[Federal Register Volume 89, Number 89 (Tuesday, May 7, 2024)]
[Rules and Regulations]
[Pages 37969-37971]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-09825]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 29

[Docket No. FAA-2021-1143; Special Conditions No. 29-055-SC]


Special Conditions: Airbus Helicopters Model H160-B Helicopter; 
Extended Duration of Flight After Loss of Main Gearbox Lubrication

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Airbus Helicopters 
(Airbus) Model H160-B helicopter. This helicopter has a novel or 
unusual design feature when compared to the state of technology 
envisioned in the airworthiness standards for helicopters. This design 
feature is the extended duration of continued safe flight and landing 
beyond 30 minutes after indication to the flightcrew of the loss of 
main gearbox lubrication. 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 June 6, 2024.

FOR FURTHER INFORMATION CONTACT: Kamron Dowlatabadi, Mechanical 
Systems, AIR-623, Technical Policy Branch, Policy and Standards 
Division, Aircraft Certification Service, 10101 Hillwood Parkway, Fort 
Worth, TX 76177; telephone (817) 222-5219; email 
[email protected].

SUPPLEMENTARY INFORMATION:

Background

    On July 10, 2023, Airbus applied for an amendment to Type 
Certificate No. R00009RD for the Model H160-B helicopter to include 
continued safe flight and landing beyond 30 minutes after indication to 
the flightcrew of the loss of main gearbox lubrication.
    The Airbus Model H160-B helicopter is a transport-category, twin-
turboshaft-engine helicopter certificated under 14 CFR part 29. This 
helicopter has a maximum takeoff weight of 13,436 lbs. with seating for 
12 passengers and 2 flightcrew members. The Airbus Model H160-B 
helicopter is also characterized by the integration of composite 
materials in its airframe, five main rotor blades (Blue Edge 
technology), a Fenestron tail rotor, and a Helionix avionics suite.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Airbus must show that the 
Model H160-B helicopter meets the applicable provisions of the 
regulations listed in Type Certificate No. R00009RD, 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 (i.e., 14 CFR part 29) do not contain adequate or 
appropriate safety standards for the Airbus Model H160-B helicopter 
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 Airbus Model H160-B helicopter must comply with the 
noise certification requirements of 14 CFR part 36.
    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.  21.101.

Novel or Unusual Design Features

    The Airbus Model H160-B helicopter will incorporate the following 
novel or unusual design feature:
    Extended duration of continued safe flight and landing beyond 30 
minutes after indication to the flightcrew of the loss of main gearbox 
lubrication.

Discussion

    Current regulations do not prescribe a duration for continued safe 
flight and landing to be specifically called out in the rotorcraft 
flight manual when a loss of main gearbox lubrication is indicated to 
the flightcrew. Although Sec.  29.927(c)(1) requires a 30-minute test 
to show that the rotor drive system, which is defined in Sec.  
29.917(a) and includes the main gearbox, is operational for 30 minutes 
following the indication to the flightcrew of a loss of lubrication, 
the associated bench test conditions may not be representative of 
aircraft flight conditions because a 30-minute bench test of the main 
gearbox may not translate to 30 minutes of continued safe flight and 
landing.
    The novel or unusual design feature of the Airbus Model H160-B 
helicopter is intended to enable the helicopter to continue safe flight 
and landing, for a minimum of 30 minutes, to the intended destination 
or to a safe landing location after the indication to the flightcrew of 
a loss of main gearbox lubrication. To meet this minimum 30 minutes of 
continued safe flight and landing, the Airbus Model H160-B helicopter 
main gearbox is designed with a redundant lubrication system. This main 
gearbox redundant lubrication system would allow continued safe 
operation after the failure of a single lubrication system. Current 
regulations do not address a redundant lubrication system that allows 
operation after the failure of a single lubrication system because at 
the time the existing regulations were issued, the agency did not 
envision that a flight duration of more than 30 minutes after the 
indication to the flightcrew of the loss of main gearbox lubrication 
was needed. Accordingly, these special conditions provide testing 
criteria to ensure the reliability of the redundant lubrication system 
to provide an extended period for safe flight and landing beyond 30 
minutes after indication to the flightcrew of the loss of the main 
gearbox lubrication.
    These special conditions add new requirements in lieu of the 
existing airworthiness standards in Sec. Sec.  29.917(a) and 29.927(c) 
and add a requirement to Sec.  29.1585.
    At the time of the issuance of the existing regulations, the FAA 
did not envision the evolving operations for these types of aircraft 
and the regulations did not include the main gearbox lubrication system 
components in the required design assessment of the rotor drive system. 
Accordingly, these special conditions include requirements for 
addressing ``any associated lubrication system components including oil 
coolers'' in the design assessment required by Sec.  29.917(b).
    These special conditions add a safety margin over the current 30-
minute rotor drive system test specified in Sec.  29.927(c)(1) by 
requiring a test duration of more than 30 minutes to

