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FAA AD on gust lock modification on Gulfstream G-IV jets becomes effective
2 August 2017

The G-IV accident that prompted the AD (NTSB)

An FAA Airworthiness Directive (AD) is becoming effective on August 3, 2017, calling for a retrofit of the gust lock throttle interlock on specific Gulfstream G-IV, G300 and G400 jets. This AD follows a fatal accident in 2014.

On May 31, 2014 a Gulfstream G-IV corporate jet was destroyed in a takeoff accident at Bedford-Hanscom Field, Massachusetts, USA. All four passengers and three crew members were killed.
During the engine start process, the flight crew neglected to disengage the airplane’s gust lock system, which locks the elevator, ailerons, and rudder while the airplane is parked to protect them against wind gust loads. Further, before initiating takeoff, the pilots neglected to perform a flight control check that would have alerted them of the locked flight controls. During takeoff the flight crew noticed that the controls were locked. The aircraft overran the runway, struck lights and came to rest in a gully.

The G-IV is equipped with a mechanical interlock between the gust lock handle and the throttle levers that restricts the movement of the throttle levers when the gust lock handle is in the ON position. This interlock mechanism was intended to limit throttle lever movement to a throttle lever angle (TLA) of no greater than 6° during operation with the gust lock on. However, postaccident testing on nine in-service G-IV airplanes found that, with the gust lock handle in the ON position, the forward throttle lever movement that could be achieved on the G-IV was 3 to 4 times greater than the intended TLA of 6°.

This caused the NTSB to issue a Safety Recommendation (A-15-31) in September 2015, addressed to the FAA:

After Gulfstream Aerospace Corporation develops a modification of the G-IV gust lock/throttle lever interlock, require that the gust lock system on all existing G-IV airplanes be retrofitted to comply with the certification requirement that the gust lock physically limit the operation of the airplane so that the pilot receives an unmistakable warning at the start of takeoff.

A notice of proposed rulemaking (NPRM) was published by the FAA in December 2016, resulting in the AD to be published June 29, 2017. This AD now becomes effective.

Operators must, within 36 months, modify the gust lock system by doing a retrofit of the gust lock throttle interlock, in accordance with the Accomplishment Instructions provided by Gulfstream.

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