Special Conditions: Bell Helicopter Textron Canada Limited, Model Bell 505, Visual Flight Rules Autopilot and Stability Augmentation System (AP/SAS System)
| Published date | 19 February 2020 |
| Citation | 85 FR 9363 |
| Record Number | 2020-02741 |
| Section | Rules and Regulations |
| Court | Federal Aviation Administration |
Federal Register, Volume 85 Issue 33 (Wednesday, February 19, 2020)
[Federal Register Volume 85, Number 33 (Wednesday, February 19, 2020)]
[Rules and Regulations]
[Pages 9363-9365]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2020-02741]
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Rules and Regulations
Federal Register
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Federal Register / Vol. 85, No. 33 / Wednesday, February 19, 2020 /
Rules and Regulations
[[Page 9363]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 27
[Docket No. FAA-2019-0546; Notice No. 27-048-SC]
Special Conditions: Bell Helicopter Textron Canada Limited, Model
Bell 505, Visual Flight Rules Autopilot and Stability Augmentation
System (AP/SAS System)
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are issued for the Bell Helicopter
Textron Canada Limited (BHTCL) Bell Model 505 helicopter. This
helicopter as modified by S-TEC will have a novel or unusual design
feature associated with installation of the autopilot and stability
augmentation system (AP/SAS system). 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: These special conditions are effective February 19, 2020.
FOR FURTHER INFORMATION CONTACT: Andy Shaw, Aerospace Engineer, FAA,
Rotorcraft Standards Branch, Policy and Innovation Division, 10101
Hillwood Pkwy, Fort Worth, TX 76177; telephone (817) 222-5384; email
[email protected].
SUPPLEMENTARY INFORMATION:
Background
On January 21, 2019, S-TEC applied for a supplemental type
certificate (STC) to install an AP/SAS system on the Bell Model 505
helicopter. The Bell Model 505 helicopter is a 14 CFR part 27 normal
category, single turbine engine, conventional helicopter designed for
civil operation. This helicopter model is capable of carrying up to
four passengers with one pilot and has a maximum gross weight of up to
4,475 pounds (external loading). The major design features include a 2-
blade main rotor, an anti-torque tail rotor system, a skid landing
gear, and a visual flight rule basic avionics configuration. S-TEC
proposes to modify this model helicopter by installing an AP/SAS
system.
The AP/SAS system provides attitude stabilization in two or three
axes (pitch and roll with optional yaw) as well as higher-level
autopilot functions such as altitude hold, heading command and
navigation tracking. However, the possible failure conditions for this
system, and their effect on the continued safe flight and landing of
the helicopter, are more severe than those envisioned by the present
rules.
The effect on safety is not adequately covered under 14 CFR 27.1309
for the application of new technology and new application of standard
technology. Specifically, the present provisions of Sec. 27.1309(c) do
not adequately address the safety requirements for systems whose
failures could result in catastrophic or hazardous/severe-major failure
conditions, or for complex systems whose failures could result in major
failure conditions. The current regulations are inadequate because when
Sec. 27.1309(c) was promulgated, it was not envisioned that a normal
category rotorcraft would use systems that are complex or whose failure
could result in ``catastrophic'' or ``hazardous/severe-major'' effects
on the rotorcraft. This is particularly true with the application of
new technology, new application of standard technology, or other
applications not envisioned by the rule that affect safety. Possible
failure modes exhibited by the S-TEC AP/SAS system could result in a
catastrophic event.
Type Certification Basis
Under 14 CFR 21.101, S-TEC must show that the Bell Model 505
helicopter, as modified by the installed AP/SAS, continues to meet the
applicable regulations incorporated by reference in the Type
Certificate Number R00008RD. The regulations incorporated by reference
in the type certificate are commonly referred to as the ``original type
certification basis.'' The regulations incorporated by reference in
Type Certificate Number R00008RD are as follows:
14 CFR part 27, dated October 2, 1964, amendment 27-1 through 27-47
14 CFR part 36, amendment 36-1 through 36-30
In addition, the certification basis includes certain equivalent
level of safety findings that are not relevant to these special
conditions.
The Administrator has determined the applicable airworthiness
regulations (that is, 14 CFR part 27), as they pertain to this STC, do
not contain adequate or appropriate safety standards for the Bell Model
505 helicopter because of a novel or unusual design feature. Therefore,
special conditions are prescribed under Sec. 21.16.
Special conditions are initially applicable to the model for which
they are issued. Should S-TEC apply for an STC to modify any other
model included on the same type certificate to incorporate the same
novel or unusual design feature, the special conditions would also
apply to the other model.
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(d).
Novel or Unusual Design Features
The Bell Model 505 helicopter will incorporate the following novel
or unusual design features: AP/SAS. An autopilot (AP) is a system used
to control the trajectory of an aircraft without constant input from
the pilot. This allows the pilot to focus on other aspects of
operations such as weather and systems. A stability augmentation system
(SAS) is another type of automatic flight control system; however,
instead of maintaining the aircraft on a predetermined attitude or
flight path, the SAS will reduce pilot workload by dampening aircraft
buffeting regardless of the attitude or flight path.
Discussion
To comply with the provisions of the special conditions, the FAA
requires that S-TEC provide the FAA with a systems safety assessment
(SSA) for the final AP/SAS installation configuration that will
adequately address the safety objectives established by a functional
[[Page 9364]]
hazard assessment (FHA). This process will ensure that all failure
conditions and their resulting effects are adequately addressed for the
installed AP/SAS. The SSA process is part of the overall safety
assessment process discussed in FAA Advisory Circular 27-1B,
Certification of Normal Category Rotorcraft, and Society of Automotive
Engineers document Aerospace Recommended Practice (ARP) 4761,
Guidelines and Methods for Conducting the Safety Assessment Process on
Civil Airborne Systems and Equipment.
