The conventional thinking before the accident, at least at Gulfstream, was that CLmax would not change due to ground effect, and that an AOA reduction for IGE operations of 1.6 deg. compared to the stall AOA for OGE operations was adequate. As a result, the wing was physically stalling at an AOA as low as 11.2 deg. though the stickshaker was not programmed to activate until above 12 deg. AOA. Without increasing takeoff speed, a reduced CLmax would require a higher pitch angle to achieve the same lift, further eroding the stall margin.
Of the 10 NTSB recommendations, five were issued to the FAA and three to the Flight Test Safety Committee (FTSC), an international flight-test safety advocacy organization operating under the auspices of the Society of Experimental Test Pilots.
The NTSB is asking the FAA to inform domestic and foreign airframers “about the circumstances of this accident,” and to advise them to consider the possibility that an aircraft's maximum lift coefficient in ground effect could be, in contrast to common belief and practice, lower than its maximum lift coefficient at altitude, a finding made by Gulfstream in its post-crash analysis.
The board is also asking the FAA to work with the FTSC to issue updated operating flight-test guidance to manufacturers, based on the report, and develop flight-test safety guidelines based on best practices in aviation safety management.
Only two recommendations were addressed to Gulfstream, one of which is to commission an audit by qualified safety experts before its next flight-test campaign is launched, focusing on weaknesses brought out in the NTSB report.
“We recognize the safety actions they took [after] the accident,” says Deborah Hersman, NTSB chairman. “They recognized that many changes needed to be made, and that is why we don't have as many actions to them as we could have.”
The airframer, in a May 2012 submission to the NTSB, accepted responsibility for the accident and detailed a host of changes being made to address the issues raised, including the creation of an Aviation Safety Officer position, reporting directly to the company's president.
Gulfstream, as of July, continued to report a five-year backlog for the G650, with plans to deliver 24 green and 17 completed aircraft by year-end.