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The first in a series on the historical parallels and lessons that unite the groundings of the DC-10 and 737 Max.
As the engine tore away from American Airlines Flight 191 — flipping up and over the top of the left wing — the jet’s hydraulic lines installed inside the McDonnell Douglas DC-10’s leading edge ruptured. An electrical generator went with the departing engine. It was a catastrophic failure of the highest order and one that McDonnell Douglas had convinced itself and the Federal Aviation Administration could not happen.
Taking off from Chicago’s O’Hare Airport on May 25, 1979, the trijet made it to about 325 feet as it began a violent to roll to the left. Lacking hydraulic pressure, aerodynamic forces had slammed a portion of the left wing’s slats back into the retracted position. The generator, which was left on the runway along with the engine, no longer provided electricity to signal the crew that its slats were asymmetrically configured. The severed electrical connection also disabled the aircraft’s stall warning system.
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With an engine missing, the crew went by the book. The nose was raised to V2, the best speed to safely climb away from the ground. In any trained engine failure this was the right call every time given the information they had — trade airspeed for altitude — but the crew couldn’t see that the number one engine was gone, nor that a portion of its wing slats had retracted without hydraulic pressure. Without those slats, that V2 speed target was six knots below the stall speed of the left wing. When the left wing stalled, the unpowered stickshaker designed to alert the pilot in the left seat remained silent. A second stickshaker on the first-officer’s side was a customer option that American hadn’t purchased.
Resource: Read the complete NTSB report on American Airlines 191
All two hundred and seventy-one people aboard the aircraft and two on the ground were killed when the DC-10 crashed into a trailer park and an open field northwest of the airport.
On June 6, all 138 DC-10s at eight U.S. airlines were ordered grounded by the FAA when it revoked the jet’s airworthiness certificate and would stay that way for 37 days in 1979. The FAA initially opposed the grounding and the crash forced a legal battle with the American Airline Passengers Association, which sought an injunction to halt DC-10 flying in the U.S. “pending fuller analysis,” according to coverage in Flight. Inspections in the days that followed the Chicago crash revealed cracks on the engine pylons on other aircraft. FAA Administrator Langhorne Bond had no choice but to withdraw the roughly 275-seat jet’s airworthiness certificate. Carriers and regulators around the world — totaling some 274 aircraft, including 74 in Europe — followed suit.
McDonnell Douglas called the order “an extreme and unwarranted act.”
Aviation history remembers the cause of Flight 191 as a faulty maintenance procedure devised by airlines to save time when removing an engine. Douglas Aircraft Company, the civil airliner arm of McDonnell Douglas, had called for splitting the task – removing the General Electric CF6 engine and then the pylon — but American saved 200 man-hours with a single maneuver. As a result, the flange that attached two of the jet’s three engines developed cracks. Several hundred takeoffs and landings later the engine separated on Flight 191’s takeoff.Subscribe to TAC
Indeed, the pylon damage was the central trigger for the engine detaching from the wing. However, the National Transportation Safety Board concluded the maintenance practice that damaged the pylon only contributed to the cause of the crash. In recreating the circumstances of Flight 191 in a simulator, the NTSB and pilots concluded that with the warning systems operating, the catastrophic loss of an engine and even the slat retraction were inherently survivable. “Each by itself would not have caused a qualified flight crew to lose control of its aircraft,” according to the Safety Board’s final report. It was the loss of the warning and indication systems that ultimately caused the airplane to veer out of control.
As part of the conditions of its return to service, the FAA ordered all DC-10s to incorporate a redundant stall warning system that relied on two angle of attack sensors and ensure the integrity of its wing slat position alerts. And within 1,500 hours of flying again, each DC-10 cockpit needed two stickshaker motors fed by data from both speed computers. (Locking slats wouldn’t be mandated until 1982 after two more incidents involving failed engines on the DC-10)
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The grounding of the DC-10 ignited a debate over system redundancy, crew alerting, requirements for certification, and insufficient oversight and expertise of an under-resourced regulator — all familiar topics that are today at the center of the 737 Max grounding. To revisit the events of 40 years ago is to revisit a safety crisis that, swapping a few specific details, presents striking similarities four decades later, all the way down to the verbiage.
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