Flight with disabled controls


Throughout a normal flight, a pilot controls an aircraft through the use of flight controls including maintaining straight and level flight, as well as turns, climbing, and descending. Some controls, such as a "yoke" or "stick" move and adjust the control surfaces which affects the aircraft's attitude in the three axes of pitch, roll, and yaw. Other controls include those for adjusting wing characteristics and those that control the power or thrust of the propulsion systems. The loss of primary control systems in any phase of flight is an emergency. Aircraft are not designed to be flown under such circumstances; however, some pilots faced with such an emergency have had limited success flying and landing aircraft with disabled controls.
Control system failures resulting in disabled controls have resulted in a number of aviation incidents and accidents. Some incidents occurred where controls were not functioning correctly prior to take-off, others where the failure developed during flight. A loss of control can occur when an unrelated failure, such as an engine failure, causes damage to control related systems. For instances, in several incidents an engine broke apart, causing the failure of main and redundant hydraulic systems, which disabled all control surfaces. Some or all controls can become inoperative from extreme weather conditions, due to collisions, due to poor maintenance or mistakes made by maintenance workers, as a result of pilot error, due to failures of the flight control system, or due to design or manufacturing flaws.

Control techniques

Normal flight

In normal flight, maneuvering an aircraft requires some combination of controls, which are often interactive in their effect.
  • For instance, to climb to a higher altitude, the pilot can increase thrust which will cause the aircraft to climb while maintaining airspeed.
  • * Alternately, the pilot may climb by pitching the aircraft up, though in this case airspeed decreases.
  • Normally to make a turn, the pilot banks left or right by adjusting the ailerons on the wings to increase lift on one wing, and decrease lift on the other. The asymmetric lift causes asymmetric drag, which causes the aircraft to yaw adversely. To correct the yaw, the pilot uses the rudder to perform a coordinated turn.
  • * In a multi-engined aircraft, the loss of thrust in one engine can also cause adverse yaw, and here again the rudder is used to regain coordinated flight.

    Flight with disabled controls

A basic means of controlling an aircraft with disabled flight controls is making use of the position of the engines. If the engines are mounted under the centre of gravity, as in underwing passenger jets, then increasing the thrust will raise the nose while decreasing the thrust will lower it. This control method may call for control inputs that go against the pilot's instinct: when the aircraft is in a dive, adding thrust will raise the nose and vice versa.
Additionally, asymmetrical thrust has been used for directional control: if the left engine is idled and power is increased on the right side this will result in a yaw to the left, and vice versa. If throttle settings allow the throttles to be shifted without affecting the total amount of power, then yaw control can be combined with pitch control. If the aircraft is yawing, then the wing on the outside of this yaw movement will go faster than the inner wing. This creates higher lift on the faster wing, resulting in a rolling movement, which helps to make a turn.
Controlling airspeed has been shown to be very difficult with engine control only, often resulting in a fast landing. A faster than normal landing also results when the flaps cannot be extended due to loss of hydraulics.
Another challenge for pilots who are forced to fly an aircraft without functioning control surfaces is to avoid the phugoid instability mode, which requires careful use of the throttle.
Because this type of aircraft control is difficult for humans to achieve, researchers have attempted to integrate this control ability into the computers of fly-by-wire aircraft. Early attempts to add the ability to real aircraft were not very successful, the software having been based on experiments conducted in flight simulators where jet engines are usually modelled as "perfect" devices with exactly the same thrust on each engine, a linear relationship between throttle setting and thrust, and instantaneous response to input. More modern computer systems have been updated to account for these factors, and aircraft have been successfully flown with this software installed. However, it remains a rarity on commercial aircraft.

Accidents and incidents

Commercial aircraft

Incidents where disabled, damaged, and/or failed control systems were a significant or primary cause of the accident.

Controls damaged by engine failure

In these incidents, a failure of propulsion systems caused damage to control systems.
  • Eastern Air Lines Flight 935, a Lockheed L-1011 TriStar, on September 22, 1981. Suffered an uncontained failure of the No. 2 engine on takeoff from Newark, New Jersey. The crew were able to land the aircraft safely at John F. Kennedy International Airport with some limited use of the outboard spoilers, the inboard ailerons and the horizontal stabilizer, plus the differential engine power of the remaining two engines.
  • Reeve Aleutian Airways Flight 8, a Lockheed L-188 Electra, on 8 June 1983. Flying over Cold Bay, Alaska, the plane's number 4 engine propeller detached itself from the engine and cut a hole in the plane as it flew underneath it. The resultant damage inflicted by the propeller caused an explosive decompression, severed cables connected to the plane's throttles and control surfaces and left the flight deck crew of three with only autopilot that had no lateral control. After managing to wrench the ailerons and elevators into minimal working condition, the crew tried to land at Anchorage at high speed. They had to make a go-around, but landed on the second attempt, saving all 10 passengers on board.
  • LOT Polish Airlines Flight 5055, an Ilyushin Il-62M, on 9 May 1987. According to the Polish investigatory commission, the cause of the crash was the disintegration of an engine shaft due to faulty bearings inside engine No. 2, which seized, causing extensive heat. This in turn caused the consequent damage to engine No. 1, rapid decompression of the fuselage, and a fire in the cargo hold, as well as the loss of elevator controls and progressive electrical failures. The crew decided to return to Warsaw Okecie Airport using only trim tabs to control the flight of the aircraft. They lost their struggle to land about 5 km from the runway in the Kabacki Forest. All 172 passengers and 11 crew members perished.
  • United Airlines Flight 232, a McDonnell Douglas DC-10, on 19 July 1989. A fan disk in the No. 2 engine fractured, severing most of the flight controls. Dennis Fitch, a deadheading DC-10 instructor who had studied the case of JAL Flight 123, was able to help the pilots steer the aircraft using throttle differential. Despite the break-up of the aircraft on landing, 175 of 285 passengers and 10 of the 11 crew members survived.
  • Baikal Airlines Flight 130, a Tupolev Tu-154, on 3 January 1994. When starting the engines before takeoff, the pilots noticed a warning light signaling dangerous rotation of the starter in engine #2. Believing the warning to be false, they decided to take off anyway. During the initial climb, the starter failed and a fire broke out in the #2 engine. The fire damaged all three hydraulic lines, rendering the plane uncontrollable. After 12 minutes of the crew trying to control the sliding trajectory of the plane, it eventually crashed into a dairy farm near Mamony town at 500 km/h, killing all 124 people aboard and one man on the ground.

