American Airlines Flight 191 was a regularly scheduled passenger flight operated by American Airlines from Chicago's O'Hare International Airport to Los Angeles International Airport. On May 25, 1979, the McDonnell Douglas DC-10-10 operating this flight crashed just moments after takeoff from Chicago. All 258 passengers and 13 crew on board were killed, along with two people on the ground. With 273 fatalities, it is the deadliest aviation accident to have occurred in the United States, and the second deadliest aviation crash involving a DC-10, behind Turkish Airlines Flight 981.
The National Transportation Safety Board (NTSB) found that as the jet was beginning its takeoff rotation, engine number one (the left engine) separated from the left wing, flipping over the top of the wing and landing on the runway. As the engine separated from the aircraft, it severed hydraulic fluid lines that locked the wing's leading edge slats in place and damaged a three-foot section of the left wing's leading edge. Aerodynamic forces acting on the wing resulted in an uncommanded retraction of the outboard slats. As the jet began to climb, the damaged left wing, with no engine, produced far less lift (stalled) than the right wing, with its slats still deployed and its engine running at full takeoff speed. The disrupted and unbalanced aerodynamics of the aircraft caused it to roll abruptly to the left until it was partially inverted, reaching a bank angle of 112 degrees, before crashing in an open field by a trailer park near the end of the runway. The engine separation was attributed to damage to the pylon structure holding the engine to the wing, caused by improper maintenance procedures used at American Airlines.
Accident
Air Crash Investigation American Airlines Flight 191 "Americas Deadliest Air Crash" -
On the accident flight, just as the aircraft reached takeoff speed, the No.1 Engine and its pylon assembly separated from the left wing, ripping away a 3-foot (0.91Â m) section of the leading edge with it. The combined unit flipped over the top of the wing and landed on the runway. Robert Graham, supervisor of maintenance for American Airlines, stated: "As the aircraft got closer, I noticed what appeared to be vapor or smoke of some type coming from the leading edge of the wing and the No. 1 engine pylon. I noticed that the No. 1 engine was bouncing up and down quite a bit and just about the time the aircraft got opposite my position and started rotation, the engine came off, went up over the top of the wing, and rolled back down onto the runway... Before going over the wing, the engine went forward and up just as if it had lift and was actually climbing. It didn't strike the top of the wing on its way, rather it followed the clear path of the airflow of the wing, up and over the top of it, then down below the tail. The aircraft continued a fairly normal climb until it started a turn to the left. And at that point, I thought he was going to come back to the airport."
It is not known what was said in the cockpit in the 50 seconds leading up to final impact, as the cockpit voice recorder lost power when the engine detached. The only crash-related audio collected by the recorder is a thumping noise (likely the sound of the engine separating), followed by the first officer exclaiming "Damn!", at which point the recording ends. This may also explain why Air Traffic Control was unsuccessful in their attempts to radio the crew and inform them that they had lost an engine. This loss of power did, however, prove useful in the investigation, serving as a marker of exactly what circuit in the DC-10's extensive electrical system had failed.
In addition to the engine's failure, several related systems failed. The number one hydraulic system, powered by the number one engine, failed but continued to operate via motor pumps that mechanically connected it to hydraulic system three. Hydraulic system three was also damaged and began leaking fluid but maintained pressure and operation up until impact. Hydraulic system two was undamaged. The number one electrical bus, whose generator was attached to the number one engine, failed, causing several electrical systems to go offline, most notably the captain's instruments, his stick shaker, and the slat disagreement sensors. While a switch in the overhead panel would have allowed the captain to restore power to his instruments, it was not used. It might have been possible for the flight engineer to reach the backup power switch (as part of an abnormal situation checklist â€" not as part of their take-off emergency procedure) in an effort to restore electrical power to the number one electrical bus. That would have worked only if electrical faults were no longer present in the number one electrical system. Furthermore, to reach the switch the flight engineer would have had to rotate his seat, release his safety belt, and stand up. Since the aircraft never got higher than 350 feet (110 m) above ground and was in the air for only 50 seconds between when the engine separated and when it crashed, there was not sufficient time to take such an action. In any event, the first officer was flying the airplane and his instruments continued to function normally. As the wings and engines were not visible from the cockpit, the crew likely had no idea that an engine had fallen off, only that one had failed.
