Pan Am Flight 115, operated by Pan American World Airways Boeing 707-121 N712PA (Clipper Washington), was a commercial flight from Paris via London to New York City. At 22.05 GMT (16.05EDT) on 3 February 1959 it was involved in one of the most notable jet upset incidents of the jet airliner age, over the North Atlantic near Newfoundland.
Pan Am Flight 115 Wikipedia
The jet, crewed by pilot-in-command Captain Waldo Lynch, Captain Samuel Peters, flight engineer George Sinski, and navigator John Laird, with 119 people on board, experienced an emergency descent of 29,000 feet from 35,000 feet, but the crew managed to recover at approximately 6,000 feet. The crew made an emergency landing at Gander with damaged flaps.
Evidence was subsequently given to the then United States Civil Aeronautics Board that the aircraft was flying at 35,000 ft at Mach 0.82 and at a weight of about 195,000 lb. During the previous two flights the Bendix PB-20 autopilot was reported in one case to have caused a nose-down pitch and in another to have disconnected following a change of heading of 20 deg, but on February 3 operation was found to be normal on arrival at Gander. The disengagement warning light was fully dimmed.
Flight Magazine's issue of 3 April 1959 reported "Captain Waldo Lynch, the pilot-in-command, said that the aircraft went into a sharp manoeuvre downward and to the right. At 17,000ft the airspeed was over 400 kt, the electric trim button was inoperative, and his gyro horizon had tumbled. The co-pilot, recounted that "At 2200Z the navigator posted a change in heading requiring left turn. Used autopilot turn knob. Turn O.K. . . . Then light buffeting, plus positive load factor building up. . . . Heavy buffeting caused panel lights to fail."
The flight engineer said that he was pinned to his seat as the Mach warning sounded. When the g load was relieved, he pulled the tailplane-power and autopilot circuit-breakers because he thought that the tailplane had "run away." Full nosedown tailplane inclination of 3 degrees was indicated. He wound it back to the nose-up position but later trimmed nose-down.
Aviation Safety Network reports the cause of the incident as unintentional disconnection of autopilot while captain had left the cockpit and entered the passenger cabin. The Copilot didn’t pay sufficient attention to the instruments and the plane went into a dive in a clockwise spiraling turn.
After being operated by a number of firms, the airframe was finally scrapped in August 1984, at Taipei, Taiwan.