Departure and Initial Flight
Zantop Flight 931 was loaded with cargo at 00:40, with all cargo bulk loaded and tied down on the right side of the airplane for the full length of the cargo compartment. The flight departed the gate at Baltimore/Washington International Airport at 01:05 and took off on runway 28 at 01:10. At 01:11:42, the flight contacted Baltimore departure control and was cleared to 13,000 feet. After switching to Washington ARTCC, the flight was cleared further to flight level 220.
Gyro Malfunction
At 01:32, a No. 2 gyro malfunction prompted the crew to select the No. 1 gyro to drive both approach horizons, and the problem appeared resolved. At 01:43:09, Cleveland ARTCC cleared Flight 931 direct to the Dryer VOR. After the turn to the Dryer VOR, the first officer’s approach horizon may have displayed incorrect pitch and roll information. The flightcrew may have received conflicting pitch and roll information from the two approach horizons as they attempted to recover from an unusual attitude.
Loss of Control and Breakup
The flightcrew overstressed the airplane in an attempt to recover from the unusual attitude as the aircraft spiraled down. The Electra broke up, and falling wreckage damaged some houses; however, most of the wreckage fell in uninhabited, wooded areas.
Probable Cause
The official probable cause states: The aircraft's entry into an unusual attitude and the inability of the flight crew to analyze the flight condition before there was a complete loss of control. Although the precise reason for the loss of control was not identified, an undetermined failure of a component in the No.2 vertical gyro system, perhaps involving the amplifier and associated circuitry, probably contributed to the cause of the accident by incorrectly processing data to the co-pilot's approach horizon. The in-flight structural failure of the aircraft was due to overload.