Since it was no longer possible to abort the takeoff at this point, the crew followed the standard operating procedure for an "engine out" climb. This procedure is to climb at the takeoff safety airspeed (V2) and attitude (angle), as directed by the flight director. The partial electrical power failure (produced by the separation of the left No. 1 engine) meant that neither the stall warning nor slat retraction indicator was operative. The crew was, therefore, unaware that the slats on the left wing were retracting. This retraction significantly raised the stall speed of the left wing. Thus flying at the takeoff safety airspeed caused the left wing to stall while the right wing was still producing lift, so the aircraft banked sharply and uncontrollably to the left. Later, in simulator recreations of the accident, it was determined that if they had climbed at a higher airspeed the crash could have been averted.
The aircraft climbed to about 325 feet (99Â m) above ground level while spewing a white mist trail of fuel and hydraulic fluid from the left wing. The first officer had followed the flight director and raised the nose to 14Â degrees, which reduced the airspeed from 165 knots (190Â mph; 306Â km/h) to the takeoff safety airspeed (V2) of 153 knots (176Â mph; 283Â km/h), the speed at which the aircraft could safely climb after sustaining an engine failure. However, the engine separation had severed the hydraulic fluid lines that controlled the leading edge slats on the left wing and locked them in place, causing the outboard slats (immediately left of the No. 1 engine) to retract under air load. The retraction of the slats raised the stall speed of the left wing to approximately 159 knots (183Â mph; 294Â km/h), 6 knots (6.9Â mph; 11Â km/h) higher than the prescribed takeoff safety airspeed (V2) of 153 knots (176Â mph; 283Â km/h). As a result, the left wing entered a full aerodynamic stall.
With the left wing stalled the aircraft began banking to the left, rolling over onto its side until it was partially inverted at a 112-degree bank angle (as seen in the Laughlin photograph) with its right wing over its left wing. As the cockpit had been equipped with a closed-circuit television camera positioned behind the captain's shoulder and connected to view screens in the passenger cabin, it is possible that passengers were able to witness these events from the cockpit as the aircraft dove towards the ground. Whether the camera's view was interrupted by the power loss from the number one electrical bus is not known. The aircraft eventually slammed into a field approximately 4,600Â ft (1,400Â m) from the end of the runway. Large sections of aircraft debris were hurled by the force of the impact into an adjacent trailer park, destroying five trailers and several cars. The DC-10 had also crashed into an old aircraft hangar located at the edge of the airport at the former site of Ravenswood Airport, which was used for storage.
In addition to the 271 people on board the aircraft, two employees at a nearby repair garage were killed and two more severely burned. The crash scene is a field northwest of the intersection of Touhy Avenue (Illinois Route 72) and Mount Prospect Road on the border of the suburbs of Des Plaines and Mount Prospect, Illinois.
Investigation
The aircraft involved was a McDonnell Douglas DC-10-10 registered N110AA. It had been delivered on February 25, 1972, and at the time of the crash, it had logged just under 20,000 hours of flying time over seven years. The jet was powered by three General Electric CF6-6D engines. A review of the aircraft's flight logs and maintenance records showed that no mechanical discrepancies were noted for May 11, 1979. On the day of the accident, in violation of standard procedure, the records were not removed from the aircraft, and were destroyed in the accident.
The disaster and investigation received widespread media coverage. The impact on the public was increased by the dramatic effect of an amateur photo taken of the aircraft rolling that was published on the front page of the Chicago Tribune on the Sunday two days after the crash. There were some early reports that a collision with a small aircraft had been the cause of the crash. This apparently was the result of the discovery of small-aircraft parts among the wreckage at the crash site. National Transportation Safety Board vice-chairman Elwood T. Driver, in a press briefing, was photographed holding a broken bolt and nut, implying that these parts were a cause of the accident. The small-plane parts were subsequently determined to have been on the ground at the time of the crash, at the former general aviation Ravenswood Airport, a facility that had been out of service for a few years. An owner there had been selling used aircraft parts from a remaining hangar building.
