[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
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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