McDonnell Douglas DC-10-10 accident at US, 12 Jun 1972

Accident narrative

On June 12, 1972, an American Airlines McDonnell Douglas DC-10-10 experienced an in-flight separation of its aft bulk cargo compartment door at approximately 11,750 feet mean sea level near Windsor, Ontario, Canada. The separation caused a rapid decompression that collapsed the passenger cabin floor over the compartment, severing and jamming flight and engine control cables. The flightcrew maintained control and returned to Detroit Metropolitan Wayne County Airport for an emergency landing. There were 56 passengers and a crew of 11 aboard; two flight attendants and nine passengers received minor injuries.

**The flight**

American Airlines Flight 96 was a scheduled passenger flight from Los Angeles, California, to LaGuardia Airport, New York, with intermediate stops at Detroit, Michigan, and Buffalo, New York. The flightcrew consisted of Captain Bryce McCormick, who had 24,048 hours of flying time including 56 hours in the DC-10; First Officer Peter Whitney, with 7,947 hours and 75 in the DC-10; and Flight Engineer Clayton Burke, with 13,898 hours and 45 in the DC-10.

During the stop in Detroit, the ramp service agent servicing the aft bulk cargo compartment had difficulty closing the door. He closed the door electrically, listened for the motor to stop, and attempted to close the door handle. The handle is designed to close a small vent door, position lockpins behind the latches, and open the circuit to the cockpit warning lights. The agent could not close the handle with normal force, so he applied additional force with his knee. This caused the handle to stow, but the vent door was left in a slightly cocked position. A mechanic approved the release of the aircraft. According to the flight engineer, the cargo door warning light never illuminated during taxi-out or flight.

**The sequence of events**

Flight 96 took off from Detroit's Runway 03 Right at 1920, with the first officer flying. The flight was cleared to climb.

At about 1925, climbing at 260 knots indicated airspeed through approximately 11,750 feet, the flightcrew heard and felt a definite "thud." Dust and dirt flew into their faces, the rudder pedals moved to the full left-rudder position, all three thrust levers moved back to near flight idle, and the airplane yawed to the right. The captain momentarily lost his vision and thought they had suffered a midair collision.

The captain disengaged the autopilot and took control. Engines No. 1 and No. 3 responded to power application, but the No. 2 engine thrust lever could not be moved. Stabilized at 256 knots, aileron response was normal, but elevator response was extremely sluggish, and directional control required continuous left aileron. Rudder control was unavailable. The captain declared an emergency and was radar vectored back to Detroit.

In the cabin, the rapid decompression caused a fog to form. The decompression through the aft cargo door caused the cabin floor in the aft lounge area to fail downward and partially drop into the cargo compartment. Two flight attendants seated near the aft exits were thrown to the floor. The flight attendants prepared the passengers for a possible crash landing.

During the descent for an Instrument Landing System approach to Runway 03 Left, the captain stated that he secured the No. 2 engine because of limited elevator control, using power on the No. 1 and 3 engines to assist in pitchup control. He decided not to dump fuel due to unknown damage in the empennage. Extending the landing gear and 35° flaps at 150 knots increased the sink rate to 1,500 feet per minute. Additional thrust increased the airspeed to 160 to 165 knots and stabilized the sink rate at approximately 800 feet per minute. The airplane touched down at 1944 with an extremely flat deck angle.

Upon touchdown, the airplane veered right. The captain applied reverse thrust to engines No. 1 and 3 and full left aileron, while the first officer applied full reverse thrust to the left engine and brought the right engine out of reverse. This asymmetrical thrust provided directional control. The airplane paralleled the right side of the runway before beginning a gradual left turn, coming to rest 8,800 feet from the threshold. All occupants evacuated via the emergency slides. Some passenger injuries occurred at the bottom of the slides because the width of the double-occupancy surfaces made it difficult for evacuees to stabilize their sitting positions.

**What the investigation found**

The investigation found that the aft cargo compartment door had separated from the airplane, causing minor damage to the fuselage and substantial damage to the left horizontal stabilizer. The door was recovered several miles from the airport.

Examination of the door revealed that the four latches were nearly closed, but the lockpins were not engaged. The latches were approximately 0.1875 of an inch from their fully closed positions. The actuator support bracket was in place, but its two attach bolts had sheared. Tests of the door's electrical actuator showed that under load with low voltage, the unit crept slowly.

The system is designed to prevent the door handle from stowing if the lockpins are not in place. However, tests demonstrated that the handle could be stowed without the lockpins engaged if approximately 120 pounds of force was applied. This deflection of the mechanism permitted the pilot indicator switch to make contact, preventing the cockpit warning light from illuminating and leaving the crew with no warning that the door was improperly secured.

The Board concluded that the increasing pressure differential during the climb loaded the latches, failing the actuator support bracket fasteners. The latches sprang open, permitting the door to blow open.

Because the aft bulk cargo compartment was not equipped with pressure relief vents to the passenger cabin, the loss of the door caused the full differential pressure to be exerted on the cabin floor, failing its support structure. The floor collapsed into the cargo compartment, damaging the engine and flight control cables routed through the floor beams.

The left rudder cable was severed, permitting slack in the right rudder cable, which was deflected downward by the collapsed floor. This put a right signal into the rudder control system, causing the right yaw and the jammed left rudder pedal. Two elevator control cables were separated, and the downward loading on the intact cables required higher than normal control forces. The cables to the No. 2 engine thrust lever and shutoff valves were also separated; the Board believed the engine shut down when the cables separated, leaving no control of the engine from the cockpit.

The Board found no malfunctions in the hydraulic systems, wheel brakes, or nosewheel steering. While the manual stabilizer trim cables had failed and the position indicator was inoperative, the stabilizer trim switches on the control wheels functioned normally, though the crew was unaware of this and did not use trim for the approach.

**Probable cause**

The National Transportation Safety Board determined that the probable cause of this accident was "the improper engagement of the latching mechanism for the aft bulk cargo compartment door during the preparation of the airplane for flight. The design characteristics of the door latching mechanism permitted the door to be apparently closed, when, in fact, the latches were not fully engaged, and the latch lockpins were not in place."