From the
NTSB Report on the G650 flight test takeoff accident at Roswell, NM on April 2, 2011:
The National Transportation Safety Board‟s (NTSB) investigation of this accident found that the airplane stalled while lifting off the ground. As a result, the NTSB examined the role of “ground effect” on the airplane‟s performance. Ground effect refers to changes in the airflow over the airplane resulting from the proximity of the airplane to the ground. Ground effect results in increased lift and reduced drag at a given angle of attack (AOA) as well as a reduction in the stall AOA. In preparing for the G650 field performance flight tests, Gulfstream considered ground effect when predicting the airplane‟s takeoff performance capability but overestimated the in - ground - effect stall AOA. Consequently, the airplane‟s AOA threshold for stick shaker (stall warning) activation and the corresponding pitch limit indicator (on the primary flight display) were set too high, and the flight crew received no tactile or visual warning before the actual stall occurred.