Douglas DC-4 accident at Near El Paso, Texas, 8 Oct 1947 (NC-90432)

Accident narrative

At approximately 0755 on October 8, 1947, an American Airlines Douglas DC-4, registration NC-90432, executed a violent, uncommanded maneuver 35 miles west of El Paso, Texas. The aircraft pitched downward into part of an outside loop and became inverted before control was regained 300 to 400 feet above the ground. Of the 49 passengers and five crew members aboard, 30 passengers and all five crew members received minor injuries. The aircraft sustained minor damage and landed safely in El Paso.

### The flight

American Airlines Flight 311 originated in New York on October 7, bound for Los Angeles. During a scheduled stop in Dallas, Texas, a new crew took over. The crew consisted of three American Airlines captains: C. R. Sisto, Melvin Logan, and John Beck, along with stewardesses Marion Fagre and Barbara Chapman. Sisto, who had 10,400 flight hours, flew as pilot. Logan acted as copilot, and Beck rode as an observer to gain familiarization with the DC-4.

The flight departed Dallas at 0602. After reaching a cruising altitude of 8,000 feet, Captain Sisto, who was in command and flying from the left seat, exchanged seats with Captain Beck, moving to the jump seat located behind and between the two pilot seats.

### The maneuver

The flight proceeded uneventfully in clear weather and smooth air until shortly after passing El Paso. The aircraft began to climb without Captain Beck making any control inputs. To counter the climb, Beck rolled the elevator trim tab control forward, which would normally induce a nose-down attitude. When the airplane continued to climb, he continued rolling the trim control forward, which instead resulted in an increasing nose-high attitude.

Beck then attempted to return the trim tab to its former position. Before he could do so, the aircraft pitched downward violently, executing part of an outside loop and becoming inverted.

Captains Beck and Sisto, who did not have their seat belts fastened, were thrown to the top of the cockpit. In the process, they accidentally struck the feathering control, which feathered propellers numbers 1, 2, and 4. Captain Logan, whose seat belt was fastened, remained in his seat. Using power from the remaining number 3 engine, Logan managed to roll the aircraft out of its inverted position, regaining control approximately 300 to 400 feet above the ground. The feathered propellers were then unfeathered, and the crew flew the aircraft back to El Paso for a normal landing at 0811.

Passengers who did not have their safety belts fastened were thrown about the cabin, and the aircraft sustained damage to portions of the wing deicer boot and the interior cabin lining.

### What the investigation found

The Civil Aeronautics Board examined the aircraft and found no evidence of structural failure or mechanical malfunction.

In preliminary statements made the day after the accident, the crew indicated that the automatic pilot had been engaged just prior to the maneuver and might have malfunctioned. Investigators tested the automatic pilot, including in actual flight, and found it operated normally.

On October 15, the three pilots provided supplemental statements indicating that the automatic pilot had not been engaged at all. Instead, Captain Sisto stated that he had engaged the gust lock from the jump seat while the aircraft was in level flight. Captains Beck and Logan stated they were unaware of his action.

When the aircraft began to climb and the nose-down trim input failed to level the plane, Beck asked Sisto if the automatic pilot was on. Receiving a negative reply, Beck suspected the gust lock had become engaged and reached to neutralize the trim tab. However, before Beck could neutralize the trim, Sisto released the spring-loaded gust lock lever. This freed the elevator, which was immediately driven by the extreme nose-down trim setting, causing the violent downward pitch.

The Board noted that when Beck and Sisto were thrown to the ceiling and accidentally feathered three propellers, the resulting reduction in power decreased the speed of the dive and increased the aircraft's nose-heaviness. The Board observed that had the propellers not been feathered, the aircraft probably would have struck the ground. The Board commended Captain Logan for his prompt recognition of the situation and corrective action.

The investigation also found that Captain Sisto's medical certificate had expired more than six months prior to the accident. Following an action by the Administrator of Civil Aeronautics, the Board revoked Sisto's pilot certificate, finding he had demonstrated a disregard for safety and lacked necessary judgment.

### Probable cause

The Board determined that the probable cause of this accident was "the engaging and disengaging of the gust lock in flight, which was without the pilot's knowledge."