Michael Laughlin took this famous photograph from the viewing platform on Terminal 2 of O'Hare International Airport. It depicts Flight 191 in an unrecoverable bank moments before the crash. Its number one engine had separated from the aircraft while it was on the runway. |
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| Accident summary | |
|---|---|
| Date | May 25, 1979 |
| Type | Loss of control after engine detachment due to improper maintenance |
| Site | Des Plaines, Illinois, United States |
| Passengers | 258 |
| Crew | 13 |
| Fatalities | 273 (including 2 on ground) |
| Survivors | 0 |
| Aircraft type | McDonnell Douglas DC-10-10 |
| Operator | American Airlines |
| Tail number | N110AA |
| Flight origin | O'Hare International Airport |
| Destination | Los Angeles International Airport |
American Airlines Flight 191 was a regularly scheduled passenger flight in the United States from O'Hare International Airport in Chicago, Illinois, to Los Angeles International Airport. On May 25, 1979, the McDonnell Douglas DC-10-10 operating the route crashed moments after takeoff from Chicago. All 258 passengers and 13 crew on board were killed, along with two people on the ground. It was the deadliest air disaster in the history of the United States, as well as the second deadliest involving a DC-10, after Turkish Airlines Flight 981.[note 1]
Investigators found that as the jet was beginning its takeoff rotation, engine number one on the left (port) wing separated and flipped over the top of the wing. As the engine separated from the aircraft, it severed hydraulic fluid lines and damaged the left wing, resulting in a retraction of the slats. As the jet attempted to climb, the left wing aerodynamically stalled while the right wing, with its slats still deployed, continued to produce lift. The jetliner subsequently rolled to the left and reached a bank angle of 112 degrees (partially inverted), before impacting in an open field near a trailer park located near the end of the runway. The engine separation was attributed to damage to the pylon rigging structure holding the engine to the wing caused by inadequate maintenance procedures at American Airlines.
While maintenance issues and not the actual design of the aircraft would ultimately be found responsible for the crash, the accident and subsequent grounding of all DC-10s by the Federal Aviation Administration added to an already unfavorable reputation of the DC-10 aircraft in the eyes of the public caused by other unrelated accidents.
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The aircraft involved was a McDonnell Douglas DC-10-10. It had been delivered on February 25, 1972, and at the time of the crash had logged more than 20,000 hours of flight 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 24, 1979. On the day of the accident the records had not been removed from the aircraft, as was standard procedure, and were destroyed in the accident.[1]
The Captain was one of the most experienced DC-10 pilots in the airline; he had been flying the DC-10 since its introduction eight years earlier. He had around 22,000 hours logged, of which about 3,000 were in a DC-10. He was also qualified to pilot seventeen other aircraft, including the DC-6, DC-7, and Boeing 727.[1] The First Officer and Flight Engineer were also very experienced; they shared over 25,000 flying hours between them, of which 1,830 were in the DC-10.[2][3]
The weather was clear, with a northeast wind at 22 knots (41 km/h). At 14:50 CDT, Flight 191 pushed back from gate K5 and was cleared to taxi to runway 32R. Maintenance crews present at the gate did not notice anything unusual during pushback, engine start, or taxi.[1]
The flight began its takeoff roll at 15:02.[4] Everything appeared normal until just after VR (rotation speed),[note 2] when the number one engine and the pylon assembly that attached it to the wing separated from the aircraft, ripping away a 3 foot (0.91 m) section of the leading edge of the left wing in the process. Both the engine and pylon flipped over the top of the wing and landed on the runway.[1] As the airplane was already above V1 and at VR, the flight crew continued the takeoff. The airplane became airborne about 6,000 feet (1,800 m) down the 10,000-foot (3,000 m) runway at a speed well above V2.[1]
The pilots were aware that the number one engine had failed, but they could not have known it had fallen off the plane, because the wings and engines were not visible from the cockpit and the control tower did not inform the flight crew of the problem. Investigators subsequently concluded the flight crew thought engine one had only failed, not separated from the aircraft.[1]
In addition to the engine failure, several other related systems failed. The number one hydraulic system, powered by the number one engine, failed but continued to operate via motor pumps which 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 and as such several electrical systems went 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. In any event, the First Officer was flying the airplane and his instruments continued to function normally.[1]
Witnesses observed the aircraft continue to climb to about 300 feet (91 m) above ground level while spewing a white vapor trail of fuel and hydraulic fluid.[1] The first officer raised the nose up to 14 degrees to reduce the airspeed from 165 knots (306 km/h), to the V2 speed of 153 knots (283 km/h), the speed specified in the emergency procedure for engine failure during takeoff. However, the engine separation had severed the hydraulic fluid lines which controlled the leading edge slats on the left wing, causing the slats outboard (towards the tip of the wing) of the separated engine to retract under air load. The retraction of the slats raised the stall speed of the left wing to approximately 159 knots (294 km/h), 6 knots (11 km/h) higher than the prescribed V2 speed. As the aircraft reached V2, the left wing entered a full aerodynamic stall. The resulting asymmetric lift caused the plane to roll rapidly to the left and enter a steep dive from which it could not recover despite maximum opposite control inputs by the First Officer. Flight 191 crashed in a 112-degree bank into an open field approximately 4,600 ft (1,400 m) from the end of the runway.[1]
