Special Conditions: Bell Textron Inc. Model 525 Helicopter; Fly-By-Wire Flight Control System, 2689-2692 [2022-00862]
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Federal Register / Vol. 87, No. 12 / Wednesday, January 19, 2022 / Rules and Regulations
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PART 430—ENERGY CONSERVATION
PROGRAM FOR CONSUMER
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1. The authority citation for part 430
continues as follows:
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2461 note.
2. Section 430.32 is amended by:
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■
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*
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(g) * * *
(4) Clothes washers manufactured on
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Integrated modified
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Product class
(i) Top-loading, Compact (less than 1.6 ft 3 capacity) .............................................................
(ii) Top-loading, Standard (1.6 ft 3 or greater capacity) ...........................................................
(iii) Front-loading, Compact (less than 1.6 ft 3 capacity) .........................................................
(iv) Front-loading, Standard (1.6 ft 3 or greater capacity) .......................................................
(h) * * *
Integrated water factor
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(3) Clothes dryers manufactured on or
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(iv) Vented Gas ....................................................................................................................................................................
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BILLING CODE 6450–01–P
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 29
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[Docket No. FAA–2021–0065; Special
Conditions No. 29–054–SC]
Special Conditions: Bell Textron Inc.
Model 525 Helicopter; Fly-By-Wire
Flight Control System
Federal Aviation
Administration (FAA), DOT.
ACTION: Final special conditions.
AGENCY:
16:00 Jan 18, 2022
These special conditions are
issued for the Bell Textron Inc. (Bell)
Model 525 helicopter. This helicopter
will have a novel or unusual design
feature associated with a fly-by-wire
(FBW) flight control system (FCS). 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 February 18, 2022.
FOR FURTHER INFORMATION CONTACT: John
VanHoudt, FAA, Dynamic Systems
Section, AIR–627, Technical Innovation
Policy Branch, Policy and Innovation
SUMMARY:
[FR Doc. 2022–00833 Filed 1–18–22; 8:45 am]
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Division, Aircraft Certification Service,
10101 Hillwood Parkway, Fort Worth,
TX 76177–1524; telephone and fax 817–
222–5193; email John.G.Van.Houdt@
FAA.Gov.
SUPPLEMENTARY INFORMATION:
Background
On December 15, 2011, Bell applied
for a type certificate for a new transport
category helicopter, designated as the
Model 525, under Title 14, Code of
Federal Regulations (CFR) part 29. Bell
applied for multiple extensions, with
the most recent occurring on November
12, 2020. The date of the updated type
certification basis is December 31, 2016,
based upon the applicant’s proposed
type certificate issuance date of
December 31, 2021. The Model 525 is a
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Federal Register / Vol. 87, No. 12 / Wednesday, January 19, 2022 / Rules and Regulations
medium twin-engine rotorcraft. The
design maximum takeoff weight is
20,500 pounds, with a maximum
capacity of 19 passengers and a crew of
two.
The Bell Model 525 helicopter will be
equipped with a four axis full authority
digital FBW FCS that provides for
aircraft control through pilot input and
coupled flight director modes. The
design of the Bell Model 525 FBW
controls, which provides no direct
hydro-mechanical linkage between the
primary cockpit flight controls or
inceptors and the main and tail rotor
actuators, is a first for commercial
rotorcraft use. Therefore, the regulations
do not contain adequate or appropriate
safety standards for this new design
feature.
The rotorcraft industry is producing
new generations of helicopters, and
gradually increasing size, speed, load
capacity, and technical sophistication.
In recent years, an accelerated trend has
occurred using rotorcraft for a wide
range of commercial and industrial
applications. This has resulted in
increased complexity of modern control
systems and increased use of
automation in flight control systems,
including the implementation of
advanced flight control systems such as
FBW FCS.
Section 29.671(c), which provides
requirements for transport category
rotorcraft control systems, does not
contain adequate or appropriate safety
standards for this new design feature.
Section 29.671(c) requires, in part, a
means to allow the pilot to determine
that full control authority is available
prior to flight. This command control
authority is typically achieved by
verifying movement of the control
quadrant through an unassisted
mechanical pilot-initiated manipulation
of the primary flight controls prior to
flight. Although this approach does not
guarantee that 100% maximum control
movement of the flight controls has
been achieved prior to flight, it has been
deemed appropriate for mechanical
flight control systems.
