The Gulfstream IV has five normal checklists to be completed by the flight crew before take-off:


"Before starting engines" checklist. "Starting engines" checklist. "After starting engines" checklist. "Taxi/before take-off" checklist. "The line-up" checklist.


The NTSB said, "Although one of the pilots could have completed one or more of these checklists silently, the pilots did not discuss or call for any of these checklists, execute any of the checklist items using standard verbal callouts, or verbally acknowledge the


completion of any of these checklists."


The CVR did not record previous flights, but the aircraft’s quick access recorder, which also survived the crash, yielded a damning parameter. On only three of the aircraft’s previous 175 take-offs had there been a full stop-to-stop control check, as required by the checklist. This was a non- compliance rate of 98 percent.


The investigation concluded that the pilots had been habitual ignorers of spoken checklists, with the senior pilot known to have memorised checklists. The crew either did not use checklists, or ran through them silently. Either way, they allowed too much opportunity for mistakes and omissions.


‘These behaviors likely resulted from a complacency that evolved over time because the two pilots flew the same airplane almost exclusively with each other over multiple years,’ the NTSB concluded, describing the phenomenon as ‘drift in parallel’.


No mechanism was in place for the company to detect this routine non-compliance. The chief pilot, whose job was to ensure compliance with the company’s exemplary written standard operating procedures (SOPs), was one of the two on the flight deck. The company did not have a flight data monitoring program, which by detecting the lack of control check movement, for example, could have pointed to a problem with SOPs. And the pilots were not regularly observed in flight by other qualified personnel.


None of this had prevented the company from successfully passing safety audits, including one from the International Business Aviation Council’s (IBAC) IS-BAO (International Standard for Business Aircraft Operations) program. The 2012 audit had verified proper checklist usage during one of the pilot’s annual proficiency checks in a simulator.


The gust lock and missed clues


The Gulfstream IV has an interlock in its gust lock system, intended to limit the operation of the throttles when the system is engaged, and thereby make take-off impossible. This should give the flight crew an unmistakable warning that the gust lock is on should the crew attempt to take off.


The interlock mechanism was intended to limit throttle lever movement to an angle of six degrees during operation with the gust lock on. However, testing on nine in-service Gulfstream IVs found throttle lever angles of up to 24.2 degrees were possible. Incorrect rigging could increase this to 26 degrees. The crashed aircraft, which had a damaged pin its gust lock handle mechanism, could achieve 27.5 degrees (out of a 58 degree normal range, or 22 degrees with an undamaged pin). This allowed the aircraft to accelerate to substantial speed, against the design’s intention, and against airworthiness regulations.


Early in the take-off run the pilot commented ‘couldn’t get it,’ which the NTSB took to be an expression of surprise at meeting the throttle lever restriction. He did not abort take-off but engaged the auto-throttle, which allowed the engines to deliver power close to the take-off setting. Speed was below 80 knots at this point.


This imperfect warning was the second indication that the gust lock had been left on. The first had been the rudder limit warning, most likely caused when an inadvertent touch of the pedal moved the rudder against the gust lock stop.


There was a third, admittedly subtle, clue that the crew did not spot. At rest, the Gulfstream’s yokes lean forward in each cockpit, but according to the handling notes used by the crew in their most recent training ‘by 80 knots, air loads will cause the yoke to move from full forward to the neutral


13 CRM 2, TEM, Fatigue


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