Air Force officials release Predator accident report Published July 13, 2009 LANGLEY AIR FORCE BASE, Va. (AFNS) -- Air Force officials here announced an MQ-1 Predator that crashed just short of Ali Base, Iraq, Oct. 19, 2008, was due to a quill shaft bearing failure, according to an Air Combat Command Accident Investigation Board report released July 13 here. The $3.7 million Predator, assigned to the 432nd Wing at Creech Air Force Base, Nev., was destroyed upon impact. There were no injuries or damage to other property or equipment. The accident was caused by a quill shaft bearing failure that caused the variable pitch propeller to change pitch during flight to the point of producing reverse thrust. The quill shaft bearing failure was attributed to the use of a worn bearing installation tool worn used beyond the designed specifications during installation. The quill shaft is the control shaft for the variable pitch propeller. Moving the quill shaft inward or outward changes the pitch of the propeller blade, thereby changing the amount of thrust provided. A variable pitch propeller adjusts an aircraft to the pitch of the propeller during flight in order to maximize efficiency.