[[Page 37970]]

ensure that the rotor drive gearbox system has an in-flight operational 
endurance capability of at least 30 minutes following a failure of any 
one pressurized, normal-use lubrication system. The 30-minute test 
interval starts when the lubrication-failure indication to the 
flightcrew is triggered and the engine is at maximum continuous power. 
These special conditions require a bench test of the rotor drive system 
main gearbox for a minimum of 30 minutes to establish a maximum period 
of in-flight operation following loss of main gearbox lubrication, and 
to ensure that the main gearbox continues to operate safely for at 
least 30 minutes after an indication to the flightcrew of a loss of 
lubrication.
    The term ``confidence'' specified in Category A and B in these 
special conditions necessitates the applicant provide supporting data 
with respect to the mechanical behavior of the main gearbox and must 
reflect the applicant's confidence in the repeatability of the 
certification test data. Test loading, in the context of these special 
conditions, refers to the engine, main gearbox, clutch system, and 
rotors (or similar test apparatus) interconnected and operating in 
unison, as this combination of mechanical elements pertains to power 
input transmitted to the main gearbox and subsequent reaction torques 
simulating operating conditions.
    These special conditions add a requirement that the maximum 
duration of operation after a failure, which results in a loss of main 
gearbox lubrication and an associated indication to the flightcrew, 
must be furnished in the rotorcraft flight manual, and the duration 
must not exceed the maximum period of in-flight operational endurance 
capability substantiated.
    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. 29-21-01-
SC for the Airbus Model H160-B helicopter, which was published in the 
Federal Register on May 12, 2023 (88 FR 30680). The FAA received 
several comments from Leonardo Helicopters regarding the proposed 
special conditions.
    Leonardo Helicopters requested the FAA generally maintain 
harmonization and alignment with the EASA certification specifications 
(CS) 29 requirements by implementing the same changes to part 29 that 
were introduced by EASA rulemaking task RMT.0608, following notice of 
proposed amendment (NPA) 2017-07, Rotorcraft gearbox loss of 
lubrication, through Amendment 5.
    This request relating to the pursuit of future rulemaking for part 
29 is beyond the scope of these special conditions. No change was made 
to these special conditions as a result of this comment.
    Leonardo Helicopters stated that EASA's CS-29 requirements and 
acceptable means of compliance (AMC) clearly define how to establish 
the operational endurance capability through the application of 
reduction factors. However, the correlation between 30 and 60 minutes, 
and the criteria for defining this correlation, is not clear in the 
proposed special conditions. Leonardo Helicopters requested the FAA 
revise the proposed special conditions to define the proposed reduction 
factors and allow the public to comment. The FAA infers that Leonardo 
Helicopters is also requesting clarification regarding the correlation 
between 30 and 60 minutes for the bench test.
    The FAA disagrees with the commenter's request to include reduction 
factors and related material in these special conditions. The FAA 
considers the details referenced by Leonardo Helicopters, including the 
correlation between the test duration and substantiated safe operation 
duration, to be related to the means of compliance for these special 
conditions. Means of compliance for these special conditions are 
defined separately between the FAA and the applicant via the FAA issue 
paper process, which is outside the scope of these special conditions. 
However, to address the Leonardo Helicopters comment, the FAA has 
clarified language in the discussion section. Specifically, the FAA 
removed the previous reference in these special conditions to a 60-
minute bench test scenario, since it is not a requirement under 
29.927(c), but rather an example to illustrate how applicants translate 
the time duration of a bench test into 30 minutes of substantiated 
operation for continued safe flight and landing. In addition, the term 
``reduction factor'' has been removed from the discussion section and 
replaced with language to define the term ``confidence'' used in these 
special conditions.
    Additionally, Leonardo Helicopters stated that EASA CS-29 does not 
have a similar requirement for a test duration of at least 60 minutes, 
and therefore the special conditions are not harmonized with the EASA 
requirements. The FAA infers Leonardo Helicopters is requesting that 
the FAA revise the proposed special conditions to address an alleged 
contradiction and lack of harmonization with the related EASA CS-29 
requirements.
    The FAA does not agree to revise the proposed special conditions to 
address a possible contradiction because the FAA does not find that a 
contradiction exists. The commenter suggests that these special 
conditions contain a 60-minute testing requirement. There is no 
specific requirement in these special conditions for a 60-minute test. 
However, in the preamble of the proposed special conditions, the FAA 
discussed a scenario where it may be necessary for an applicant to 
perform a 60-minute test, depending on reduction factors. As explained 
previously, this language has been removed to address the related 
public comment and replaced with language to describe the context of 
the word ``confidence'' used in these special conditions. The details 
related to the test duration and maximum period of in-flight operation 
following loss of main gearbox lubrication are associated with the 
means of compliance for these special conditions. As previously 
explained, the means of compliance are established between the FAA and 
applicant through the FAA issue paper process and the FAA's acceptance 
of a specific means of compliance is beyond the scope of these special 
conditions. No changes were made to these special conditions as a 
result of this comment. However, the FAA has made minor editorial 
changes to these special conditions to ensure consistency in the 
language of the requirements.

