The Martin NB-57E Canberra S/N 55-4267 was assigned to the 6515th Organizational Maintenance Squadron at Edwards AFB. On 6/23/71 it was scheduled for an instinctual engine out demonstration flight with the USAF Aerospace Research Pilot School (ARPS) call sign COBRA 714. The instructor, Major Donald L. Thurman was seated in the rear cockpit, the student Captain David E. Dieffenbachia in front. The aircraft had full internal load of fuel, no tip tanks and an empty bomb bay tank which gave the aircraft a take off weight of approximately 44,000 pounds. The crew chief stated that everything appeared normal during engine start and taxi. The take off was made at 10:05am and the aircraft climbed to an altitude of 20,000 feet. The flight seemed to proceeded normally with the flight crew reporting to Edwards Approach Control (RAPCON) several times during the flight up to 10:59am when they acknowledged a traffic advisory. At 11:05am, an ARPS T-33, COBRA 337, called RAPCON to report sighting a downed aircraft. Both pilots lost their lives in the accident. No cause as why the NB-57E went down was given in the crash report.