Unlike traditional mechanical flight
control systems, the FBW FCS reduces
the opportunity for jamming of the flight
controls due to mechanical bind,
improper servo adjustment resulting
from faulty maintenance, or presence of
a foreign object in the control
mechanism that will impair safety. This
reduced exposure for jams is due to the
replacement of the mechanical linkages
between the primary cockpit flight
controls or inceptors and the main and
tail rotor actuators with digital signal
processing wiring. However, the FBW
FCS does increase the potential for
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latent failures or faults that could impair
full control authority, unless a means
exists to ensure the FBW FCS is fully
functional and free of control authority
impairment prior to flight. A FBW
system may have the ability to verify
full control authority without having to
move the primary flight controls.
Although part 29 does not contain
adequate or appropriate safety standards
for this novel or unusual design feature,
14 CFR 25.671, amendment 25–23,
provides these requirements for
transport category airplanes.
Accordingly, these special conditions
are based on § 25.671 to provide
requirements for a FBW FCS on the Bell
Model 525 helicopter. Section 25.671(c)
provides the same level of safety as
intended by § 29.671(c) when
employing a FBW FCS by including
requirements for jamming and failure
analysis. These special conditions
require a comprehensive safety analysis
of the aircraft’s FBW FCS to include
failures due to command logic
(software), mechanical and electronic
interfaces to other systems, jamming,
and maintenance. Therefore, in
conjunction with § 29.671(a) and (b),
these special conditions incorporate
provisions from § 25.671(c) to establish
a level of safety equivalent to that
established in the regulations.
Type Certification Basis
Under the provisions of 14 CFR 21.17,
Bell must show that the Model 525
helicopter meets the applicable
provisions of part 29, as amended by
Amendments 29 through 55 thereto. The
Bell Model 525 certification basis date
is December 31, 2016.
If the Administrator finds that the
applicable airworthiness regulations
(i.e., part 29) do not contain adequate or
appropriate safety standards for the Bell
Model 525 because of a novel or
unusual design feature, special
conditions are prescribed under the
provisions of § 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 § 21.101.
In addition to the applicable
airworthiness regulations and special
conditions, the Bell Model 525
helicopter must comply with the noise
certification requirements of 14 CFR
part 36, and the FAA must issue a
finding of regulatory adequacy under
§ 611 of Public Law 92–574, the ‘‘Noise
Control Act of 1972.’’
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The FAA issues special conditions, as
defined in 14 CFR 11.19, in accordance
with § 11.38, and they become part of
the type-certification basis under
§ 21.17(a)(2).
Novel or Unusual Design Features
The Bell Model 525 helicopter will
incorporate the following novel or
unusual design features: A FBW FCS.
This new design feature has no direct
hydro-mechanical linkage between the
primary cockpit flight controls or
inceptors and the main and tail rotor
actuators, thereby eliminating the more
complex elements of either a manual
movement of the controls by the pilot,
or another manual means.
Discussion
These special conditions require that
a means be available to show full
control authority for all powered control
systems.
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
The FAA issued Notice of Proposed
Special Conditions No. 29–054–SC for
the Bell Model 525 helicopter, which
published in the Federal Register on
January 29, 2021 (86 FR 7516). The FAA
received one response, from the
European Union Aviation Safety Agency
(EASA).
The FAA proposed the special
conditions, which are based on current
§ 25.671(c), in lieu of § 29.671(c). EASA
requested the FAA explain its rationale
for replacing § 29.671(c), which requires
a means to allow either full movement
of all primary flight controls or a
determination by the pilot that full
control authority is available prior to
flight. EASA stated that although FBW
reduces the risk of jamming, it does not
alleviate the need to allow checking the
full control movement prior to flight
and thus a pre-flight check is still
necessary.
The FAA is not replacing the
requirement for a pre-flight check.
Instead, these special conditions
include a requirement for a
comprehensive safety analysis to ensure
the FBW FCS is fully functional and free
of control authority impairment prior to
flight. The comprehensive safety
analysis should address failures due to
command logic (software), mechanical
and electronic interfaces to other
systems, jamming, and maintenance.
The safety analysis should also identify
the existence of any latent faults.
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Federal Register / Vol. 87, No. 12 / Wednesday, January 19, 2022 / Rules and Regulations
Therefore, the means to ensure the FBW
FCS is fully functional and free of
control authority impairment prior to
flight is based on the results of the
comprehensive safety analysis. The
means to ensure the safety objective of
the special conditions is met may
consist of design, analysis, test, built in
test, and limited pre-flight checks.
