Boeing 707 accident at Atlantic Between London, England and Gander, Newfoundland, 3 Feb 1959 (N-712PA)

Accident narrative

On February 3, 1959, at 2205 G.m.t., Pan American World Airways Flight 115, a Boeing 707 (N 712PA), made an uncontrolled descent of approximately 29,000 feet over the Atlantic Ocean between London, England, and Gander, Newfoundland. The aircraft was recovered at an altitude of approximately 6,000 feet and flown to Gander for a safe landing. A few of the 119 passengers and 10 crew members sustained minor injuries, and the aircraft suffered extensive structural damage.

**The flight**

Flight 115 was a scheduled service from Paris, France, to New York, New York, with intermediate stops planned at London and Gander. The flight crew included Captain Waldo Lynch, who had 11,185 flying hours with 350 in the Boeing 707, and Copilot Samuel Peters, who had 14,952 hours with 269 in the 707. Both were supervisory personnel qualified as pilots in command. A flight engineer, a navigator, six cabin crew, and a company dispatcher were also aboard.

The flight departed London at 1845 G.m.t. on an IFR flight plan to Gander. Near 30 degrees west longitude, the aircraft encountered a frontal condition with heavy thunderstorms, moderate turbulence, and light icing. The crew obtained clearance to climb from 29,000 to 35,000 feet. At this altitude, the aircraft was on top of the weather in smooth air with all stars visible.

**The descent**

At approximately 2150, Captain Lynch left the cockpit and went to the main cabin. Copilot Peters remained in the right seat. The aircraft was cruising at Mach 0.82 with the autopilot engaged in the manual mode and the altitude hold on.

At 2200, the navigator posted a heading change requiring a left turn of about 20 degrees. Peters used the autopilot turn knob to comply, observed the new heading on his radio magnetic indicator, and noted the autopilot was holding the heading normally. He then began working on a "How Goes It" curve on a clipboard in his lap, computing time, distance, and fuel. With his headset on both ears waiting to copy a weather broadcast, he stated he did not observe the forward instrument panel during this time.

Peters's first indication of abnormality was airframe buffet, immediately followed by rapidly building positive acceleration forces. The buffeting increased, and his instrument panel lights went out. He looked at the captain's lighted panel and saw the artificial horizon had tumbled. Glancing up, he saw the stars moving rapidly counterclockwise, indicating the aircraft was in a nosedown right spiral about to roll inverted. He grabbed the control wheel, pushed the autopilot release button, and attempted to apply left aileron and rudder, but was virtually immobilized by the G-forces. Warning lights flashed and the Mach warning bell sounded.

Captain Lynch returned to the cockpit with considerable difficulty. The flight engineer reminded him the power was still at cruise thrust, and Lynch pulled the power levers to idle. He pulled himself into his seat, which had been moved fully rearward. The G-forces made it difficult or impossible for the crew to move their heads, hands, or feet. Lynch noted the altimeter passing through 17,000 feet turning at a terrific rate, and the turn and bank indicator full to the right. Seeing the copilot struggling, Lynch shouted, "I have command."

The stabilizer was in the full nosedown position, and Lynch's electric trim button failed to function. The navigator managed to fasten the captain's safety belt. Lynch rolled the wings level, relieving the G-forces. The flight engineer pulled the circuit breaker to deactivate the stabilizer system and began manually rolling both stabilizer wheels toward the up position.

Passing through 8,000 feet, Lynch pulled the yoke back with a steady pull. At 6,000 feet, after a couple of seconds of violent buffeting, the aircraft ceased descending and began a steep climb. By 9,000 feet, the wings were level. Lynch noticed the stabilizer cutout switch was in the "on" position and the Mach trim switch was "off". The crew advised Gander of the difficulty, obtained a cruise altitude of 31,000 feet, and manually flew the aircraft to Gander without further incident.

**What the investigation found**

Inspection at Gander revealed extensive structural damage. The lower surface skin of both horizontal stabilizers, the center section web, and both wing panels were buckled. A three-foot section of the right wing-to-fuselage fairing had separated in flight. Engine nacelle struts were buckled, and shear bolts had partially failed.

The flight engineer reported seeing the stabilizer pitch trim move toward a nosedown position early in the descent, and Captain Lynch found it full nosedown upon his return. Copilot Peters testified he did not touch the electric stabilizer trim switch on his control wheel.

Tests of the PB-20D autopilot system revealed minor discrepancies. The comparator unit, which monitors for errors and automatically disengages the system, required a five-degree pitchup change for disengagement rather than the specified four degrees. An amplifier-computer relay serving the warning light circuit was misaligned as if it had been dropped. The vertical gyro transmitter's rate gyro motor had an open winding, and the pitch trim potentiometer failed to recenter after disengagement.

The Board analyzed these irregularities as minor and unable to have caused the disengagement. The Board noted that nuisance disengagements can occur from transitory spurious signals, or from accidental operation of the trim switch, disconnect button, or engage switch by the copilot. Because the autopilot disengage warning light is a flashing red light, it should have been observed in the dark cockpit unless it failed or was shielded. The dimming cap was found in the full down position at Gander, which the Board believed probably shielded the light.

The Mach trim system, designed to counteract a nosedown tendency at high speeds, was tested and found capable of normal operation. The Board concluded it had not been turned on by the crew, as it would have provided noseup trim as the Mach number increased. A test of the Mach warning system indicated the bell's center bolt was loose, producing a buzzing sound rather than a clear ring.

The Board stated that the change in stabilizer trim to full nosedown could have resulted from inadvertent pressure on the electric switch by the copilot; despite his testimony to the contrary, the Board considered this the only logical explanation.

The aircraft's flight recorder tape was exhausted at the time of the accident. Investigation showed a company mechanic had installed a 51-foot tape instead of the usual 100-foot length. Slippage of the masking tape retaining the foil to the spool caused intermittent record advance. Microscopic examination of this abnormal record verified the abrupt descent from 35,000 to 6,000–8,000 feet and indicated the aircraft reached a speed equivalent to Mach 0.95. The Board noted the company was lax in its inspection of the recorder.

The Board concluded the autopilot disengaged for reasons unknown, and the aircraft entered the steep spiral gradually. It noted it does not condone extended absences from the cockpit and believes the remaining pilot should devote his entire attention to flying the aircraft.

**Probable cause**

The Board determines that the probable cause of this accident was the inattention of the copilot to the progress of the flight, during the absence of the captain from the cockpit, following the involuntary disengagement of the autopilot. Contributing factors were the autopilot disengage warning light in the dim position and the Mach trim switch in the "off" position.