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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.<ref>{{cite web| url=http://www.nasa.gov/centers/dryden/history/pastprojects/Active/index.html| publisher=NASA| work=Past Research Projects| title=Active Home Page| access-date=2006-06-01| archive-date=September 30, 2006| archive-url=https://web.archive.org/web/20060930191203/http://www1.nasa.gov/centers/dryden/history/pastprojects/Active/index.html| url-status=dead}}</ref> 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 (engine, fan, propeller, pumps) caused damage to control systems. (Engine mounting failures are covered under structural failures, below.)
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*[[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.<ref>{{cite web|url=https://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20001214X43286 |title=DCA83AA029 |publisher=Ntsb.gov |date=1983-06-08 |access-date=2014-03-08}}</ref>
*[[LOT Polish Airlines Flight 5055]], an [[Ilyushin Il-62]]M, 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.
*[[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 E. Fitch|Dennis Fitch]], a [[Deadheading (aviation)|deadheading]] DC-10 instructor who had studied the case of [[Japan Airlines Flight 123|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.<ref>Gero 1997, p. 210.</ref>
*[[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.<ref>{{cite web|url=http://wikimapia.org/24202438/The-monument-on-the-site-of-the-crash-of-Flight-130 |title=The monument on the site of the crash of Flight 130 | memorial |publisher=Wikimapia.org |date=1994-01-03 |access-date=2014-03-08}}</ref>
====Controls damaged by structural failure====
In these incidents, a failure of structural components (bulkheads, doors, struts, mounts, spars, hull) subsequently damaged control systems.
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*[[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 [[List of accidents and disasters by death toll#Aviation|aviation death count]] ever.<ref>"Accident Details". ''[http://www.aaib.gov.uk/cms_resources.cfm?file=/8-1976%20TC-JAV.pdf Accident to Turkish Airlines DC-10 TC-JAV in the Ermenonville Forest on 3 March 1974 Final Report] {{webarchive|url=https://web.archive.org/web/20110602014551/http://www.aaib.gov.uk/cms_resources.cfm?file=/8-1976%20TC-JAV.pdf |date=2 June 2011 }}''. French State Secretariat for Transport. 1. Retrieved on 13 February 2011.</ref>
*[[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
*[[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 [[Leading-edge slat|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.<ref>Gero 1997, p. 189.</ref>
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*[[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.<ref>[http://www.bst.gc.ca/eng/rapports-reports/aviation/2005/a05f0047/a05f0047.pdf Flight 961 – Official accident report]. www.bst.gc.ca Retrieved: 1 June 2010</ref>
*[[National Airlines Flight 102]], a [[Boeing 747]] experienced a [[load shift]], damaging the [[aft pressure bulkhead]], severing the hydraulic lines that controlled the [[elevator (aeronautics)|elevators]]. This disabled the elevators, which were stuck in a pitch-up attitude. This caused the plane to [[stall (fluid dynamics)|stall]] and crash, killing all 7 occupants on board.
====Control system mechanical failures====
In these incidents, there was a failure of control system components themselves (e.g. cables, hydraulics, flaps, slats, ailerons, rudder, stabilizer, trim tabs, auto-pilot). (Control system fatigue failures are here, but improperly installed or incorrectly adjusted controls in the next section.)
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*[[Air Moorea Flight 1121]], a [[de Havilland Canada DHC-6 Twin Otter]], on 9 August 2007. Deterioration of the elevator cable from frequent takeoffs and landings, and likely jet-blast from larger aircraft, caused the cable to snap one minute after takeoff. The plane then nosedived and crashed into the ocean near [[Moorea-Temae Airport]] soon afterwards, killing all 19 passengers and the sole pilot.
====Control failures due to maintenance errors====
In these incidents, the failure of control system components was caused by improper installation or adjustment of control systems components by maintenance personnel.