EASA noted the proposed special
conditions, although derived from
§ 25.671(c), are not aligned with EASA’s
latest Certification Specifications (CS)
25.671 (Amendment 24).
Under § 21.16, special conditions
prescribed by the FAA must establish a
level of safety equivalent to that
established in the FAA’s existing
regulations. Accordingly, the FAA based
these special conditions on 14 CFR
25.671(c) and not on EASA’s
certification specifications.
EASA requested the FAA clarify its
use of the term ‘‘continued safe flight
and landing’’ used in the proposed
special conditions. EASA stated the
term has a specific definition for flight
control failures on large airplanes and
asked whether the FAA will use a
consistent definition for failure
conditions under § 29.1309. EASA also
asked whether the FAA will provide a
definition of ‘‘continued safe flight and
landing’’ in the context of flight control
failures.
Advisory Circular 29–2C, Certification
of Transport Category Rotorcraft (AC
29–2C), contains a definition for
‘‘continued safe flight and landing.’’ The
FAA plans to use this definition for the
purposes of these special conditions.
EASA stated the proposed special
conditions introduce the term ‘‘normal
flight envelope,’’ which is not present in
EASA’s CS 29 regulation. EASA
questioned whether it is relevant only to
the Bell Model 525 and whether it
means the same as ‘‘operating’’
envelope.
When § 25.671 was incorporated, the
‘‘normal flight envelope’’ was the
aircraft approved operating limitations
contained in the aircraft flight manual.
This proposed special condition has the
same intent. In order to provide clarity
and consistency in the language
between this special condition and
§ 29.672, the wording will be revised to
approved operating limitations.
EASA asked what the FAA means by
the proposed requirement that
‘‘probable failures have only minor
effects.’’ Specifically, EASA asked
whether a probable failure is greater
than 1E¥5 per flight hour and whether
‘‘no safety effect’’ would be a
noncompliance.
In AC 29–2C, the upper part of the
range previously applied to the term
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‘‘probable’’ has been redefined as
‘‘reasonably probable.’’ Accordingly, the
FAA has revised these special
conditions by replacing ‘‘probable’’ with
‘‘reasonably probable.’’ As provided in
AC 29–2C, reasonably probable events
are based on a probability on the order
of between 10¥3 to 10¥5. If a failure is
classified as ‘‘no safety effect,’’ then no
further showing of compliance would be
required.
EASA requested the FAA change the
language in paragraphs (1) and (2) of the
proposed special conditions to reference
failures as defined in § 29.671(c)(3).
EASA states its suggested language will
avoid a gap between EASA CS
29.671(c)(1) and 29.671(c)(3).
The FAA agrees and made the
suggested change in the special
conditions.
EASA stated that if the FAA’s special
conditions have a no single failure
criterion under § 29.1309, then jams
under § 29.671(c)(3) may need to be
excluded. EASA referenced CS 25.1309
(Amendment 24) for no single failure.
EASA is correct; there is no criteria
for single failure in § 29.1309. As such,
the FAA has removed the ‘‘single’’
descriptor from the special conditions
language to be consistent with § 29.1309
safety objectives. The FAA does not
agree that jams under § 29.671(c)(3)
need to be excluded. Any failure
condition that can be shown to be
extremely improbable isn’t limited by
failures that occur from a single source.
EASA stated that using language from
§ 25.671(c), which is applicable to
transport category airplanes, is overly
ambitious for rotorcraft. EASA asked
several hypothetical questions
concerning how an applicant would
show compliance and requested the
FAA provide further guidance.
Section 29.671(c), which these special
conditions replace as a certification
requirement for the Model 525, requires
either a means to allow full control
movement of the primary flight controls
prior to flight or a means that will allow
the pilot to determine that full control
authority is available prior to flight. The
language utilized from § 25.671(c) for
these special conditions ensures
verification of the control authority
prior to flight via a comprehensive
safety analysis. This analysis is
necessary to address failures that could
not be detected by full control
movement of the digital primary flight
controls.
EASA requested the FAA clarify
whether § 29.691 is sufficient for an
FBW system or whether specific
guidance is needed for FBW flight
controls after a power failure at entry
into and during autorotation.
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The requirements in § 29.691, and the
accompanying guidance in AC 29–2C,
are sufficient for an FBW system.
