DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2019-0204; Project Identifier 2018-CE-042-AD; Amendment
39-21129; AD 2020-11-04]
RIN 2120-AA64

Airworthiness Directives; Learjet Inc. Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for
certain Learjet Inc. Model 60 airplanes. This AD was prompted by a
report of a reverse thrust command accelerating the airplane instead of
decelerating the airplane. The acceleration with reverse thrust
commanded occurred when the thrust reverser doors were in the stowed
position instead of the deployed position. This AD requires installing
a thrust reverser (T/R) Voice Command Warning System (VCWS) to alert
the crew of a T/R malfunction. The FAA is issuing this AD to address the
unsafe condition on these products.

DATES: This AD is effective June 25, 2020.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of June 25,
2020.

ADDRESSES: For service information identified in this final rule,
contact Learjet Inc., MS 53, P.O. Box 7707, Wichita, Kansas 67277-7707;
telephone: (toll free) 1-866-538-1247; (514) 855-2999; internet:
https://my.businessaircraft.bombardier.com. You may view this service
information at the FAA, Airworthiness Products Section, Operational
Safety Branch, 901 Locust, Kansas City, Missouri 64106. For information
on the availability of this material at the FAA, call (816) 329-4148.
It is also available on the internet at https://www.regulations.gov by
searching for and locating Docket No. FAA-2019-0204.

Examining the AD Docket

You may examine the AD docket on the internet at https://www.regulations.
gov by searching for and locating Docket No. FAA-2019-
0204; 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 other information. The
address for Docket Operations is Docket Operations, U.S. Department of
Transportation, Docket Operations, M-30, West Building Ground Floor,
Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: James Galstad, Aerospace Engineer,
Wichita ACO Branch, 1801 Airport Road, Room 100, Wichita, Kansas 67209;
telephone: (316) 946-4135; fax: (316) 946-4107; email:
james.galstad@faa.gov or Wichita-COS@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 by adding an AD that would apply to certain serial-numbered
Learjet Inc. Model 60 airplanes. The NPRM published in the Federal
Register on May 13, 2019 (84 FR 20823). The NPRM was prompted by a
report of a high-speed rejected takeoff involving a Learjet Model 60
airplane that occurred when all four main landing gear (MLG) tires blew
out during the takeoff roll. The tires blew out due to internal heat
damage consistent with under-inflation, overloading, or a combination
of both. Subsequently, damage from tires caused damage to various
components, including the MLG squat switches, brake hydraulic tubes,
wheel speed sensor wiring, and anti-skid components. In the event of
squat switch wiring failures, thrust reverser operation can be
adversely affected. During the subject accident, forward thrust
occurred when the thrust reverser doors stowed due to the failure, and
at the same time the crew was still commanding reverse thrust. Squat
switch wiring can also be damaged by other external factors, such as
bird strikes or deer strikes.
The FAA considers this AD to be the third of three related ADs that
collectively address unsafe conditions that might result from damage to
critical components on the landing gear or in the wheel well that
affect the braking, spoiler, and thrust reverser systems. AD 2010-11-
11, Amendment 39-16316 (75 FR 32255, June 8, 2010) was issued to
prevent tire failure, and AD 2013-13-09, Amendment 39-17497 (78 FR
39574, July 2, 2013) was issued to prevent failure of the braking
system or adverse operation of the spoiler and reverse thruster system
due to external damage, particularly from tire failure, which could
result in loss of control of the airplane.
The NPRM proposed to require installing a T/R VCWS to alert the
crew of a T/R malfunction. The FAA is issuing this AD to mitigate
failure of the engine thrust reverser system. The unsafe condition, if
not addressed, could result in the airplane overrunning the runway or a
runway excursion.

Comments

The FAA gave the public the opportunity to participate in
developing this final rule. The following presents the comments
received on the NPRM and the FAA's response to each comment.

Support for the NPRM

The National Transportation Safety Board (NTSB) and Damian Palaich
expressed support for the NPRM.

Request To Withdraw the NPRM

Charles Perrigoue requested that the NPRM be withdrawn. The
commenter noted that modern aircraft designs have shifted away from a
multitude of aural alarms and warnings and that most modern business
jets and airline aircraft suppress alarms during critical phases of
flight. The commenter stated there is no nexus between the proposed AD
actions and the precipitating Learjet Model 60 accident, as the pilot
correctly recognized and reacted to the thrust reverser malfunction.
The FAA disagrees with the commenter's request. The design change
required by paragraph (g) of this AD incorporates a direct aural voice
command for a rapid effective response and design features to minimize
faulty voice commands. The FAA's evaluation concludes that the
installation of the T/R VCWS required by this AD will effectively
mitigate the identified unsafe condition and prevent future scenarios
similar to the September 19, 2008, accident involving a Learjet Model
60 airplane. The T/R VCWS is monitoring the thrust reversers and
providing a voice command, when needed, which will enable a faster
pilot response to decelerate the airplane. The FAA has not changed this
AD in this regard.