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*[[Air Midwest Flight 5481]], a [[Beechcraft 1900D]], on 8 January 2003. On takeoff from [[Charlotte/Douglas International Airport]], the aircraft pitched up and stalled, despite the captain attempting to push the yoke for full elevator down. The aircraft smashed into a US Airways hangar 37 seconds later, killing all 21 passengers and crew aboard and injuring one person on the ground. The NTSB found out that the plane had been overweight and that during maintenance, the tension turnbuckles that governed elevator movement had been set incorrectly by an inexperienced mechanic. This caused the elevators to lose control authority upon takeoff.<ref>{{cite web|url=https://www.ntsb.gov/doclib/reports/2004/AAR0401.pdf |title=Loss of Pitch Control During Takeoff Air Midwest Flight 5481 Raytheon (Beechcraft) 1900D, N233YV Charlotte, North Carolina January 8, 2003 |date= |access-date=2014-03-08}}</ref>
====Controls damaged by explosive device/weapons====
*[[Philippine Airlines Flight 434]], a [[Boeing 747]], on 11 December 1994. The hydraulics were damaged by a bomb in the passenger cabin.<ref>[http://aviation-safety.net/database/record.php?id=19941210-0 Flight 934 – Aviation Safety Network] aviation-safety.net Retrieved: 1 June 2010.</ref>
*[[DHL shootdown incident in Baghdad|DHL Express Flight 209]], on 22 November 2003. The [[Airbus A300]] DHL aircraft, hit by a [[surface-to-air missile]], was the first jet airliner to land safely without any hydraulics using only engine controls.<ref>[http://aviation-safety.net/database/record.php?id=20031122-0 Aviation Safety Network] aviation-safety.net Retrieved: 1 June 2010.</ref>
*[[Azerbaijan Airlines Flight 8243]] on 25 December 2024. The [[Embraer E-Jet family|Embraer E190]] crashed during an attempted emergency landing near [[Aktau International Airport|Aktua International Airport]] in Kazakhstan killing 38 out of 67 onboard. The crash is a suspected shootdown event,<ref>{{Cite news |date=25 December 2024 |title=Growing evidence suggests Azerbaijan Airlines flight was targeted by missile strike |url=https://www.turkiyetoday.com/world/growing-evidence-suggests-azerbaijan-airlines-flight-was-targeted-by-missile-strike-97513/ |access-date=25 December 2024 |work=Türkiye Today }}</ref> with the aircraft entering a [[phugoid]] cycle.{{cn|date=December 2024}}
==== Controls damaged by pilot error ====
In these incidents, pilot error resulted in control system damage.
*[[Pan Am Flight 845]], a [[Boeing 747]], on 30 July 1971. When taking off from [[San Francisco International Airport]], the plane struck the [[approach lighting system]] after taxiing onto a much too short runway. After the impact, the plane continued into the takeoff roll, though its fuselage, landing gear, and 3 out of 4 hydraulic systems were badly damaged. After making a full circle over the Pacific Ocean for an hour and 42 minutes and dumping fuel, the plane made a hard emergency landing at San Francisco, ending on its tail. All 218 passengers survived with a few minor injuries.<ref>[[National Transportation Safety Board]] (24 May 1972), {{usurped|[https://wayback.archive-it.org/all/20070621014610/http://www.airdisaster.com/reports/ntsb/AAR72-17.pdf Aircraft Accident Report]}}, retrieved 27 March 2014</ref>
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*[[American Airlines Flight 587]], [[Airbus A300]], November 12, 2001. A pilot's excessive rudder inputs caused the vertical stabilizer to fracture and separate from the aircraft. See complete entry in [[#Controls damaged by structural failure|structural failures]] above.
====Controls damaged by mid-air collision====
These incidents describe mid-air collisions that mainly damaged control systems of at least one of the aircraft, which may or may not have been recoverable.