Section 29.691 requires that the flight
control design allow rapid entry into
autorotation after a power failure. AC
29–2C provides that applicants may
comply with this rule through an
evaluation as part of the Type
Inspection Authorization test program.
EASA requested the FAA clarify the
meaning of ‘‘normally encountered’’ in
paragraph (3) of the proposed special
conditions. Specifically, EASA asked
whether there are jams that are not
considered normal and are therefore
excluded from the assessment. EASA
further noted that the flight conditions
listed in paragraph (3) of the proposed
special conditions are contrary to the
maneuvers required by §§ 29.141 and
29.143.
The FAA intended these special
conditions to address jams encountered
during any flight condition including
transitions between flight conditions.
The FAA has revised paragraph (3)
accordingly.
EASA requested the FAA clarify the
relationship between the proposed
special conditions and § 29.685(a),
which addresses flight control jamming.
EASA noted the approach in § 29.685(a)
is different from the one proposed in the
special conditions, as § 29.685(a)
requires the design of the control system
to prevent jamming. EASA states the
proposed special conditions would not
provide credit for jamming that may
result in a condition where continued
safe flight is guaranteed.
Section 29.685(a) contains a design
requirement for mechanical controls
and is limited in scope. These special
conditions are broader and include FBW
primary flight controls that did not exist
when § 29.685 was promulgated in
1964. Regarding EASA’s statement
about credit, paragraph (3) of these
special conditions require reducing
jamming in any phase of flight to a level
capable of continued safe flight and
landing.
Applicability
These special conditions are
applicable to the Bell Model 525
helicopter. Should Bell apply at a later
date for a change to the type certificate
to include another model incorporating
the same novel or unusual design
feature, these special conditions would
apply to that model as well.
Conclusion
This action affects only a certain
novel or unusual design feature on the
Bell Model 525 helicopter. It is not a
rule of general applicability.
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List of Subjects in 14 CFR Part 29
ACTION:
Final rule; request for
comments.
Aircraft, Aviation safety, Reporting,
and recordkeeping requirements.
SUMMARY:
Authority Citation
The authority citation for these
special conditions is as follows:
Authority: 49 U.S.C. 106(f), 106(g), 40113,
44701–44702, 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 the Bell Textron
Inc. Model 525 helicopter. Unless
otherwise stated, the following special
conditions will be used in lieu of
§ 29.671(c).
The rotorcraft must be shown by
analysis and tests, to be capable of
continued safe flight and landing after
any of the following failures or jamming
in the flight control system for any
speed or altitude within the approved
operating limitations, without requiring
exceptional piloting skill or strength.
Reasonably probable failures must have
only minor effects.
(1) Any failure, excluding a jam as
listed in paragraph (3).
(2) Any combination of failures not
shown to be extremely improbable,
excluding a jam as listed in paragraph
(3).
(3) Any jam in a control position
encountered during any flight
condition, including transitions, within
the approved operating limitations,
unless the jam is shown to be extremely
improbable, or can be alleviated.
Issued in Kansas City, Missouri, on January
12, 2022.
Patrick Mullen,
Manager, Technical Innovation Policy
Branch, Policy and Innovation Division,
Aircraft Certification Service.
[FR Doc. 2022–00862 Filed 1–18–22; 8:45 am]
BILLING CODE 4910–13–P
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
jspears on DSK121TN23PROD with RULES1
[Docket No. FAA–2022–0004; Project
Identifier AD–2022–00036–T; Amendment
39–21913; AD 2022–02–16]
RIN 2120–AA64
Airworthiness Directives; The Boeing
Company Airplanes
Federal Aviation
Administration (FAA), DOT.
AGENCY:
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The FAA is adopting a new
airworthiness directive (AD) for all The
Boeing Company Model 787–8, 787–9,
and 787–10 airplanes. This AD was
prompted by a determination that radio
altimeters cannot be relied upon to
perform their intended function if they
experience interference from wireless
broadband operations in the 3.7–3.98
GHz frequency band (5G C-Band), and a
recent determination that, during
landings, as a result of this interference,
certain airplane systems may not
properly transition from AIR to
GROUND mode when landing on
certain runways, resulting in degraded
deceleration performance and longer
landing distance than normal due to the
effect on thrust reverser deployment,
speedbrake deployment, and increased
idle thrust. This AD requires revising
the limitations and operating
procedures sections of the existing
airplane flight manual (AFM) to
incorporate limitations prohibiting
certain landings and the use of certain
minimum equipment list (MEL) items,
and to incorporate operating procedures
for calculating landing distances, when
in the presence of 5G C-Band
interference as identified by Notices to
Air Missions (NOTAMs). The FAA is
issuing this AD to address the unsafe
condition on these products.
