American Airlines Flight 191: the Worst Aviation Accident in US History

American Airlines Flight 191 should have been a standard flight from Chicago to Los Angeles. Instead, the name conjures horrifying visions of an aircraft in distress, a flight crew unable to recover, and the last moments of 273 lives.

The DC-10: A Troubled History

Introduced on August 5, 1971, McDonnell Douglas designed the DC-10 as a smaller, more fuel-efficient alternative to Boeing’s 747. Though its capacity for passengers lagged compared to its larger rival, the 3-engine DC-10 was also more efficient than the 4-engine 747. The idea of an intermediate, widebody aircraft was a popular one and McDonnell Douglas received 55 orders—25 to American Airlines and 30 to United.

American Airlines Flight 191
The accident aircraft

One design feature that received widespread attention was the DC-10’s cargo door. Whereas other airlines had cargo doors that opened inward, the DC-10’s cargo door opened outward. This ensured that no cargo space went to waste, an enticing proposal to potential customers. There was, however, a drawback that came with this design: the outward force of pressurization at altitude makes these types of doors susceptible to failure and explosive decompression. To counteract this force, such doors must be equipped with a heavy locking mechanism.

On June 12, 1972, the first failure in this system became apparent.

American Airlines Flight 96 was nearing the end of its route from Los Angeles To New York City. After a stop in Detroit, the plane began climbing towards its assigned altitude when its aft cargo door opened and broke off. The subsequent decompression led to a partial collapse of the cabin floor which damaged several control cables that ran beneath.

Luckily, there was no damage to the hydraulic systems, so the flight crew was able to maintain some manner of control. The aircraft was able to make an emergency landing back in Detroit and, while 11 people suffered injuries, there were no fatalities. The investigation into the accident determined that the actuator motors used to rotate the pins in the cargo door’s locking system had not completed its rotation. This was likely due to insufficient voltage to the motor. The ground crew would have heard the motor engage and run, assuming that the door was safely secured once the motor stopped.

First Fatalities

On March 3, 1974, a Turkish Airlines DC-10 took off from Istanbul, destined for London. After a stop at Paris’ Orly International Airport, the flight departed and began climbing out. Shortly after being cleared to 23,000 feet, one of the rear cargo doors blew out, taking with it a section of the cabin floor and 6 passengers.

As in Flight 96’s case, the cabin floor collapsed; this time, however, the control cables were completely severed. The flight crew fought for control of the stricken aircraft but were unable to save it. Just over one minute after the emergency began, the DC-10 crashed into the Ermenonville Forest. All 346 occupants (335 passengers, 11 crew) were killed.

While this accident is similar to the earlier American Airlines accident, the investigation turned up one very important piece of information. A ground crew—encountering issues with closing the door—had filed down the locking pins. As a result, the door—which was designed to withstand 300 psi—failed when met with only 15 psi.

This isn’t to absolve McDonnell Douglas, only to point out a mitigating factor.

This accident led to a complete overhaul of the DC-10’s cargo door locking mechanism, a redesign that sought to prevent uncontrolled movement of the locking pins.

The accident also opened McDonnell Douglas up to several lawsuits from families of the victims while creating public scrutiny around the safety of the DC-10.

American Airlines Flight 191

On May 25, 1979, Captain Walter Lux flew into Chicago O’Hare, set to spend Memorial Day Weekend with his family. Instead, a colleague with a family emergency approaches him with a request: take over Flight 191, bound for Los Angeles. Lux accepts and heads off to prepare for the unexpected flight.

Passengers begin boarding the plane on this beautiful and clear Chicago afternoon. Being a holiday weekend, the plane begins filling up. Lux meets his flight crew: First Officer James Dillard and Flight Engineer Alfred Udovich. The trio has over 45,000 combined flight time, 1,800 of them in the DC-10. They comprise an experienced flight crew, one any passenger would feel at ease with.

At 3:04 pm, American Airlines Flight 191 began its takeoff roll on runway 32R.

V1.

V2.

Just before rotation, the pylon that held the #1 engine to the left wing failed. As the nose of the plane lifted, the engine began to detach, swinging forward and carrying over the wing’s leading edge before breaking free.

A thud is heard in the cockpit and Dillard—the pilot in control during this stage of the flight—realizes that something is wrong. The cockpit voice recorder picks up a single word from the first officer:

“Damn.”

Following this, the recorder goes silent as it draws power from the now-detached #1 engine.

Below the Horizon

American Airlines Flight 191 continues to climb as the flight crew struggles to ascertain the situation. They know that the engine has failed, however, they are unaware that it has broken free of the aircraft. This isn’t quite as severe as it sounds, since this is how the engine should behave following such a failure.

The plane continues to slowly climb, the flight crew likely planning a return and emergency landing at O’Hare.

Outside, on the left wing, the slats have retracted. Used to increase lift at slower speeds, slats are key components during takeoff and the initial climb. Once they retract, the left wing loses lift. Compounding the issue, Dillard reduces speed, intending to complete a go-around and land back at the airport.

The intact right wing, meanwhile, continues generating lift as its slats remain extended. The plane begins banking to its left, entering an asymmetrical stall. It reaches a maximum altitude of 325 feet before it begins falling from the sky.

The leftward bank carries the DC-10 towards a series of warehouses near the edge of the airport; just beyond sat the Oasis trailer park.

