AD 2020-11-04 Issued To Mitigate Failure Of The Engine Thrust Reverser System

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.

This AD is effective June 25, 2020.

Supplementary Information: 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.

FMI: www.regulations.gov