Delta Air Lines Flight 1080 was a scheduled flight from San Diego, California, to Atlanta, Georgia, notable for the incident that occurred on April 12, 1977, during the San Diego to Los Angeles leg of the flight.[3] Unbeknownst to the crew, the Lockheed L-1011's left elevator had become stuck in a fully upwards position. This led to the aircraft pitching up aggressively and causing the aircraft to lose speed and nearly stall.[4] The pitching force, unable to be overcome by fully pushing the control column down, was counteracted by reducing the thrust on the L-1011's wing engines but not the tail engine. The differential thrust, along with moving all the passengers as far forwards as possible in the cabin, pitched down the nose of the airliner and allowed the pilots to land the aircraft.[1][5] The entire incident lasted 55 minutes.[2]
The aircraft was a two-year-old Lockheed L-1011-385-1 TriStar registered as N707DA. It was delivered to Delta Air Lines on 24 May 1974. At the time of the accident, the aircraft had registered 5,000 flight hours.[citation needed]
Crew
In command was 56-year-old Captain Jack McMahan, who had 23,000 flight hours, of which 2,000 were in the L-1011. The first officer, 34-year-old Wilbur Radford, had 10,000 flight hours, 1,500 were on the L-1011, and 30-year-old Flight Engineer Steven Heidt having 500 out of his 5,000 total flight hours on the L-1011. There were eight flight attendants on board the aircraft.[1][6]
Incident timeline
Takeoff
At 23:53 PDT (19:53 UTC), the conditions were reported as 800 ft of overcast, visibility 5 miles (8km), temperature 58°F (14°C), winds 260° at 8mph (13km/h). While taxing to runway 27, the crew performed a flight control check, and during this check the left stabilizer jammed upwards. As the aircraft rolled down the runway, the takeoff was described as "normal" until Vr speed 126kn (233km/h; 145mph) the nose rotated off the ground with little to no pull on the control column.[2][6][1]
Initial problems
The aircraft involved in the incident, still flying almost twenty years later (in 1996), by then being operated by American Trans Air (ATA)
When the aircraft suddenly pitched up, it was found to be slightly controllable, although McMahan did push the column fully forward with little response. The captain then checked the stabilizer trim setting; it was set at the correct 3.5° nose up. The aircraft seemed to stop pitching up at 15°, the gear was retracted and the plane seemed to return to a normal flight condition. At 400ft (120m), the aircraft began pitching up again, from 15° to 18°. The crew kept trying to use the thumbwheel trim after the movement of the thumbwheel stopped. The controls were described as very sluggish, with little response. The back-up system, which overrides the electric trim, was used, but it didn't result in a change in control. The SPI instrument indicated that the stabilizer was already 'zeroed out', and so the pilots were still puzzled as to why the aircraft kept pitching upwards. Heidt, at the request of McMahan, looked over and checked the hydraulic systems, as McMahan believed that one of the hydraulic systems had failed. While Radford conducted an area test, McMahan unlatched and latched any switches associated with trim, and Heidt double checked the hydraulics and checked for any popped circuit breakers. By the time the aircraft reached 3,000ft (900m), all procedures for jammed controls, trim, axis jam, and hydraulic malfunctions had been performed with no change in control. The crew informed San Diego Departure Control that they were experiencing a pitch issue, and instead of switching frequencies, they requested to stay with departure control. They were later handed off to a coast controller after enough controllability was regained.[2]
Near stall
The aircraft then began a pitch up maneuver, unable to be counteracted by both the first officer and the captain, climbing at about 5,000ft/min (25m/s), with the airspeed decaying to below V2 speed. While the crew were desperately trying to push the nose down, flight attendants were gathering all the passengers and sending them to sit as far forward as possible.[2]:184 The captain, perhaps thinking in a last ditch effort to regain control, fully reduced thrust on the number one and three engines, and maintained full power on the number two (central tail) engine. This worked in getting the nose down and established enough controllability that the crew now made an attempt back towards the airport.[2]
Returning to the airport
With some controllability established, the crew made a turn towards the airport. The crew, after lining up with the runway, attempted an instrument approach. This approach was successful in getting the aircraft on the ground. Reverse thrust was used on all the engines, heavily on engines 1 & 3, with low power on engine 2. The crew taxied the aircraft back to the gate and passengers were disembarked and re-booked onto another flight.[2]
Investigation
The investigation found that the pressurization and depressurization of the L-1011 during multiple flight cycles had caused water to be pushed inside the left elevator aft drive quadrant (also referred to as the bell crank), heavily corroding it and causing it to become jammed during a routine control surfaces check prior to takeoff. The FAA issued an emergency airworthiness directive instructing airlines to do a check of the bearing. This verification, however, was not sufficient to prevent takeoff with a jammed elevator; and a similar incident followed two months later. The FAA then made it mandatory for crews to inspect the elevators before each takeoff.[1][7]
Aftermath
As a result of the incident, Lockheed redesigned the elevator systems to be redundant upon failure of the bearings, as well as adding a seal to the bearing and a deflector to reduce the amount of water contacting the part.[1] Lockheed also modified the pilot's manual to improve the Pitch Axis Control Assist Procedures. The FAA further made it mandatory for pilots to be informed of these changes.[7][8]
For his skill in landing the crippled aircraft, the captain, Jack McMahan, was awarded the FAA's Distinguished Service Award.[2]
See also
Alaska Airlines Flight 261, a MD-82 that suffered a failure of the jackscrew in the stabilizer, leading to the deaths of 88 people.
↑ Montoya, Howell, Bundick, Ostroff, Hueschen, Belcastro, R. J., W. E., W. T., A. J., R. M., Christine (August 1983). "Restructurable Controls"(PDF). 19830025625.pdf. Retrieved November 16, 2024.{{cite web}}: CS1 maint: multiple names: authors list (link)
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