The NTSB determined that the loss of one engine and the asymmetrical drag caused by damage to the wing's leading edge should not have been enough to cause the pilots to lose control of their aircraft; the aircraft should have been capable of returning to the airport using its remaining two engines. The NTSB thus examined the effects that the engine's separation would have on the aircraft's flight control, hydraulic, electrical, and instrumentation systems. Unlike other aircraft designs, the DC-10 did not include a separate mechanism to lock the extended leading edge slats in place, relying instead solely on the hydraulic pressure within the system. The NTSB determined that the engine tore through multiple hydraulic lines as it separated from the DC-10's wing, causing a loss of hydraulic pressure; airflow over the wings forced the left wing slats to retract, which caused a stall over the left wing. In response to the accident, slat relief valves were mandated to prevent slat retraction in case of hydraulic line damage.
The wreckage was too severely fragmented to determine the exact position of the rudders, elevators, flaps, and slats before impact and examination of eyewitness photographs showed only that the right wing slats were fully extended as the crew tried unsuccessfully to correct the steep roll they were in. The left wing slats could not be determined from the blurry color photographs, so they were sent to a laboratory in Palo Alto, California for digital analysis, a process that was pushing the limits of 1970s technology and necessitated large, complicated, and expensive equipment. The photographs were reduced to black-and-white, which made it possible to distinguish the slats from the wing itself and thus proved that they were retracted. In addition, it was also verified that the tail section of the aircraft was undamaged and the landing gear was down.
Wind tunnel and flight simulator tests were conducted to help to understand the trajectory of the aircraft after the engine detached and the left wing slats retracted. Those tests established that the damage to the wing's leading edge and retraction of the slats increased the stall speed of the left wing from 124 knots (143Â mph) to 159 knots (183Â mph). The DC-10 incorporates two warning devices that might have alerted the pilots to the impending stall: the slat disagreement warning light, which should have illuminated after the uncommanded retraction of the slats, and the stick shaker on the captain's control column, which activates close to the stall speed. Both of these warning devices were powered by an electric generator driven by the number one engine. Both systems became inoperative after the loss of that engine. The first officer's control column was not equipped with a stick shaker; the device was offered by McDonnell Douglas as an option for the first officer, but American Airlines chose not to have it installed on its DC-10 fleet. Stick shakers for both pilots became mandatory in response to this accident.
Engine separation
Witnesses to the crash were in universal agreement that the aircraft had not struck any foreign objects on the runway. Also, no pieces of the wing or other aircraft components were found along with the separated engine, other than its supporting pylon, leading investigators to conclude that nothing else had broken free from the airframe and struck the engine. Hence, the engine/pylon assembly separation could only have resulted from a structural failure.
During the investigation, an examination on the pylon attachment points revealed some damage done to the wing's pylon mounting bracket that matched the shape of the pylon's rear attachment fitting. This meant that the pylon attachment fitting had struck the mounting bracket at some point. This was some important evidence, as the only way the pylon fitting could strike the wing's mounting bracket in the observed manner was if the bolts that held the pylon to the wing had been removed and the engine/pylon assembly was being supported by something other than the aircraft itself. Therefore, investigators now could conclude that the observed damage to the rear pylon mount had been present before the crash actually occurred, rather than being caused by it.
The NTSB determined that the damage to the left wing engine pylon had occurred during an earlier engine change at the American Airlines aircraft maintenance facility in Tulsa, Oklahoma, between March 29 and 30, 1979. On those dates, the aircraft had undergone routine service, during which the engine and pylon had been removed from the wing for inspection and maintenance. The removal procedure recommended by McDonnell-Douglas called for the engine to be detached from the pylon before detaching the pylon itself from the wing. However, American Airlines, as well as Continental Airlines and United Airlines, had developed a different procedure that saved approximately 200 man-hours per aircraft and "more importantly from a safety standpoint, it would reduce the number of disconnects (of systems such as hydraulic and fuel lines, electrical cables, and wiring) from 72 to 27." This new procedure involved the removal of the engine and pylon assembly as a single unit, rather than as individual components. United Airlines' implementation involved the use of an overhead crane to support the engine/pylon assembly during removal and installation. The method chosen by American and Continental's procedures supported the engine/pylon assembly with the hold of a large forklift.