DATES: This AD is effective January 19,
2022.
The FAA must receive comments on
this AD by March 7, 2022.
ADDRESSES: You may send comments,
using the procedures found in 14 CFR
11.43 and 11.45, by any of the following
methods:
• Federal eRulemaking Portal: Go to
https://www.regulations.gov. Follow the
instructions for submitting comments.
• Fax: 202–493–2251.
• Mail: U.S. Department of
Transportation, Docket Operations, M–
30, West Building Ground Floor, Room
W12–140, 1200 New Jersey Avenue SE,
Washington, DC 20590.
• Hand Delivery: Deliver to Mail
address above between 9 a.m. and 5
p.m., Monday through Friday, except
Federal holidays.
Examining the AD Docket
You may examine the AD docket at
https://www.regulations.gov by
searching for and locating Docket No.
FAA–2022–0004; or in person at Docket
Operations between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal
holidays. The AD docket contains this
final rule, any comments received, and
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other information. The street address for
the Docket Operations is listed above.
FOR FURTHER INFORMATION CONTACT:
Dean Thompson, Senior Aerospace
Engineer, Systems and Equipment
Section, FAA, Seattle ACO Branch, 2200
South 216th St., Des Moines, WA 98198;
phone and fax: 206–231–3165; email:
dean.r.thompson@faa.gov.
SUPPLEMENTARY INFORMATION:
Background
In March 2020, the United States
Federal Communications Commission
(FCC) adopted final rules authorizing
flexible use of the 3.7–3.98 GHz band
for next generation services, including
5G and other advanced spectrum-based
services.1 Pursuant to these rules, CBand wireless broadband deployment is
permitted to occur in phases with the
opportunity for operations in the lower
0.1 GHz of the band (3.7–3.8 GHz) in
certain markets as early as January 19,
2022. This AD refers to ‘‘5G C-Band’’
interference, but wireless broadband
technologies, other than 5G, may use the
same frequency band.2 These other uses
of the same frequency band are within
the scope of this AD since they would
introduce the same risk of radio
altimeter interference as 5G C-Band.
The radio altimeter is an important
aircraft instrument, and its intended
function is to provide direct heightabove-terrain/water information to a
variety of aircraft systems. Commercial
aviation radio altimeters operate in the
4.2–4.4 GHz band, which is separated
by 0.22 GHz from the C-Band
telecommunication systems in the 3.7–
3.98 GHz band. The radio altimeter is
more precise than a barometric altimeter
and for that reason is used where
aircraft height over the ground needs to
be precisely measured, such as
autoland, manual landings, or other low
altitude operations. The receiver on the
radio altimeter is typically highly
accurate, however it may deliver
erroneous results in the presence of outof-band radio frequency emissions from
other frequency bands. The radio
altimeter must detect faint signals
reflected off the ground to measure
altitude, in a manner similar to radar.
Out-of-band signals could significantly
degrade radio altimeter functions during
critical phases of flight, if the altimeter
is unable to sufficiently reject those
signals.
1 The FCC’s rules did not make C-Band wireless
broadband available in Alaska, Hawaii, and the U.S.
Territories.
2 The regulatory text of the AD uses the term ‘‘5G
C-Band’’ which, for purposes of this AD, has the
same meaning as ‘‘5G’’, ‘‘C-Band’’ and ‘‘3.7–3.98
GHz.’’
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]]>Agencies
[Federal Register Volume 87, Number 12 (Wednesday, January 19, 2022)]
[Rules and Regulations]
[Pages 2689-2692]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-00862]
=======================================================================
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 29
[Docket No. FAA-2021-0065; Special Conditions No. 29-054-SC]
Special Conditions: Bell Textron Inc. Model 525 Helicopter; Fly-
By-Wire Flight Control System
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
-----------------------------------------------------------------------
SUMMARY: These special conditions are issued for the Bell Textron Inc.
(Bell) Model 525 helicopter. This helicopter will have a novel or
unusual design feature associated with a fly-by-wire (FBW) flight
control system (FCS). 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 February 18, 2022.