Applicability

    As discussed above, these special conditions are applicable to the 
Airbus Helicopters Model H160-B helicopter. Should Airbus Helicopters 
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 one model of helicopter. It is not a rule of general applicability.

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:


[[Page 37971]]


    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 Airbus Helicopters Model H160-B 
helicopter. Unless stated otherwise, all requirements in Sec. Sec.  
29.917, 29.927, and 29.1585 still apply.
    In lieu of Sec.  29.917(a), the following special condition 
applies:
    (a) Design: General. The rotor drive system includes any part 
necessary to transmit power from the engines to the rotor hubs. This 
includes gearboxes, shafting, universal joints, couplings, rotor brake 
assemblies, clutches, supporting bearings for shafting, any attendant 
accessory pads or drives, any cooling fans, and any associated 
lubrication-system components including oil coolers that are a part of, 
attached to, or mounted on the rotor drive gearbox system.
    In lieu of Sec.  29.927(c), the following special condition 
applies:
    (c) Lubrication system failure. For rotor drive gearbox systems 
featuring a pressurized, normal-use lubrication system, the following 
requirements for continued safe flight and landing apply:
    (1) Category A. Confidence must be established that the rotor drive 
gearbox system has an in-flight operational endurance capability of at 
least 30 minutes following a failure of any one pressurized, normal-use 
lubrication system.
    (i) For each rotor drive gearbox system necessary for continued 
safe flight or safe landing, the applicant must conduct a test that 
simulates the effect of the most severe failure mode of the 
pressurized, normal-use lubrication system, as determined by the 
failure analysis required by Sec.  29.917(b). The duration of the test 
must be dependent on the number of tests and the component condition 
after each test.
    (ii) The test must begin when the indication to the flightcrew 
shows a lubrication failure has occurred, and its loading must be 
consistent with 1 minute at maximum continuous power, followed by the 
minimum power needed for continued flight at the rotorcraft maximum 
gross weight.
    (iii) The test must end with a 45-second out-of-ground-effect (OGE) 
hover to simulate a landing phase. Test results must substantiate the 
maximum period of operation following a loss of lubrication by means of 
an extended test duration or multiple test specimens, or another 
approach prescribed by the applicant and accepted by the FAA.
    (2) Category B. Confidence must be established that the rotor drive 
gearbox system has an in-flight operational endurance capability to 
complete an autorotation descent and landing following a failure of any 
one pressurized, normal-use lubrication system.
    (i) For each rotor drive gearbox system necessary for safe 
autorotation descent or safe landing, the applicant must conduct a test 
of at least 16 minutes and 15 seconds, following the most severe 
failure mode of the pressurized, normal-use lubrication system, as 
determined by the failure analysis required by Sec.  29.917(b).
    (ii) The test must begin when the indication to the flightcrew 
shows that a lubrication failure has occurred, and its loading must be 
consistent with 1 minute at maximum continuous power. Thereafter, the 
input torque should be reduced to simulate autorotation for a minimum 
of 15 minutes.
    (iii) The test must be conducted using an input torque to simulate 
a minimum power landing for approximately 15 seconds.
    In addition to Sec.  29.1585, the following special condition 
applies:
    (h) Power Plant limitations. The maximum duration of operation 
after a failure, resulting in any loss of lubrication of a rotor-drive-
system gearbox and an associated oil-pressure warning, must be 
furnished in the rotorcraft flight manual, and must not exceed the 
maximum period substantiated in accordance with Sec.  29.927(c) of 
these special conditions.

    Issued in Kansas City, Missouri, on April 29, 2024.
Patrick R. Mullen,
Manager, Technical Policy Branch, Policy and Standards Division, 
Aircraft Certification Service.
[FR Doc. 2024-09825 Filed 5-6-24; 8:45 am]
BILLING CODE 4910-13-P