It was learned that if the forklift were incorrectly positioned, the engine/pylon assembly would not be stable as it was being handled, causing it to rock like a see-saw and jam the pylon against the wing's attachment points. The forklift operator was guided only by hand and voice signals, as he or she could not directly see the juncture between pylon and wing. Positioning had to be extremely accurate or structural damage could result. Compounding the problem, maintenance work on N110AA did not go smoothly. The mechanics started to disconnect the engine and pylon, but there was a shift change halfway through the job. When work was resumed, the pylon was jammed on the wing and the forklift had to be re-positioned, resulting in unseen structural damage to the wing's pylon attachment points. The structural damage was not enough to cause an immediate failure. However, the damage to the mount developed into fatigue cracking, and worsened with each takeoff and landing cycle during the eight weeks that followed the maintenance on N110AA. Finally, the damaged rear pylon mount was weakened to such an extent that it was no longer able to support even normal flight loads, and failed. Due to the absence of this attachment, the engine, at full takeoff power, and its pylon fell off the wing. The structure surrounding the forward pylon mount then failed from the resulting stresses.
Inspection of the DC-10 fleets of the three airlines revealed that while United Airlines' hoist approach seemed to be harmless, there were several DC-10s at both American and Continental that already had fatal damage to their pylon mounts. The field service representative from McDonnell-Douglas stated the company would "not encourage this procedure due to the element of risk" and had so advised American Airlines. McDonnell-Douglas, however, "does not have the authority to either approve or disapprove the maintenance procedures of its customers."
Probable cause
The findings of the investigation by the National Transportation Safety Board were released on December 21, 1979:
The National Transportation Safety Board determines that the probable cause of this accident was the asymmetrical stall and the ensuing roll of the aircraft because of the uncommanded retraction of the left wing outboard leading edge slats and the loss of stall warning and slat disagreement indication systems resulting from maintenance-induced damage leading to the separation of the No. 1 engine and pylon assembly at a critical point during takeoff. The separation resulted from damage by improper maintenance procedures which led to failure of the pylon structure.
Contributing to the cause of the accident were the vulnerability of the design of the pylon attach points to maintenance damage; the vulnerability of the design of the leading edge slat system to the damage which produced asymmetry; deficiencies in Federal Aviation Administration surveillance and reporting systems which failed to detect and prevent the use of improper maintenance procedures; deficiencies in the practices and communications among the operators, the manufacturer, and the FAA which failed to determine and disseminate the particulars regarding previous maintenance damage incidents; and the intolerance of prescribed operational procedures to this unique emergency.
Legacy of the DC-10
The crash of Flight 191 brought strong criticism from the media regarding the DC-10's safety and design. The DC-10 had been involved in two accidents related to the design of its cargo doors, American Airlines Flight 96 (1972) and Turkish Airlines Flight 981 (1974). The separation of engine one from its mount, the widespread publication of the dramatic images of the airplane missing its engine seconds before the crash, and a second photo of the fireball resulting from the impact, raised widespread concerns about the safety of the DC-10. The final blow to the airplane's reputation was dealt two weeks after the crash, when the aircraft was grounded by the FAA. Although the aircraft itself was later exonerated, the damage in the public's eye was already done.
The investigation also revealed other DC-10s with damage caused by the same faulty maintenance procedure. The faulty procedure was banned, and the aircraft type went on to have a long career as a passenger and cargo aircraft. In response to this accident, American Airlines was fined $500,000 by the U.S. government for improper maintenance procedures.
On June 6, 1979, two weeks after the crash, the Federal Aviation Administration suspended the type certificate for the DC-10, thereby grounding all DC-10s under its jurisdiction. It also enacted a special air regulation banning the DC-10 from U.S. airspace, which prevented foreign DC-10s not under the jurisdiction of the FAA from flying within the country. This was done while the FAA investigated whether or not the airplane's engine mounting and pylon design met relevant requirements. Once the FAA was satisfied that maintenance issues were primarily at fault and not the actual design of the aircraft, the type certificate was restored on July 13 and the special air regulation repealed. However, the type certificate was amended, stating that "...removal of the engine and pylon as a unit will immediately render the aircraft un-airworthy."
Another DC-10, performing Western Airlines Flight 2605, crashed in Mexico City after a red-eye flight from Los Angeles barely 5 months after the crash of American Airlines Flight 191. The Western Airlines DC-10's crash, however, was due to low visibility and an attempt to land on a closed runway. Ironically, the crash of yet another DC-10, United Airlines Flight 232, ten years later, restored some of the aircraft's reputation. Despite losing an engine, all flight controls, crash-landing in a huge fireball (which was caught on video by a local news crew), and killing 111 people, 185 people survived the accident. Experts praised the DC-10's sturdy construction as partly responsible for the high number of survivors, though the efforts of the crew were primarily responsible.
