Gulfstream IV Crash Mystery Focuses on Mechanical Systems

Gulfstream IV’s tire tracks

Accident investigators are focusing on two perplexing clues as they try to determine what caused the deadly crash of Gulfstream IV in Bedford, Massachusetts, on May 31 after the jet failed to lift off from the runway during what should have been a routine takeoff.

The first mystery concerns the GIV’s flaps. Investigators found the flap handle in the cockpit in the 10-degree detent, yet a review of flight data recorder information shows the flaps were set by the crew to 20 degrees before takeoff.

Another possible clue concerns the GIV’s mechanical gust lock system, which can be set with a handle in the cockpit. The device locks the aileron and rudder in the neutral position and the elevator in the down position to protect the control surfaces from wind gusts while parked.

Although the gust lock handle in the cockpit was found in the off position and the gust lock latch was disengaged, FDR data shows the elevator was deflected downward during taxi and takeoff, as if the gust lock was engaged.

The National Transportation Safety Board noted in its preliminary report on the accident that a mechanical interlock system should prevent the throttle from advancing beyond 6 percent with the gust lock engaged. At no point before the takeoff did the pilots perform a control check, according to FDR data.

The GIV reached a high speed during the takeoff roll from Hanscom Field’s 7,011-foot Runway 11. One of the pilots can be heard calling out “V1” and “rotate” but the jet’s nose fails to rise. The pilots discuss a control problem as the thrust reversers and heavy braking are applied.

The jet reached a maximum speed of 165 knots and had slowed to about 100 knots when it careened off the end of the runway. The airplane continued another 1,850 feet before crashing into a gully and catching fire. The pilots, flight attendant and three passengers were killed.

The NTSB says the investigation will next focus on the wreckage and the GIV’s mechanical systems.

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