Large sections of aircraft debris were hurled by the force of the impact into an adjacent trailer park, destroying five trailers and several cars, and demolishing an old aircraft hangar at Ravenswood Airport that was used for storage.[5] The fuselage cut a trench into the empty former airfield and the large amount of jet fuel generated a huge fireball.[1]
The plume of smoke could be seen from the downtown Chicago Loop. A fireman assisting at the scene of the crash later stated, "We didn't see one body intact, just trunks, hands, arms, heads, and parts of legs. And we can't tell whether they were male or female, or whether they were adult or child, because they were all charred."[5] Another first responder on the scene stated, "It was too hot to touch anybody and I really couldn't tell if they were men or women. Bodies were scattered all over the field."[5]
All 271 passengers and crew on board were killed by the impact and subsequent fire, making it the deadliest aviation accident in the United States to date.[note 1][6] On the ground, two employees at a repair garage were killed and two more severely burned. Of the 273 victims, only about a dozen bodies were left intact.[5] Three additional residents were injured from falling aircraft debris. The airplane crashed in a field northwest of the intersection of Touhy Ave. (Illinois Route 72) and Mt. Prospect Road, on the border of Des Plaines and Mount Prospect, Illinois.[1]
The National Transportation Safety Board was responsible for investigating the accident. The safety board was tasked with determining why the engine separated from the airplane and why the airplane was unable to remain airborne on its two remaining engines.[1]
The loss of the engine by itself should not have been enough to cause the accident;[7] Flight 191 should have been capable of returning to the airport using its remaining two engines.[1] However, 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.[1] In response to the accident, slat relief valves were mandated to prevent slat retraction in case of hydraulic line damage.[8]
Wind tunnel and flight simulator tests were conducted to help to understand the trajectory of flight 191 after the engine detached and the left wing slats retracted. Those tests established that the damage to the wing leading edge and retraction of the slats increased the stall speed of the left wing from 124 knots to 159 knots.[1]
The DC-10 incorporates two warning devices which 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. Unfortunately, both of these warning devices were powered by an electric generator driven by the number one engine; following the loss of that engine, both systems became inoperative.[1] 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 their DC-10 fleet. Stick shakers for both pilots became mandatory in response to this accident.[9]
From an examination of the detached engine, the NTSB concluded that the pylon attachment had been damaged before the crash.[1] Investigators looked at the plane's maintenance history and found that its most recent service was eight weeks before the crash, in which engine number one had been removed from the aircraft. The pylon, the rigging holding the engine onto the wing, had been damaged during the procedure. The procedure recommended by McDonnell Douglas called for the engine to be removed from the pylon prior to detaching the pylon itself, but American Airlines, along with Continental Airlines and United Airlines, had begun to use a 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."[1] The new procedure involved mechanics removing the engine with the pylon and engine as a single unit. A large forklift was used to support the engine while it was being detached from the wing – a procedure that was found to be extremely difficult to execute successfully, due to difficulties with holding the engine assembly straight while it was being removed.[1]
The field service representative from McDonnell Douglas said the company would "not encourage this procedure due to the element of risk" and had so advised American Airlines. However, McDonnell Douglas "does not have the authority to either approve or disapprove the maintenance procedures of its customers."[1]
The accident investigation also concluded that the design of the pylon and adjacent surfaces made the parts difficult to service and prone to damage by maintenance crews. The NTSB reported that there were two different approaches to the one-step procedure: using an overhead hoist or using a forklift. United Airlines used a hoist; American and Continental Airlines used a forklift. An examination of the DC-10 fleets of the three airlines showed that while United Airlines' hoist approach seemed to be working successfully, there were multiple DC-10s at both Continental and American with damage to their pylon mounts.[1]
Under the procedure American used, if the forklift was in the wrong position, the engine would rock like a see-saw and jam against the pylon attachment points. The forklift operator was guided by hand and voice signals; the positioning had to be perfect or damage could result. The maintenance to the aircraft involved in Flight 191 did not go smoothly. Aircraft mechanics started to disconnect the engine and pylon, but changed shift halfway through. When work continued, the pylon was jammed on the wing and the forklift had to be repositioned.[1]