FOR FURTHER INFORMATION CONTACT: John VanHoudt, FAA, Dynamic Systems
Section, AIR-627, Technical Innovation Policy Branch, Policy and
Innovation Division, Aircraft Certification Service, 10101 Hillwood
Parkway, Fort Worth, TX 76177-1524; telephone and fax 817-222-5193;
email [email protected].
SUPPLEMENTARY INFORMATION:
Background
On December 15, 2011, Bell applied for a type certificate for a new
transport category helicopter, designated as the Model 525, under Title
14, Code of Federal Regulations (CFR) part 29. Bell applied for
multiple extensions, with the most recent occurring on November 12,
2020. The date of the updated type certification basis is December 31,
2016, based upon the applicant's proposed type certificate issuance
date of December 31, 2021. The Model 525 is a
[[Page 2690]]
medium twin-engine rotorcraft. The design maximum takeoff weight is
20,500 pounds, with a maximum capacity of 19 passengers and a crew of
two.
The Bell Model 525 helicopter will be equipped with a four axis
full authority digital FBW FCS that provides for aircraft control
through pilot input and coupled flight director modes. The design of
the Bell Model 525 FBW controls, which provides no direct hydro-
mechanical linkage between the primary cockpit flight controls or
inceptors and the main and tail rotor actuators, is a first for
commercial rotorcraft use. Therefore, the regulations do not contain
adequate or appropriate safety standards for this new design feature.
The rotorcraft industry is producing new generations of
helicopters, and gradually increasing size, speed, load capacity, and
technical sophistication. In recent years, an accelerated trend has
occurred using rotorcraft for a wide range of commercial and industrial
applications. This has resulted in increased complexity of modern
control systems and increased use of automation in flight control
systems, including the implementation of advanced flight control
systems such as FBW FCS.
Section 29.671(c), which provides requirements for transport
category rotorcraft control systems, does not contain adequate or
appropriate safety standards for this new design feature. Section
29.671(c) requires, in part, a means to allow the pilot to determine
that full control authority is available prior to flight. This command
control authority is typically achieved by verifying movement of the
control quadrant through an unassisted mechanical pilot-initiated
manipulation of the primary flight controls prior to flight. Although
this approach does not guarantee that 100% maximum control movement of
the flight controls has been achieved prior to flight, it has been
deemed appropriate for mechanical flight control systems.
Unlike traditional mechanical flight control systems, the FBW FCS
reduces the opportunity for jamming of the flight controls due to
mechanical bind, improper servo adjustment resulting from faulty
maintenance, or presence of a foreign object in the control mechanism
that will impair safety. This reduced exposure for jams is due to the
replacement of the mechanical linkages between the primary cockpit
flight controls or inceptors and the main and tail rotor actuators with
digital signal processing wiring. However, the FBW FCS does increase
the potential for latent failures or faults that could impair full
control authority, unless a means exists to ensure the FBW FCS is fully
functional and free of control authority impairment prior to flight. A
FBW system may have the ability to verify full control authority
without having to move the primary flight controls.
Although part 29 does not contain adequate or appropriate safety
standards for this novel or unusual design feature, 14 CFR 25.671,
amendment 25-23, provides these requirements for transport category
airplanes. Accordingly, these special conditions are based on Sec.
25.671 to provide requirements for a FBW FCS on the Bell Model 525
helicopter. Section 25.671(c) provides the same level of safety as
intended by Sec. 29.671(c) when employing a FBW FCS by including
requirements for jamming and failure analysis. These special conditions
require a comprehensive safety analysis of the aircraft's FBW FCS to
include failures due to command logic (software), mechanical and
electronic interfaces to other systems, jamming, and maintenance.
Therefore, in conjunction with Sec. 29.671(a) and (b), these special
conditions incorporate provisions from Sec. 25.671(c) to establish a
level of safety equivalent to that established in the regulations.
Type Certification Basis
Under the provisions of 14 CFR 21.17, Bell must show that the Model
525 helicopter meets the applicable provisions of part 29, as amended
by Amendments 29 through 55 thereto. The Bell Model 525 certification
basis date is December 31, 2016.
If the Administrator finds that the applicable airworthiness
regulations (i.e., part 29) do not contain adequate or appropriate
safety standards for the Bell Model 525 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 Bell Model 525 helicopter must comply with 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, in
accordance with Sec. 11.38, and they become part of the type-
certification basis under Sec. 21.17(a)(2).
Novel or Unusual Design Features
The Bell Model 525 helicopter will incorporate the following novel
or unusual design features: A FBW FCS.