Things were bad, on the verge of becoming much, much worse.

Flight 191 Down

The struggling aircraft banks towards a field, its left-hand wing contacting the ground just before the fuselage follows suit. The plane—loaded with fuel for the trip to Los Angeles—explodes in a massive fireball.

The explosion destroyed an old hangar, a mobile home, and several vehicles. The DC-10 was also destroyed, killing all 271 aboard. Two employees at a repair facility also perished while two others suffered extensive burns. This became the deadliest air disaster in US history, supplanting the September 1978 crash of PSA Flight 182.

The National Transportation Safety Board (NTSB) was quickly dispatched to the site to begin their investigation. On top of collecting pieces of the plane, they interviewed witnesses and studied photographs of the incident (seen in the tweets above). It was immediately apparent that the #1 engine—still sitting on the runway—had broken free, but the DC-10 should have been able to maintain safe flight, at least long enough to return for an emergency landing.

Investigators were left with two primary questions: why had the engine detached and why hadn’t the pilots been able to keep the plane in the air?

The Investigation

Initially, a fractured bolt and nut assembly belonging to the pylon was found and believed to be at the root of the accident. This was ruled out, leaving the obvious cause of separation to be a structural failure.

Once again a wave of negative public perception washed over both McDonnell Douglas and the DC-10. On June 6, 1979—in the midst of the investigation—the FAA withdrew the aircraft’s type certificate, grounding all US-based DC-10s while also restricting all international flights using the aircraft from entering US airspace.

The pylon attachment was found to bear impact damage that matched a piece of hardware used to mount it. This discovery meant that the pylon itself was loose and that this newly-discovered damage had been incurred before the accident.

Determined to get to the root of the problem, investigators observed an American Airlines maintenance crew removing an engine from another DC-10 for servicing. McDonnell Douglas recommended that the engine be removed directly from the pylon before removal of the pylon itself. This was a very labor-intensive endeavor, one with several points of contact (lines for hydraulics, electricity, and fuel) having to be disconnected.

What the investigators witnessed was the crew remove the engine and pylon as one piece. This procedure had been adopted by three airlines (American, Continental, and United) in an effort to save time and labor. It was also viewed as safer for the aircraft since it greatly reduced the number of contact points. McDonnell Douglas was aware of this practice, though they advised against it, referring to their own recommended method.

American Airlines—as well as Continental—utilized a forklift for removing, supporting, and reattaching the engine/pylon combination, an inaccurate means for supporting and aligning the heavy item. The pylon was observed making repeated, unwanted contact with the wing and the mounting points.

Believing they had found to cause of pylon’s damage, the NTSB examined all DC-10s belonging to the three airlines. Those belonging to United—who used an overhead crane for removal and reattachment—were found to have no pylon damage while fleets belonging to American and Continental turned up several units with damage matching that of Flight 191.

They had determined why the engine came off, by why had the plane come down?

A Lack of Information

As the investigation progressed, it was determined that approximately 3 feet of the left wing’s leading edge had been ripped away, damaging the aircraft’s hydraulic systems. As hydraulic fluid began streaming out, the force of the wing against the front of the wing was adequate to force the slats into retracting. The slats on the right wing, which was not yet devoid of hydraulic fluid, remained extended, creating what is known as a slat disagreement.

This is a serious issue since it leads to uneven lift and will force the aircraft to roll towards the side creating less lift. As such, there is a slat disagreement alarm. That said, why didn’t the crew react to it?

They never got it. That warning system on the DC-10 was powered by the #1 engine.

Then there’s the reduction of speed initiated by First Officer Dillard, which—when combined with the imbalanced slats—let to an asymmetrical stall. The crew was also unaware of this development since the plane’s built-in warning system—a stick shaker on the captain’s yolk—was also powered by the #1 engine.

A stick shaker for the first officer was available, though American Airlines did not equip this option on their DC-10 fleet. With this knowledge, we can see that the flight crew had little chance because the systems that would make them fully aware of their situation were either inoperable or not equipped.

Had they been aware of these issues and maintained a higher airspeed, the accident may not have happened. Then again, with the damage done to the wing (including damage to the hydraulic, electrical, and fuel systems) there’s the possibility that, even if the plane had continued climbing, a fire or explosion would have occurred.

At the end of the day, the flight crew did what they could with the information that they had and cannot be judged for not acting on information that was unavailable to them.

Legacy

While the tragic loss of American Airlines Flight 191 was not caused by a fault with the plane itself, the public’s perception of the DC-10 took a massive hit. Photographs of the stricken plane banking onto its side before crashing left an enormous mark on the psyche of air travelers.

The maintenance method which led to the pylon damage was banned and the FAA stated that any aircraft that underwent service in this manner would immediately be deemed unairworthy.

Ultimately, the DC-10 returned to service and today is still used by a handful of cargo carriers. The model’s last commercial passenger flight occurred in February of 2014.

Sadly, the crash of American Airlines Flight 191 had one more life to claim.

On March 25, 1981, Earl Marshall was found dead in his home, having committed suicide. Marshall had worked as crew chief at the American Airlines’ facility at which it is believed the fatal engine service was carried out. Marshall—who did not work on the ill-fated aircraft—was about to give a deposition on the crash of Flight 191.

In late 2011, a memorial for the victims of American Airlines Flight 191 was established and a special ceremony was held there to commemorate the 40th anniversary of the crash.

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