). The range
of sideslip angles evaluated must include those sideslip angles
resulting from the lesser of:
(i) One-half of the available directional (pedal) control input;
and
(ii) A directional (pedal) control force of 180 pounds.
(c) In lieu of compliance with Sec. 25.177(d), the following
requirements must be met:
(2) In non-icing conditions, for sideslip angles greater than those
prescribed by Sec. 25.177(a), up to the angle at which full rudder
control is used or a rudder control force of 180 pounds is obtained,
the rudder control forces may not reverse, and increased rudder
deflection must be needed for increased angles of sideslip. Compliance
with this requirement must be shown using straight, steady sideslips,
unless full lateral control input is achieved before reaching either
full rudder control input or a rudder control force of 180 pounds; a
straight, steady sideslip need not be maintained after achieving full
lateral control input. This requirement must be met at all approved
landing gear and flap positions for the range of operating speeds and
power conditions appropriate to each landing gear and flap position
with all engines operating.
(3) In icing conditions, in the configurations listed below, trim
the airplane at the specified speed and conduct steady heading
sideslips over the range of sideslip angles appropriate to the
operation of the airplane but not less than those obtained with one-
half of available rudder control input.
(i) High lift devices retracted configuration: trim at best rate of
climb speed but not less than minimum all engines operating climb speed
defined for icing conditions.
(ii) Lowest lift take-off configuration: trim at the all engines
operating initial climb speed defined for icing conditions.
(iii) Landing configurations: trim at minimum landing speed defined
for icing conditions.
Longitudinal Stability
In lieu of compliance with the requirements of Sec. Sec. 25.171,
25.173, and 25.175, the airplane must be shown to have longitudinal
stability characteristics in accordance with the following conditions.
In addition, both suitable stability and suitable control feel are
required in any condition normally encountered in service, including
the effects of atmospheric disturbance.
(a) Strong positive static longitudinal stability (1 pound per 6
knots applied through the sidestick) must be present which provides
adequate awareness cues to the crew that the speed is above
V<INF>mo</INF>/M<INF>mo</INF> or below the minimum speed for hands-free
stabilized flight. Static longitudinal characteristics must be shown to
be suitable based on the airplane handling qualities, including an
evaluation of pilot workload and pilot compensation, for specific test
procedures during the flight-test evaluations. These characteristics
must be shown for appropriate combinations of airplane configuration
(i.e., flaps extended or retracted, gear deployed or stowed) and thrust
for climb, cruise, approach, landing and go-around.
(1) Release of the controller at speeds above V<INF>mo</INF>/
M<INF>mo</INF>, or below the minimum speed for hands-free stabilized
flight, must produce a prompt recovery towards normal operating speeds
[[Page 75520]]
without resulting in a hazardous condition.
(2) The design must not allow a pilot to re-trim the controller
forces resulting from this stability.
Low Energy Awareness
The airplane must provide adequate awareness cues to the pilot of a
low-energy (low-speed/low-thrust/low-height) state to ensure that the
airplane retains sufficient energy to recover when flight-control laws
provide neutral longitudinal stability significantly below the normal
operating speeds. This should be accomplished as follows:
(a) Adequate low speed/low thrust cues at low altitude should be
provided by a strong positive static stability force gradient (1 pound
per 6 knots applied through the sidestick), or
(b) The low energy awareness should be provided by an appropriate
warning with the following characteristics. The low-energy awareness
should:
(1) Be unique, unambiguous, and unmistakable.
(2) Be active at appropriate altitudes and in appropriate
configurations (i.e., at low altitude, in the approach and landing
configurations).
(3) Be sufficiently timely to allow recovery to a stabilized flight
condition inside the normal flight envelope while maintaining the
desired flight path and without entering the flight controls angle-of-
attack protection mode.
(4) Not be triggered during normal operation, including operation
in moderate turbulence for recommended maneuvers at recommended speeds.
(5) Not be cancelable by the pilot other than by achieving a higher
energy state.
(6) Have an adequate hierarchy among the various warnings so that
the pilot is not confused and led to take inappropriate recovery action
if multiple warnings occur.
Global energy awareness and non-nuisance on low-energy cues must be
evaluated by simulator and flight tests in the whole take-off and
landing altitude range for which certification is requested. This
includes all relevant combinations of weight, center-of-gravity
position, configuration, airbrakes position, and available thrust,
including reduced and derated take-off thrust operations and engine-
failure cases. The tests must assess the level of energy awareness, and
the effects of energy-management errors.
Issued in in Kansas City, Missouri, on October 27, 2023.
Patrick R. Mullen,
Manager, Technical Policy Branch, Policy and Standards Division,
Aircraft Certification Service.
[FR Doc. 2023-24312 Filed 11-2-23; 8:45 am]
BILLING CODE 4910-13-P
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