The crash of yet another DC-10 at the end of November, Air New Zealand Flight 901, exactly six months after Flight 191, added to the DC-10's negative reputation. The crash of Flight 901, an Antarctic sightseeing flight which hit a mountain, was caused by several human and environmental factors not related to the airworthiness of the DC-10, and the aircraft was later completely exonerated in that accident.
Despite initial safety concerns, DC-10 aircraft continued to serve with passenger airlines for over 30 years after the crash of Flight 191. In the end, it was newer, more fuel-efficient twin-engined airplanes from Boeing and Airbus and not safety concerns that ultimately ended the passenger career of the DC-10 (however, the safety concerns did ultimately end the DC-10's production in 1983). Many retired passenger DC-10s have since been converted to all-cargo use. DC-10 freighters, along with its derivative, the MD-11, form the backbone of the FedEx Express fleet. The DC-10s have been upgraded with the glass cockpit from the MD-11, thereby turning them into MD-10s. American Airlines retired its last DC-10s in 2000 after 29 years of service. In February 2014, Biman Bangladesh Airlines operated the final DC-10 passenger flights. DC-10s continue to be used extensively in air freight operations, and military variants also remain in service.
Victims
Nationalities of the passengers and crew
Flight crew
Captain Walter Lux, 53, had been flying the DC-10 since its introduction eight years earlier. He had logged around 22,000 flying hours, of which about 3,000 were in a DC-10. He was also qualified to pilot 17 other aircraft, including the DC-6, DC-7, and Boeing 727. First Officer James Dillard, 49, and Flight Engineer Alfred Udovich, 56, were also highly experienced: 9,275 hours and 15,000 hours respectively, and between them they had 1,830 hours flying experience in the DC-10.
Passengers
Some notable victims in the crash of Flight 191 were:
- Itzhak Bentov, a Czechoslovakia-born Israeliâ€"American biomedical inventor (the cardiac catheter) and New Age author (Stalking the Wild Pendulum and A Cosmic Book).
- Leonard Stogel, music business manager/promoter/producer/executive for California Jam and California Jam II, Sweathog, The Cowsills, Sam the Sham, Tommy James & The Shondells, Redbone, Gentle Giant, and other musical groups. Coincidentally, Stogel's parents had earlier perished on American Airlines Flight 1.
Memorial
For 32 years there was no permanent memorial to the victims. Funding was obtained for a memorial in 2009, through a two-year effort by the 6th grade class of Decatur Classical School in Chicago. The memorial, a 2-foot (0.6Â m)-high concave wall with interlocking bricks displaying the names of the crash victims, was formally dedicated in a ceremony on October 15, 2011. The memorial is located at Lake Park at the northwest corner of Lee and Touhy Avenues, two miles east of the crash site.
Depictions in media
The cable/satellite TV channel The National Geographic Channel produced a documentary on the crash, and an episode from Seconds from Disaster titled "Chicago Plane Crash" detailed the crash and included film of the investigation press conferences. The Canadian television series Mayday profiled the crash in the episode "Catastrophe at O'Hare", which has subsequently aired in the U.S. on the Smithsonian Channel's television series Air Disasters.
Chicago folk singer Steve Goodman wrote the song "Ballad of Flight 191 (They Know Everything About It)" in response to the crash and the subsequent investigation as the inaugural song for a series of topical songs which aired on National Public Radio in 1979. The Michael Crichton novel Airframe described the incident in detail as an example to the reader how a "good airplane (DC-10)" could be "destroyed by bad press".
See also
- Aviation accidents and incidents
- Aviation safety
- Similar accidents caused by engine separation
- China Airlines Flight 358
- El Al Flight 1862
References
External links
- NTSB Accident Report
- "Public Lessons Learned from Accidents â€" American Airlines Flight 191" (archive)
- PlaneCrashInfo.Com â€" American Airlines Flight 191
- Flight 191 Remembered (Fox Chicago website, archive)
- Pre-crash pictures from Airliners.net
- NTSB Probable Cause Report
- News reports at The Museum of Classic Chicago Television