These special conditions require that the AP/SAS installed on a
Bell Model 505 helicopter meet the requirements to adequately address
the failure effects identified by the FHA, and subsequently verified by
the SSA, within the defined design integrity requirements.
Failure conditions are classified according to the severity of
their effects on the rotorcraft. Radio Technical Commission for
Aeronautics, Inc. (RTCA) Document DO-178C, Software Considerations in
Airborne Systems and Equipment Certification, provides software design
assurance levels most commonly used for the major, hazardous/severe-
major, and catastrophic failure condition categories. The AP/SAS system
equipment must be qualified for the expected installation environment.
The test procedures prescribed in RTCA Document DO-160G, Environmental
Conditions and Test Procedures for Airborne Equipment, are recognized
by the FAA as acceptable methodologies for finding compliance with the
environmental requirements. Equivalent environment test standards may
also be acceptable. Environmental qualification provides data to show
that the AP/SAS system can perform its intended function under the
expected operating condition. Some of the main considerations for
environmental concerns are installation locations and the resulting
exposure to environmental conditions for the AP/SAS system equipment,
including considerations for other equipment that may also be affected
environmentally by the AP/SAS equipment installation. The level of
environmental qualification must be related to the severity of the
considered failure conditions and effects on the rotorcraft.
Discussion of Comments
Notice of proposed special conditions No. 27-048-SC for the Bell
Helicopter Textron Canada Limited (BHTCL) Bell Model 505 helicopter was
published in the Federal Register on November 21, 2019 (84 FR 64233).
Comments were received from two commenters.
One commenter requested generally that the FAA broaden the scope of
the safety standards to allow for expanded technological improvements.
This commenter did not request specific changes to the proposed
document.
The FAA disagrees. The proposed special condition is not a rule of
general applicability. It affects only the model aircraft for which it
is issued. The FAA did not make any changes in response to this
comment.
Bell Textron, Inc. stated that autopilot and stability augmentation
systems are not ``novel or unusual'' design features because these
types of systems are common and have been used in helicopters for many
years.
The FAA disagrees. As explained under ``Type Certification Basis,''
the FAA issues special conditions when the conditions in Sec. 21.16
are met. Under that rule, whether a design feature is ``novel or
unusual'' is not determined by how long it has existed or how commonly
it is used. Rather, a feature is novel or usual if the applicable
airworthiness regulations do not contain adequate or appropriate safety
standards to address it. For the reasons explained under
``Background,'' current Sec. 27.1309 does not adequately address the
safety requirements for the S-TEC AP/SAS. Accordingly, this system is a
novel or unusual design feature under Sec. 21.16. The FAA did not make
any changes in response to this comment.
Bell Textron, Inc. also requested the FAA clarify the maximum gross
weight stated in the notice of proposed special conditions.
The FAA agrees and has made the requested change. These final
special conditions state that the maximum gross weight of 4,475 lbs is
for external loading.
Bell Textron, Inc. requested that the FAA add language to the
references to ARP 4754 and DO-178C stating that these documents are
acceptable methodologies for finding compliance with the applicable
requirements and equivalent methodologies may be acceptable.
The FAA agrees to clarify. The notice of proposed special condition
does not contain any reference to ARP 4754 and does not require that S-
TEC comply with RTCA DO-178C. Rather, the reference to RTCA DO-178C for
software design assurance levels is informational. S-TEC may use ARP
4754A and DO-178C or any other equivalent methodology that the FAA
finds acceptable to show compliance. The FAA did not make any changes
in response to this comment.
Lastly, Bell Textron, Inc. requested the FAA clarify whether Policy
Statement PS-ASW-27-15 can be applied in this application.
The FAA agrees to clarify. FAA Policy Statement PS-ASE-27-15 may be
used by S-TEC in showing compliance with this special condition. The
FAA did not make any changes in response to this comment.
Applicability
These special conditions are applicable to the S-TEC AP/SAS
installed as an STC approval in Bell Model 505 helicopters, Type
Certificate Number R00008RD.
Conclusion
This action affects only certain novel or unusual design features
for an S-TEC AP/SAS STC installed on one model helicopter. It is not a
rule of general applicability and affects only the applicant who
applied to the FAA for approval of these features.
List of Subjects in 14 CFR Part 27
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, 44704.
The Special Conditions
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special conditions are part of the S-TEC
supplemental type certification basis for installation of an autopilot/
stabilization augmentation system (AP/SAS) system on Bell Model 505
helicopters.
Instead of the requirements of 14 CFR 27.1309(b) and (c), the
following must be met for certification of the AP/SAS system installed
on Bell Model 505 helicopters:
a. The equipment and systems must be designed and installed so that
any equipment and systems do not adversely affect the safety of the
rotorcraft or its occupants.
b. The rotorcraft systems and associated components considered
separately and in relation to others systems, must be designed and
installed so that:
(1) The occurrence of any catastrophic failure condition is
extremely improbable;
(2) The occurrence of any hazardous failure condition is extremely
remote; and
(3) The occurrence of any major failure condition is remote.
c. Information concerning an unsafe system operating condition must
be provided in a timely manner to the crew to enable them to take
appropriate
[[Page 9365]]
corrective action. An appropriate alert must be provided if immediate
pilot awareness and immediate or subsequent corrective action is
required. Systems and controls, including indications and
annunciations, must be designed to minimize crew errors which could
create additional hazards.
Issued in Fort Worth, Texas, on January 30, 2020.
Stephen Barbini,
Acting Manager, Rotorcraft Standards Branch, Policy and Innovation
Division, Aircraft Certification Service.
[FR Doc. 2020-02741 Filed 2-18-20; 8:45 am]
BILLING CODE 4910-13-P
