GIV Crash Raises Questions about Gust Lock
Unwritten rules of professionalism demand that pilots and responsible media do not launch into publicly discussing suspected but unproven factors in an aircraft accident until the NTSB has issued its verdict on the probable cause. However, last month’s NTSB preliminary report on the May 31 crash of a Gulfstream IV at Hanscom Field near Boston–a report issued on the basis of information extracted from the jet’s cockpit voice recorder (CVR) and flight data recorder (FDR)–raised questions about specifics and ignited public discussion on forums and on AIN’s own website about both the airplane and the standard operating procedures (SOP) of those who fly it. A number of experienced GIV pilots offered AIN a look inside the aircraft and their company’s procedures, and all requested anonymity.
The Part 91 Gulfstream was departing Bedford Hanscom Field at 9:40 p.m. on an IFR flight plan to Atlantic City N.J., with three crew and four passengers on board. During its takeoff roll on Hanscom’s Runway 11, the jet reached a speed of 165 knots but never became airborne. At some point, the crew became aware of and discussed control problems before attempting to stop the aircraft by applying full braking and maximum reverse thrust.
The last airspeed recorded by the FDR was 100 knots. Investigators assume that is the point at which the aircraft went off the end of the pavement “onto a runway safety area, and then on to grass…where it struck approach lighting and a localizer antenna assembly, before coming to rest in a gully…about 1,850 feet from the end of the runway. A post-crash fire consumed a majority of the airplane aft of the cockpit.” All seven people aboard perished in the accident.
NTSB investigators reported a number of apparent inconsistencies in the aircraft’s operation. They found that while the flap handle in the cockpit was set to the “flaps 10” position, the FDR indicated the flaps were set to the “flaps 20” position.
Investigators also focused on the position of the aircraft’s control gust lock before takeoff: “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.” TheGIV’s internal control lock will not normally allow the thrust levers to be advanced beyond 6-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,” investigators concluded. The FDR did not, however, record any movement of the GIV’s flight controls by the crew before takeoff.
One of the GIV pilots AIN spoke with said, “The position of the controls recorded by the FDR was pretty consistent with where the [GIV’s] flight controls normally rest during taxiing. On this basis, the gust-lock theory would seem less plausible, especially since you normally don’t even start the engines with the control lock in place.” He explained that part of the Gulfstream takeoff procedure includes verifying that the controls lighten, or float, 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 said, 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 165 knots before the crew aborted thetakeoff.
Another GIV pilot told AIN, “Our SOPs say DO NOT start the engines with the control lock on.” While the engines can be cranked with the locks in place, this pilot warned that if the engines were started that way, the safest next step would be to shut down both engines and begin again. He recommended against attempting to disconnect the control lock once the engines are turning. When questioned about accidental engagement of the locks, this pilot said, “Engaging the control lock is not a casual maneuver. It takes effort.”
Gulfstream declined to answer AIN’s questions about the GIV, citing the ongoing NTSB investigation. The company did issue a maintenance and operations letter to all owners on June 13 that said, “Gulfstream is issuing this maintenance and operations letter (MOL) to remind flight crews of the importance of adhering to flight procedures published in applicable Airplane Flight Manuals (AFM) to confirm flight-control integrity and freedom of motion. Flight crews are reminded to perform the following as set forth in the applicable AFM procedures for each model aircraft: ensure the gust lock is OFF prior to starting engines (not applicable for G650); check flight controls for freedom and correct movement prior to taxi/takeoff; confirm the elevators are free during the takeoff roll.”