    Controls damaged by structural failure

In these incidents, a failure of structural components subsequently damaged control systems.
  • American Airlines Flight 96, a McDonnell Douglas DC-10, on 12 June 1972. The failure of the rear cargo door caused an explosive decompression, which in turn caused the rear main cabin floor to collapse and severed flight controls. The pilots had only limited ailerons and elevators; the rudder was jammed. The number two engine also ran down to idle at the time of decompression. The aircraft landed safely at Detroit-Metropolitan Airport.
  • Turkish Airlines Flight 981, a McDonnell Douglas DC-10, on 3 March 1974. Similar to American Airlines Flight 96, the flight experienced an explosive decompression, when flying over the town of Meaux, France, caused by a rear cargo door failure. The rear main cabin floor collapsed and severed all flight controls. While the plane went into a vertical dive, the captain called for "Speed!", meaning increasing engine thrust to push the plane's nose up. The plane began to level out, but had lost too much altitude and slammed into the Ermenonville Forest. All 346 people on board were killed upon impact, and it became the worst single aircraft disaster without survivors, and the fourth deadliest aviation death count ever.
  • Delta Air Lines Flight 1080, a Lockheed L-1011 Tristar, on April 12, 1977, suffered a structural failure of a bearing assembly controlling the aircraft's left stabilizer, which caused it to jam in a full trailing edge up configuration. The plane pitched abruptly upwards and the pilots could not counteract the pitching force even when pushing the control column fully forward. This caused the plane to lose speed and nearly stall. The pilot managed to regain control by using the Tristar's tail engine at maximum power and lowering the thrust on the wing engines in order to generate differential thrust, together with the cabin crew moving the passengers forward to alter the center of gravity. The airliner landed at Los Angeles International Airport, with all 41 passengers and 11 crew being unharmed.
  • American Airlines Flight 191, a McDonnell Douglas DC-10, on 25 May 1979. The failure of the #1 engine mounting pylon and subsequent separation of the engine from the aircraft resulted in severed hydraulic lines and electrical system damage. The left wing slats retracted due to the loss of hydraulic pressure and aerodynamic forces, while the right wing slats remained extended. The damaged electrical system prevented the slat retract indicators and stick-shaker on the yoke from functioning, so the crew was not alerted to the slat retraction nor impending stall. All 271 on board were killed, as well as two on the ground at O'Hare International Airport in Chicago, Illinois, making it the deadliest aviation accident in U.S. history.
  • Japan Air Lines Flight 123, a Boeing 747, on 12 August 1985. A faulty repair years earlier had weakened the aircraft's rear pressure bulkhead, which failed in flight. The vertical stabilizer and much of the aircraft's empennage was blown off during the decompression. The decompression also ruptured all four hydraulic lines which controlled the aircraft's mechanical flight controls. The pilots were able to continue flying the aircraft with very limited control, but after 32 minutes the aircraft crashed into a mountain, killing 520 of the 524 people aboard in the deadliest single aircraft disaster in history.
  • American Airlines Flight 587, Airbus A300, November 12, 2001. This was the second-deadliest aviation accident in U.S. history, with 251 passengers and 9 crew members killed, as well as five people on the ground. According to the NTSB, the aggressive use of the rudder controls by the first officer stressed the composite vertical stabilizer until it separated from the aircraft. The complete loss of the vertical stabilizer meant the loss of all rudder control. As the pilots struggled to control the aircraft, it entered a flat spin. The resultant forces caused the engines to separate from the aircraft, and it slammed into the ground 14 seconds later.
  • Air Transat Flight 961, an Airbus A310, on 6 March 2005, catastrophic structural failure: the rudder detached from the aircraft with a loud bang and the aircraft began a dutch roll. The pilots regained enough lateral control, albeit with difficulty, to land the aircraft safely at Varadero-Juan Gualberto Gomez Airport.
  • National Airlines Flight 102, a Boeing 747 experienced a load shift, damaging the aft pressure bulkhead, severing the hydraulic lines that controlled the elevators. This disabled the elevators, which were stuck in a pitch-up attitude. This caused the plane to stall and crash, killing all 7 occupants on board.