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American Airlines Flight 191
American Airlines Flight 191 was a regularly scheduled passenger flight from O'Hare International Airport in Chicago to Los Angeles International Airport. On May 25, 1979, the McDonnell Douglas DC-10-10 operating the flight crashed moments after takeoff from Chicago. All 258 passengers and 13 crew on board were killed, along with two people on the ground. Until the September 11 attacks, it was the most devastating air disaster in the history of the United States. It remains the deadliest aviation accident to occur on U.S. soil,[note 1] as well as the second most devastating involving a DC-10, after Turkish Airlines Flight 981. It was also the third worst aviation disaster in history at the time, and is currently the tenth worst.
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 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 rigging structure holding the engine to the wing caused by faulty maintenance procedures at American Airlines.
While maintenance issues and not the actual design of the aircraft were ultimately 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 several other incidents and accidents involving the type. 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 passenger career. It has since found a second career as a cargo airplane.
InvestigationThe National Transportation Safety Board was responsible for investigating the accident. The safety board was assigned to determine why the engine separated from the airplane and why the airplane was unable to remain airborne on its two remaining engines.
The loss of the engine by itself should not have been enough to cause the accident; Flight 191 should have been capable of returning to the airport using its remaining two engines. Unlike other aircraft designs, however, 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. In response to the accident, slat relief valves were mandated to prevent slat retraction in case of hydraulic line damage.
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's leading edge and retraction of the slats increased the stall speed of the left wing from 124 knots to 159 knots.
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. 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 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 before 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." 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.
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. McDonnell Douglas, however, "does not have the authority to either approve or disapprove the maintenance procedures of its customers."
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 work, there were multiple DC-10s at both Continental and American with damage to their pylon mounts.
If the forklift was in the wrong position, as with the procedure used by American, 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 on 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.
Examination of the pylon attachment points after the crash 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 before the crash, rather than being caused by it.
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 reached the breaking point and failed. Without this fitting in place 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.
As one German banker can tell you, nodding off at your desk can cost you. In this case, a quick workplace nap almost cost one woman her job and caused a $293 million banking error.
The clerk “momentarily fell asleep” on the job and accidentally held down the number 2 button on his keyboard for a little too long — think 222,222,222.22 — causing that much money (in Euros) to be transferred out of the bank.
(MORE: Oregon Burglar Falls Asleep While Robbing a House)
While the mistake was eventually noticed and corrected, the on-duty supervisor originally approved the payment request, allowing the funds to go through. On further review of the supervisor’s records, it was discovered that the 48-year-old woman had spent less than 1.4 seconds to examine a total of 603 payments. She was fired for not catching the glaring error — although after bringing her case to court was given her job back — while the snoozing clerk was only handed a slap on the wrist.
So the next time you’re feeling a little drowsy on the job, you might want to take an extra cup of coffee instead of a power nap.
Read more: http://newsfeed.time.com/2013/06/15/on-the-job-nap-leads-to-293m-banking-error/#ixzz2WuH3hZz0