Incident
The aircraft, a KC-135 tanker registered as 56-3599, was operating a special flight from Westover Air Force Base in Massachusetts to RAF Brize Norton in the United Kingdom. On board were seven crew members and eight American journalists who had been covering the first transatlantic flight of a KC-135. Two other similar aircraft had departed earlier; 56-3599 was the third in a series of four scheduled flights.
During takeoff from runway 23, the aircraft encountered serious difficulties gaining altitude. Shortly after liftoff, the right wing struck trees, and the aircraft then hit power cables before crashing in a massive explosion on a Massachusetts highway approximately 1,000 yards past the end of the runway. The aircraft disintegrated on impact, and all 15 occupants were killed.
Investigation
The official investigation determined that the aircraft's flaps were deployed at an incorrect angle of 40° for takeoff. This incorrect flaps setting, combined with the aircraft's heavy load and the relatively high ambient temperature, reduced the aircraft's performance. The investigation also noted that at the time of the accident, visibility was estimated at 2.5 kilometers due to nighttime conditions and a low ceiling. No mechanical failure or in-flight fire occurred prior to the final impact.
Probable Cause
The probable cause of the accident was the deployment of flaps at a wrong angle of 40° at takeoff. The combination of a wrong flaps setting with a heavily loaded aircraft and relative high temperature reduced the aircraft's performance. Visibility was estimated at 2.5 km due to night and low ceiling. No mechanical failure or in-flight fire occurred prior to final impact.