After the crash, examination of the pylon attachment points revealed damage 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 pylon mounting bracket. This was important evidence because the only way the pylon fitting could strike the wing's mounting bracket in the observed manner was if the bolts holding the pylon to the wing were removed and if the engine was being supported by something other than the aircraft. Hence investigators were able to determine that the observed damage to the rear pylon mount existed prior to the crash, rather than being caused by it.[1]
The damage was not enough to cause an immediate failure; a fatigue crack developed and got worse with each flight. During flight 191's takeoff, the damaged rear pylon mount finally reached the breaking point and failed. Without this fitting, the engine at full takeoff thrust rotated upward on its still-attached forward pylon mount. The structure surrounding the forward pylon mount then overloaded and failed, and the engine went over the top of the wing and landed on the runway.[1]
The disaster and investigation received widespread coverage in the media, assisted by new news gathering technologies. The impact on the public was increased by the dramatic effect of an amateur photo taken of the plane rolling which was published on the front page of the Chicago Tribune the Sunday following the crash (the crash was on a Friday) [10]
There were some early reports that a collision with a small plane 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,[11] implying 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 which had been out of service for a few years. An owner there had been selling used aircraft parts from a remaining hangar building.[12]
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 and about to 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 would later be exonerated, the damage in the public's eye was already done.[13]
The findings of the investigation by the National Transportation Safety Board were released on December 21, 1979:[1]
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.
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 on March 29 and 30, 1979.[1] The evidence came from the flange, a critical part of the pylon assembly.
Problems with DC-10s were discovered as a cause of the accident, including deficiencies in design specifications and maintenance procedures which made damage very likely. In response to this accident, American Airlines was fined $500,000 by the United States government for improper maintenance procedures.[7]
On June 6, 1979, two weeks after the accident, the Federal Aviation Administration suspended the type certificate for the DC-10, thereby grounding all examples of the jet under its jurisdiction. Additionally a special air regulation was enacted prohibiting the DC-10 from operating within U.S. airspace, which prevented foreign DC-10s not under the jurisdiction of the FAA from flying within the country.[1] This was done while the FAA investigated whether or not the airplane's engine mount 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.[14]
The crash of another DC-10 in November 1979, Air New Zealand Flight 901, would only add to the DC-10's negative reputation at the time. 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.[15]
Ironically, the 1989 crash of another DC-10, United Airlines Flight 232, would serve to restore some of the aircraft's reputation. Despite losing an engine and all flight controls and crash-landing in a huge fireball (which was caught on video by a local news crew), 185 people would survive the accident. Experts praised the DC-10's sturdy construction as partly responsible for the high number of survivors.[13]
Despite the initial safety concerns, the DC-10 would continue to serve with passenger airlines until the mid 2000s. It was the introduction of newer, more fuel efficient twin-engine airplanes and not safety concerns which would ultimately end the passenger career of the DC-10.[13] Many retired passenger DC-10s have since been converted to all-cargo use. Modified passenger DC-10s, along with the newer variant, the MD-11, form the backbone of the FedEx Express fleet.[16] The DC-10s have been upgraded with the glass cockpit from the MD-11, thereby turning them into MD-10s.[17]
Some notable victims in the crash of Flight 191 were:
For over 30 years there was no permanent memorial at the crash site, in part because American Airlines would not release the names of the passengers who died in the accident. Funding was obtained for a memorial in 2009, through a two-year effort by a group of schoolchildren from Decatur Classical School.[20] The memorial, a two-foot concave shaped wall with interlocking bricks containing the names of the crash victims, was formally dedicated in a ceremony on October 15, 2011.[21]
The cable/satellite TV channel The History Channel produced a documentary on the crash,[22] and an episode from Seconds From Disaster titled "Chicago Plane Crash"[7] (also known as "Flight Engine Down") detailed the crash and included film of the investigation press conferences.
Following the crash and the media attention that was focused on the DC-10, American Airlines replaced all "DC-10 LuxuryLiner" titles on the fuselage with a more generic "American Airlines LuxuryLiner".[23]
In the days following the crash, a man named Clarence Bean, Jr., claimed that his girlfriend, Diane Chorba, was on the flight, but Cook County medical examiners assigned the task of identifying the crash victims later disproved this. Bean was found guilty of her murder in 2001.[24]
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.[25]
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