Request To Incorporate a Solution That Is Not Reliant on Crew Action

An anonymous commenter stated the proposed AD does not eliminate
the root cause of the unsafe condition. The commenter further suggested
that relying on pilot response to address a catastrophic hazard is not
always valid. The commenter stated that a design solution is available
that would eliminate the uncontrollable high thrust condition. The
commenter asserted that the FAA's proposed AD contradicts its guidance
in draft advisory circular (AC) AC 25.901-2X. The acceptable design
solution suggested by the commenter is a similar installation on
another aircraft identified in the NTSB investigation report (NTSB/AAR-
10/02) and addressed through AD 2016-13-13, Amendment 18577 (81 FR
44494, July 8, 2016) (``AD 2016-13-13''). The commenter noted that AD
2016-13-13 requires installation of a control system modification that,
following a single failure cause, prevents uncontrolled high failure
thrust from occurring and prevents the engine from accelerating above
idle. The commenter further stated that Draft AC 25.901-2X identified
that assuming a crew response to address a hazard is not proper.
The FAA infers that the commenter is requesting corrective action
that does not rely on crew action, similar to the modification required
by AD 2016-13-13. The FAA acknowledges that Draft AC 25.901-2X suggests
that relying on pilot response to address a catastrophic hazard is not
always feasible; however, Draft AC 25.901-2X is not current agency
guidance because it has not yet been finalized and issued. In addition,
the FAA has determined that in some cases, including this one, relying
on pilot response to address a hazard is
appropriate. The installation of a T/R VCWS and performance of a
functional test, as required by paragraph (g) of this AD, adequately
addresses the unsafe condition on the affected airplanes. The T/R VCWS
monitors the thrust reversers and provides voice command when needed,
which will enable a faster pilot response to decelerate the airplane.
However, if the FAA obtains and analyzes additional data that indicates
the unsafe condition has not been adequately addressed by this AD, the
FAA will consider further rulemaking. The FAA has not changed this AD
in this regard.

Request To Shorten the Compliance Time

The NTSB requested that the FAA shorten the proposed compliance
time of 1,200 hours time-in-service or 48 months, because of how much
time has passed since the NTSB's July 17, 2009, safety recommendation
regarding this issue.
The FAA disagrees with the commenter's request. Based on the FAA's
risk assessment, the FAA has determined that the proposed compliance
time in this AD is adequate to address the unsafe condition. In
developing an appropriate compliance time for this action, the agency
considered the urgency associated with the unsafe condition and the
practical aspects of accomplishing the required modification within a
period of time that corresponds to the normal scheduled maintenance for
most affected owners/operators. The FAA has not changed this AD in this
regard.

Conclusion

The FAA reviewed the relevant data, considered the comments
received, and determined that air safety and the public interest
require adopting this final rule as proposed except for minor editorial
changes. The FAA has determined that these minor changes:
Are consistent with what was proposed in the NPRM for
addressing the unsafe condition; and
Do not add any burden upon the public than was proposed in
the NPRM.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Bombardier Learjet 60 Service Bulletin SB 60-78-9,
dated June 25, 2018. This service information contains procedures for
installing a T/R VCWS to alert the pilot of a T/R malfunction. This
service information is reasonably available because the interested
parties have access to it through their normal course of business or by
the means identified in the ADDRESSES section.

Costs of Compliance

The FAA estimates that this AD affects 289 airplanes of U.S.
registry.
The FAA estimates the following costs to comply with this AD:

Estimated Costs

According to the manufacturer, some of the costs of this AD may be
covered under warranty, thereby reducing the cost impact on affected
individuals. The FAA does not control warranty coverage for affected
individuals. As a result, the FAA has included all costs in this cost
estimate.

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to
issue rules on aviation safety. Subtitle I, section 106, describes the
authority of the FAA Administrator. Subtitle VII: Aviation Programs,
describes in more detail the scope of the Agency's authority.
The FAA is issuing this rulemaking under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701: General requirements.
Under that section, Congress charges the FAA with promoting safe flight
of civil aircraft in air commerce by prescribing regulations for
practices, methods, and procedures the Administrator finds necessary
for safety in air commerce. This regulation is within the scope of that
authority because it addresses an unsafe condition that is likely to
exist or develop on products identified in this rulemaking action.

Regulatory Findings

This AD will not have federalism implications under Executive Order
13132. This AD will not have a substantial direct effect on the States,
on the relationship between the national government and the States, or
on the distribution of power and responsibilities among the various
levels of government.
For the reasons discussed above, I certify that this AD:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866,
(2) Will not affect intrastate aviation in, and
(3) Will not have a significant economic impact, positive or
negative, on a substantial number of small entities under the criteria
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.

Adoption of the Amendment

Accordingly, under the authority delegated to me by the
Administrator, the FAA amends 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. The FAA amends Sec. 39.13 by adding the following new airworthiness
directive (AD):