Preliminary GIV Crash Report Focuses on Flaps and Gust Lock

 - June 16, 2014, 1:30 PM

The NTSB’s preliminary report into the crash of a Gulfstream IV during takeoff roll at Bedford Hanscom Field near Boston on May 31 revealed a number of inconsistencies. On June 13, investigators reported that while the flap handle on the jet was set to the “flaps 10” position, the flight data recorder indicated the flaps were set to the “flaps 20” position.

Speculation also focused on the position of the aircraft’s gust lock before takeoff. On that subject, the report said, “The flight data recorder (FDR) data revealed the elevator control surface position during the taxi and takeoff was consistent with its position if the gust lock was engaged.” The GIV’s control lock will not normally allow the thrust levers to be advanced beyond six-percent thrust with the lock engaged. “The gust lock handle, located on the right side of the control pedestal, was however found in the forward (OFF) position and the elevator gust lock latch was disengaged,” concluded investigators. The Gulfstream’s FDR did not record any movement of the flight controls by the crew before takeoff.

AIN spoke with a GIV pilot based in the northeast U.S. who did not wish to be identified but offered some insights on the aircraft. “The position of the controls recorded by the FDR was pretty consistent with where the flight controls normally rest during taxiing,” he said. On this basis, the gust lock theory would seem less plausible.

“You normally don’t even start the engines with the control lock in place,” the pilot added. He explained that part of the Gulfstream takeoff procedure includes feeling the controls lighten as air moves across the tail surfaces early in the takeoff roll. “If we don’t feel that by 60 knots or so, it’s an automatic abort,” he added, while also questioning the takeoff speeds mentioned in the report. “At a light [takeoff] weight, the V1 speed of the GIV should have been about 118 knots,” he said, “with rotation at about 124.” This prompted him to question why the aircraft reached a speed of 165 knots before the crew aborted the takeoff.


Sounds like the control lock system malfunctioned since they had the selector in the off position and the thrust levers could be moved to takeoff power?  

But why keep going about 40K beyond VR if could not rotate?  Indecision? Disbelief?  Troubleshooting? 

NTSB remarks re pilots CVR recording did not indicate if made before Hanson arrival or during Hanson TO. Nor is public info available regarding recent flight control squaks or maintenance work or MEL status.

Doubt gust locks were deliberately set. Without NTSB sharing what was actually said on CVR then most likely inter lock malfunction.

That 40 knots only takes seconds and the crew may have attempted pulling the a Flight Power Shutoff Handle after finding the elevator immovable after VR. ( per the Immovable Flight Control in QRH)

Pilots react the way they are trained. They are conditioned to react to emergency scenarios with predictable results based on many years of simulator practice & training. They are not expected to execute maneuvers contrary to how they have been trained. I.e., well after the safety speed to do so,in this case, had come & gone.
Since it was an "unfamiliar" event combined with a natural expectation that the aircraft would fly, a delay in committing to a alternative course of action would follow only after confirmation of the un-fly able condition was realized.

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