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==
====Controls damaged by structural failure====
* On 4 April 1975, A [[1975 Tân Sơn Nhứt C-5 accident|Lockheed C-5 Galaxy]] (registered as {{not a typo|68-0218}}) making the first flight of [[Operation Babylift]], had the failure of the rear loading ramp, causing the cargo door to open explosively. This caused an [[explosive decompression]], and in turn, severed control cables to the tail, causing two of four hydraulic systems to fail, including those for the rudder and elevator, and leaving the flight control with only the use of one [[aileron]], [[Spoiler (aeronautics)|spoilers]], and power. The crew had to wrestle at the controls by adjusting the power setting and using the remaining one aileron and spoilers in order to return to [[Tan Son Nhut Air Base]], but ended up crash landing in a [[Paddy field|rice paddy]], killing 138{{efn|The number of fatalities vary depending on the source, but official accounts state 138 of 314 on board were killed.}} of the 314 people on board.<ref>{{Cite journal |date=1978 |title=Last Flight From Saigon |url=https://books.google.com/books?id=TmSApdkHyWIC |journal=USAF Southeast Asia Monograph Series |publisher=Diane Publishing |volume=IV |pages=29 |isbn=1-4289-8211-6}}</ref><ref>{{Cite web |last=Ranter |first=Harro |title=ASN Aircraft accident Lockheed C-5A Galaxy 68-0218 Saigon-Tan Son Nhat International Airport (SGN) |url=https://aviation-safety.net/database/record.php?id=19750404-0 |access-date=2022-08-19 |website=aviation-safety.net}}</ref>
====Controls damaged by explosive device/weapons====
In the [[Charlie Brown and Franz Stigler incident]] on 20 December 1943, a Boeing B-17F Flying Fortress of the 527th Bombardment Squadron was tasked with carrying out a bomb run on [[Bremen]], [[Germany]], in formation with other B-17Fs. Before the bomber released its bomb load, accurate [[Anti-aircraft warfare|flak]] shattered the Plexiglas nose, knocked out the #2 engine and further damaged the #4 engine, which was already in questionable condition and had to be throttled back to prevent [[overspeed]]ing. This caused the plane to fall back from the formation and left it vulnerable to enemy attack. The B-17F was then attacked by over a dozen enemy fighters (a combination of [[Messerschmitt Bf 109]]s and [[Focke-Wulf Fw 190]]s) of [[Jagdgeschwader 11|JG 11]] for more than ten minutes, causing the pilot to lose consciousness and putting the B-17F into a steep dive. The pilot later regained consciousness and recovered the plane from the dive. Further damage was sustained from the attack, including to the #3 engine, reducing it to only half power (meaning the aircraft had effectively, at best, 40% of its total rated power available). The bomber's internal oxygen, hydraulic, and electrical systems were also damaged, and the bomber had lost half of its rudder and port elevator, as well as its nose cone. The crew on board were also wounded with one of them being killed. After being escorted by a [[Luftwaffe]] Messerschmitt Bf 109 G-6 to be out of German airspace, the B-17F landed at [[RAF Seething]].<ref>{{Cite web |title=Chivalry in the Air – Chivalry Today |url=https://chivalrytoday.com/chivalry-air/ |access-date=2022-08-20 |language=en-US}}</ref>{{sfn|Makos|Alexander|2012|pp=181, 184–85}}<ref>{{Cite web |author=John Blake |title=Two enemies discover a 'higher call' in battle |url=https://www.cnn.com/2013/03/09/living/higher-call-military-chivalry/index.html |access-date=2022-08-20 |website=CNN}}</ref><ref>{{Cite web |last=tara |date=2020-12-21 |title=This Day in History: The Charlie Brown & Franz Stigler incident |url=https://www.taraross.com/post/tdih-brown-stigler-incident |access-date=2022-08-20 |website=Taraross |language=en}}</ref>
====Controls damaged by mid-air collision====
[[File:19430201AllAmericanB17inFlight.jpg|alt=
