Boeing 377 accident at London, England, 3 Jan 1951 (N-1036V)

Accident narrative

On January 3, 1951, a Pan American World Airways Boeing 377 Stratocruiser (N-1036V) was considerably damaged when its right main landing gear retracted during the landing roll at Heathrow Airport in London, England. The aircraft was operating a ferry flight with a crew of nine and no passengers. There were no injuries.

**The flight** The aircraft had arrived in the United Kingdom the previous day on a scheduled flight from the United States, but diverted to Hurn, England, because weather in London was below minimums. When London weather remained poor, the passengers were sent ahead by train. The aircraft was scheduled to ferry the 79 statute miles to London the following morning to operate a return flight to the United States.

The Stratocruiser departed Hurn at 0803. Captain A. L. McCullough (who had 1,269 hours on the aircraft type) and First Officer J. A. Livers (1,318 hours on type) were at the controls. The takeoff weight was below the maximum permissible, and the center of gravity was within limits. The flight plan noted that portions of the London runways were covered with three to four inches of snow and slush.

**The landing** First Officer Livers flew the aircraft from the right seat, while Captain McCullough occupied the left seat and handled some of the first officer's usual duties. The crew made a practice GCA approach to Runway 28. Knowing the runway conditions, they decided to use 30 degrees of flap for the landing to prevent snow and ice from being thrown against the flaps during the rollout.

The aircraft touched down at 0850. Captain McCullough described it as a "beautiful landing—very slightly nose up," with the main gear touching down at an indicated airspeed of about 110 knots and the nose wheel grounding almost immediately.

The captain reversed the number 2 and 3 propellers. Noting that the slush on the runway was getting deeper, he decided to raise the flaps. Instead of actuating the flap switch, he mistakenly moved the landing gear switch to the "up" position. Although he immediately returned it to "down," the landing gear warning horn sounded, and the right wing began to drop.

The aircraft settled onto its right wing and its number 3 and 4 engine nacelles. It skidded to a stop partly off the runway, turning approximately 110 degrees to the right. There was no violent deceleration.

**What the investigation found** The aircraft came to rest from the approach end of the 9,450-foot runway. Major damage was confined to the right wing tip, aileron, flap, and the propellers and nacelles of the right-side engines.

Because the runway was covered with slush from a previous snowfall, the exact touchdown point was difficult to determine. Ground witnesses estimated the touchdown occurred between 2,600 and 3,060 feet down the runway. The captain placed it at approximately 1,400 feet. Based on the available physical evidence, investigators placed the touchdown at 1,200 to 1,400 feet past the approach end. There was no evidence that the brakes were effectively applied at any time.

The Board noted that the landing gear operating switch is located on the control pedestal forward of the flap switch. It is protected against inadvertent movement by a hinged guard that must be raised before the switch toggle can be operated.

Investigators thoroughly examined and tested the right main landing gear and its control system, finding no mechanical or electrical failures. Each landing gear oleo strut is equipped with micro-switches. One safety system prevents the throttles from being moved into reverse thrust before the aircraft is grounded; this requires only one landing gear unit to be supporting weight. A separate system prevents an extended landing gear from retracting once it is firmly grounded, even if the cockpit switch is placed in the "up" position. However, if the cockpit switch is moved "up" during the landing roll, any gear unit will unlock and retract if it is not supporting enough weight to hold its micro-switch in the actuated position.

To rule out weather-related malfunctions, investigators removed the micro-switch from the right gear, filled its protecting rubber boot with water, and packed it in dry ice until frozen. The switch still functioned normally, successfully opening the circuit to prevent retraction.

Because exhaustive tests revealed no malfunctions, the Board concluded there was insufficient weight on the right landing gear to actuate the safety switch at the moment the gear control switch was moved to the "up" position.

**Probable cause** The Board determines that the probable cause of this accident was "the captain's action in mistakenly placing the landing gear control switch in the 'up' position during landing roll."