This new design feature has no direct hydro-mechanical linkage
between the primary cockpit flight controls or inceptors and the main
and tail rotor actuators, thereby eliminating the more complex elements
of either a manual movement of the controls by the pilot, or another
manual means.
Discussion
These special conditions require that a means be available to show
full control authority for all powered control systems.
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
The FAA issued Notice of Proposed Special Conditions No. 29-054-SC
for the Bell Model 525 helicopter, which published in the Federal
Register on January 29, 2021 (86 FR 7516). The FAA received one
response, from the European Union Aviation Safety Agency (EASA).
The FAA proposed the special conditions, which are based on current
Sec. 25.671(c), in lieu of Sec. 29.671(c). EASA requested the FAA
explain its rationale for replacing Sec. 29.671(c), which requires a
means to allow either full movement of all primary flight controls or a
determination by the pilot that full control authority is available
prior to flight. EASA stated that although FBW reduces the risk of
jamming, it does not alleviate the need to allow checking the full
control movement prior to flight and thus a pre-flight check is still
necessary.
The FAA is not replacing the requirement for a pre-flight check.
Instead, these special conditions include a requirement for a
comprehensive safety analysis to ensure the FBW FCS is fully functional
and free of control authority impairment prior to flight. The
comprehensive safety analysis should address failures due to command
logic (software), mechanical and electronic interfaces to other
systems, jamming, and maintenance. The safety analysis should also
identify the existence of any latent faults.
[[Page 2691]]
Therefore, the means to ensure the FBW FCS is fully functional and free
of control authority impairment prior to flight is based on the results
of the comprehensive safety analysis. The means to ensure the safety
objective of the special conditions is met may consist of design,
analysis, test, built in test, and limited pre-flight checks.
EASA noted the proposed special conditions, although derived from
Sec. 25.671(c), are not aligned with EASA's latest Certification
Specifications (CS) 25.671 (Amendment 24).
Under Sec. 21.16, special conditions prescribed by the FAA must
establish a level of safety equivalent to that established in the FAA's
existing regulations. Accordingly, the FAA based these special
conditions on 14 CFR 25.671(c) and not on EASA's certification
specifications.
EASA requested the FAA clarify its use of the term ``continued safe
flight and landing'' used in the proposed special conditions. EASA
stated the term has a specific definition for flight control failures
on large airplanes and asked whether the FAA will use a consistent
definition for failure conditions under Sec. 29.1309. EASA also asked
whether the FAA will provide a definition of ``continued safe flight
and landing'' in the context of flight control failures.
Advisory Circular 29-2C, Certification of Transport Category
Rotorcraft (AC 29-2C), contains a definition for ``continued safe
flight and landing.'' The FAA plans to use this definition for the
purposes of these special conditions.
EASA stated the proposed special conditions introduce the term
``normal flight envelope,'' which is not present in EASA's CS 29
regulation. EASA questioned whether it is relevant only to the Bell
Model 525 and whether it means the same as ``operating'' envelope.
When Sec. 25.671 was incorporated, the ``normal flight envelope''
was the aircraft approved operating limitations contained in the
aircraft flight manual. This proposed special condition has the same
intent. In order to provide clarity and consistency in the language
between this special condition and Sec. 29.672, the wording will be
revised to approved operating limitations.
EASA asked what the FAA means by the proposed requirement that
``probable failures have only minor effects.'' Specifically, EASA asked
whether a probable failure is greater than 1E-5 per flight
hour and whether ``no safety effect'' would be a noncompliance.
In AC 29-2C, the upper part of the range previously applied to the
term ``probable'' has been redefined as ``reasonably probable.''
Accordingly, the FAA has revised these special conditions by replacing
``probable'' with ``reasonably probable.'' As provided in AC 29-2C,
reasonably probable events are based on a probability on the order of
between 10-3 to 10-5. If a failure is classified
as ``no safety effect,'' then no further showing of compliance would be
required.
EASA requested the FAA change the language in paragraphs (1) and
(2) of the proposed special conditions to reference failures as defined
in Sec. 29.671(c)(3). EASA states its suggested language will avoid a
gap between EASA CS 29.671(c)(1) and 29.671(c)(3).
The FAA agrees and made the suggested change in the special
conditions.
EASA stated that if the FAA's special conditions have a no single
failure criterion under Sec. 29.1309, then jams under Sec.