*On 1 February 1943, the ''[[All American (aircraft)|All American]]'' [[Boeing B-17 Flying Fortress|B-17F]] was in formation with other bombers of the [[414th Expeditionary Reconnaissance Squadron|414th Bombardment Squadron]] to return to their base near [[Biskra]], [[Algeria]] when two [[Messerschmitt Bf 109]]s attacked the lead bomber and the ''All American.'' The first Bf 109 was downed by the bombers but the second continued its attack, flying towards the ''All American'' until its pilot was shot dead by machine gun fire and the Bf 109 collided with the ''All American'', shearing off the bomber's left [[horizontal stabilizer]] and leaving a huge hole at the tail section. The only thing holding the B-17F together was the metal frame connecting the tail section and the rear gunner.<ref>{{Cite web |date=2016-08-07 |title=Commentary - A new perspective on a challenging day at work |url=http://www.charleston.af.mil/news/story.asp?id=123438088 |archive-url=https://web.archive.org/web/20160807134932/http://www.charleston.af.mil/news/story.asp?id=123438088 |archive-date=2016-08-07 |access-date=2022-09-01 }}</ref><ref name="Leone">{{Cite web |last=Leone |first=Dario |date=2017-11-09 |title=THE STORY OF "ALL AMERICAN", THE B-17 THAT MADE IT HOME AFTER HAVING BEEN SLICED BY THE WING OF AN Me 109 |url=https://theaviationgeekclub.com/story-american-b-17-made-home-sliced-wing-109/ |access-date=2022-09-01 |website=The Aviation Geek Club |language=en-GB}}</ref><ref>{{Cite web |last=WarbirdsNews |date=2013-06-27 |title=WWII's B-17 "All American" Separating Fact and Fiction |url=https://warbirdsnews.com/warbird-articles/wwiis-b-17-all-american-separating-fact-fiction.html |access-date=2022-09-01 |website=Vintage Aviation News |language=en-US}}</ref> This caused the rudder, electricals, and oxygen systems to be damaged, removing the tail wheel and leaving only one operating elevator cable when the other control cables were destroyed.<ref>{{Citation |title=B17 All American ~ (Rev. 2a) (720p HD) |url=https://www.youtube.com/watch?v=_OAPgo1iUvM |language=en |access-date=2022-09-01}}</ref> Despite the mid-air collision, none of the crew on board were injured and the B-17F remained airborne. The other bombers slowed down to maintain formation with the ''All American'' to protect it from potential attacks from other [[Messerschmitt Bf 109]]s, which never happened. The B-17F managed to land back at the base with the tail section dragging the landing strip.<ref name="Leone"/>
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==
====Extreme cold====
[[File:XCO-5 and Lt Macready.JPG|thumb|left|alt=A monochrome photograph of a biplane parked on an airfield, with a man posed leaning against its fuselage with his hands in his pockets|The [[Engineering Division TP-1|XCO-5]], an experimental observation biplane flown in altitude tests]]
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====Maintenance or pilot error====
*The aircraft designer [[Roy Chadwick]] was killed on 23 August 1947 during a crash on take-off of the prototype [[Avro Tudor|Avro Tudor 2]], ''G-AGSU'', from Woodford airfield. The accident was due to an error in an overnight servicing in which the [[aileron]] control cables were inadvertently crossed.
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[[File:MD-11 shortly after touchdown.jpg|thumb|The MD-11 Propulsion Controlled Aircraft (PCA) lands for the first time under engine power only on Aug. 29, 1995, at NASA's Dryden Flight Research Center in California]]
NASA personnel at [[Dryden Flight Research Center]] worked on the design of an aircraft control system using only thrust from its engines. The system was first tested on a [[McDonnell Douglas F-15 Eagle]] in 1993, piloted by [[Gordon Fullerton]].<ref name="MD-11 PCA">{{cite web|url=https://www.nasa.gov/centers/dryden/multimedia/imagegallery/MD-11PCA/MD-11PCA_proj_desc.html |title=MD-11 Propulsion Controlled Aircraft (PCA)|publisher=www.nasa.gov |date= |access-date=2021-05-16}}</ref> The system was then applied to a [[McDonnell Douglas MD-11]] airliner, and Fullerton made its first propulsion-controlled landing in August 1995.<ref name ="MD-11 PCA"/> Later flights were made with the center engine at idle speed so the system could be tested using the two wing-mounted engines, simulating the more common airliner layout.<ref>Tucker, p. 29.</ref>
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==Notes==
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