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Status: | Final |
Date: | Friday 25 May 1979 |
Time: | 15:04 |
Type: |
![]() McDonnell Douglas DC-10-10 |
Operator: | American Airlines |
Registration: | N110AA |
MSN: | 46510/22 |
First flight: | 1972 |
Total airframe hrs: | 19871 |
Engines: | 3 General Electric CF6-6D |
Crew: | Fatalities: 13 / Occupants: 13 |
Passengers: | Fatalities: 258 / Occupants: 258 |
Total: | Fatalities: 271 / Occupants: 271 |
Ground casualties: | Fatalities: 2 |
Aircraft damage: | Destroyed |
Aircraft fate: | Written off (damaged beyond repair) |
Location: | Chicago-O'Hare International Airport, IL (ORD) (![]() |
Crash site elevation: | 204 m (669 feet) amsl |
Phase: | Takeoff (TOF) |
Nature: | Domestic Scheduled Passenger |
Departure airport: | Chicago-O'Hare International Airport, IL (ORD/KORD), United States of America |
Destination airport: | Los Angeles International Airport, CA (LAX/KLAX), United States of America |
Flightnumber: | AA191 |
Narrative:
American Airlines Flight 191, a McDonnell-Douglas DC-10-10, crashed on takeoff from Chicago-O'Hare International Airport, Illinois, USA...
On the accident flight, just as the aircraft reached takeoff speed, the number-one engine and its pylon assembly separated from the left wing, ripping away a 3-foot (0.9 m) section of the leading edge with it. The combined unit flipped over the top of the wing and landed on the runway.[1]: 2 Robert Graham, supervisor of maintenance for American Airlines, stated:
What was said in the cockpit in the 50 seconds leading up to the final impact is not known, as the cockpit voice recorder (CVR) 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.[1]: 57As 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 number-one engine pylon. I noticed that the number-one 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.[9]
In addition to the engine's failure, several related systems failed. The number-one hydraulic system, powered by the number-one engine, also failed but continued to operate through 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 until impact. Hydraulic system two was undamaged. The number-one electrical bus, whose generator was attached to the number-one engine, failed, as well, causing several electrical systems to go offline, most notably the captain's instruments, his stick shaker, and the slat disagreement sensors. A switch in the overhead panel would have allowed the captain to restore power to his instruments, but it was not used. The flight engineer might have reached the backup power switch (as part of an abnormal situation checklist—not as part of their takeoff emergency procedure) 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. To reach that backup power switch, the flight engineer would have had to rotate his seat, release his safety belt, and stand up. Regardless, the aircraft did not get any higher than 350 feet (110 m) above the ground and was only in the air for 50 seconds between the time the engine separated and the moment it crashed; time was insufficient to perform such an action. In any event, the first officer was flying the airplane, and his instruments continued to function normally.[1]: 52
The aircraft climbed to about 325 feet (100 m) above ground level while spewing a white mist trail of fuel and hydraulic fluid from the left wing. The first officer followed the flight director and raised the nose to 14°, which reduced the airspeed from 165 knots (190 mph; 306 km/h) to the takeoff safety airspeed (V2) of 153 knots (176 mph; 283 km/h), the speed at which the aircraft could safely climb after sustaining an engine failure.[1]: 53–54
The engine separation 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 number-one engine) to retract under air load. The retraction of the slats raised the stall speed of the left wing to about 159 knots (183 mph; 294 km/h), 6 knots (6.9 mph; 11 km/h) higher than the prescribed takeoff safety airspeed (V2) of 153 knots. 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° bank angle (as seen in the Laughlin photograph) with its right wing over its left wing.
Since 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, the passengers may have witnessed these events from the viewpoint of the cockpit as the aircraft dove towards the ground.[10][11]
The No.1 engine pylon failure during takeoff was determined to have been caused by unintended structural damage which occurred during engine/pylon reinstallation using a forklift. The engine/pylon removal and reinstallation were being conducted to implement two DC-10 Service Bulletins. Both required that the pylons be removed, and recommended that this be accomplished with the engines removed. The Service Bulletin instructions assumed that engines and pylons would be removed separately, and did not provide instructions to remove the engine and pylon as a unit. Additionally, removal of the engines and pylons as a unit was not an approved Maintenance Manual procedure.
The lack of precision associated with the use of the forklift, essentially an inability to perform the fine manipulations necessary to accomplish reinstallation of the engine/strut assembly, in combination with the tight clearances between the pylon flange and the wing clevis resulted in damage to the same part that had just been inspected.
Inspections of other DC-10 pylon mounts following the accident resulted in nine additional cracked mounts being identified.
Probable Cause:
PROBABLE CAUSE: "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 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 FAA 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."
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