29.671(c)(3) may need to be excluded. EASA referenced CS 25.1309
(Amendment 24) for no single failure.
EASA is correct; there is no criteria for single failure in Sec.
29.1309. As such, the FAA has removed the ``single'' descriptor from
the special conditions language to be consistent with Sec. 29.1309
safety objectives. The FAA does not agree that jams under Sec.
29.671(c)(3) need to be excluded. Any failure condition that can be
shown to be extremely improbable isn't limited by failures that occur
from a single source.
EASA stated that using language from Sec. 25.671(c), which is
applicable to transport category airplanes, is overly ambitious for
rotorcraft. EASA asked several hypothetical questions concerning how an
applicant would show compliance and requested the FAA provide further
guidance.
Section 29.671(c), which these special conditions replace as a
certification requirement for the Model 525, requires either a means to
allow full control movement of the primary flight controls prior to
flight or a means that will allow the pilot to determine that full
control authority is available prior to flight. The language utilized
from Sec. 25.671(c) for these special conditions ensures verification
of the control authority prior to flight via a comprehensive safety
analysis. This analysis is necessary to address failures that could not
be detected by full control movement of the digital primary flight
controls.
EASA requested the FAA clarify whether Sec. 29.691 is sufficient
for an FBW system or whether specific guidance is needed for FBW flight
controls after a power failure at entry into and during autorotation.
The requirements in Sec. 29.691, and the accompanying guidance in
AC 29-2C, are sufficient for an FBW system. Section 29.691 requires
that the flight control design allow rapid entry into autorotation
after a power failure. AC 29-2C provides that applicants may comply
with this rule through an evaluation as part of the Type Inspection
Authorization test program.
EASA requested the FAA clarify the meaning of ``normally
encountered'' in paragraph (3) of the proposed special conditions.
Specifically, EASA asked whether there are jams that are not considered
normal and are therefore excluded from the assessment. EASA further
noted that the flight conditions listed in paragraph (3) of the
proposed special conditions are contrary to the maneuvers required by
Sec. Sec. 29.141 and 29.143.
The FAA intended these special conditions to address jams
encountered during any flight condition including transitions between
flight conditions. The FAA has revised paragraph (3) accordingly.
EASA requested the FAA clarify the relationship between the
proposed special conditions and Sec. 29.685(a), which addresses flight
control jamming. EASA noted the approach in Sec. 29.685(a) is
different from the one proposed in the special conditions, as Sec.
29.685(a) requires the design of the control system to prevent jamming.
EASA states the proposed special conditions would not provide credit
for jamming that may result in a condition where continued safe flight
is guaranteed.
Section 29.685(a) contains a design requirement for mechanical
controls and is limited in scope. These special conditions are broader
and include FBW primary flight controls that did not exist when Sec.
29.685 was promulgated in 1964. Regarding EASA's statement about
credit, paragraph (3) of these special conditions require reducing
jamming in any phase of flight to a level capable of continued safe
flight and landing.
Applicability
These special conditions are applicable to the Bell Model 525
helicopter. Should Bell apply at a later date for a change to the type
certificate to include another model incorporating the same novel or
unusual design feature, these special conditions would apply to that
model as well.
Conclusion
This action affects only a certain novel or unusual design feature
on the Bell Model 525 helicopter. It is not a rule of general
applicability.
[[Page 2692]]
List of Subjects in 14 CFR Part 29
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, 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 the Bell Textron Inc. Model 525
helicopter. Unless otherwise stated, the following special conditions
will be used in lieu of Sec. 29.671(c).
The rotorcraft must be shown by analysis and tests, to be capable
of continued safe flight and landing after any of the following
failures or jamming in the flight control system for any speed or
altitude within the approved operating limitations, without requiring
exceptional piloting skill or strength. Reasonably probable failures
must have only minor effects.
(1) Any failure, excluding a jam as listed in paragraph (3).
(2) Any combination of failures not shown to be extremely
improbable, excluding a jam as listed in paragraph (3).
(3) Any jam in a control position encountered during any flight
condition, including transitions, within the approved operating
limitations, unless the jam is shown to be extremely improbable, or can
be alleviated.
Issued in Kansas City, Missouri, on January 12, 2022.
Patrick Mullen,
Manager, Technical Innovation Policy Branch, Policy and Innovation
Division, Aircraft Certification Service.
[FR Doc. 2022-00862 Filed 1-18-22; 8:45 am]
BILLING CODE 4910-13-P
