Initial reports into a 31 May fatal Gulfstream GIV crash in Bedford, Massachusetts has led the airframer to issue a service bulletin warning pilots to ensure the flying control gust locks are not engaged before the start of the take-off run.
The US National Transportation Safety Board says the aircraft failed to take off at Bedford, overrunning the end of the runway into a gulley and killing all six people on board.
The jet’s gust locks were found to be disengaged, but it is believed during the take-off run they were engaged. This locks the elevator in the down position, and the rest of the flying controls in a neutral position.
The NTSB says the gust locks are supposed to be disengaged before engine start. As the engines run the hydraulics power up, and it becomes difficult to disengage the mechanical locks.
The NTSB’s recommendation is to shut the engines down, disengage the gust locks and restart. The controls are then to be checked for full and free movement, with another such check just before take-off.
The NTSB says the GIV’s flight data recorder shows no attempt to check control movement, but the flaps were correctly set for take-off and the engines operating according to the power lever position.
The calls for V1 and rotate were normal, but after the rotate calls the cockpit voice recorder “captured comments concerning aircraft control”, the NTSB says.
The GIV has an embedded interlock system to prevent the throttles being advanced beyond 6% when the gust locks are still engaged. However, it has been discovered that under certain circumstances the throttles can be advanced to take-off power with the gust locks still engaged.
There is question as to whether the gust lock handle was forced into the “off” position with the engines running. The NTSB says: “The gust lock handle, located on the right side of the control pedestal, was found in the forward (OFF) position, and the elevator gust lock latch was found not engaged.”
The investigation is ongoing, and Gulfstream says it is not clear whether the appropriate reaction is for the company to make design changes or modify procedures.