Accident Boeing EC-135N 61-0328,

ASN Wikibase Occurrence # 328102

Date:	Wednesday 6 May 1981
Time:	10:50
Type:	Boeing EC-135N
Owner/operator:	United States Air Force - USAF
Registration:	61-0328
MSN:	18235/C13
Year of manufacture:	1961
Total airframe hrs:	13471 hours
Engine model:	Pratt & Whitney TF33-PW-102
Fatalities:	Fatalities: 21 / Occupants: 21
Aircraft damage:	Destroyed, written off
Category:	Accident
Location:	3 km NNE of Walkersville, MD - United States of America
Phase:	En route
Nature:	Military
Departure airport:	Dayton-Wright Patterson AFB, OH (FFO/KFFO)
Destination airport:	Dayton-Wright Patterson AFB, OH (FFO/KFFO)
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
Boeing EC-135N aircraft 61-0328, call sign AGAR 23, was scheduled for an Advanced Range Instrumented Aircraft (ARIA) training mission out of Wright-Patterson AFB. The mission was designed provide training for the navigator and primary mission electronic equipment (PMEE) operators. On board the aircraft were 17 crewmembers and four authorized passengers. AGAR 23 departed at 10:05 and climbed to FL290, which was reached at 10:30. The aircraft commander occupied the right pilot seat and a passenger, his wife, occupied the left pilot seat.
For undetermined reasons, the aircraft pitch trim moved to the full nose-down position. The autopilot could overcome the trim until near full nose-down. The aircraft then rapidly pitched over, most likely upon release of the autopilot, and induced sufficient negative g forces to cause the generators to trip off line and loss of all AC electrical power. The pitch trim could then not be moved electrically. This condition, while unusual, can be easily controlled if prompt corrective action is taken; however, if corrective action is delayed approximately 8 sec., the aircraft pitch angle will be greater than 30 deg. nose-down and the airspeed in excess of 350 KIAS. Under these conditions, the aircraft cannot be controlled until the pitch trim is moved toward neutral. While it is clear that recovery was delayed, the reason for the delay is unknown. The aircraft became uncontrollable and entered a steep descent. The aircraft emerged from the clouds at 2,000 ft. AGL. Airspeed was in excess of 400 KTAS and dive angle was 20 to 30 deg. Engine power was above 2.0 EPR. At approximately 1,500 ft. MSL an explosion occurred inside the pressurized compartment of the fuselage and weakened the aircraft structure to the extent that catastrophic failure of the aircraft followed immediately.
The cause of this explosion was undetermined; however, the aircraft was in an unrecoverable condition at the time of the explosion and a crash was already inevitable.

Sources:

USAF Aircraft Accident Investigation (IAW AFR 110-14)

Location

Images:

photo (c) Mickey W. Sanborn, US Navy; Camp Springs-Andrews AFB, MD (ADW/KADW); 12 June 1981; (publicdomain)