On May 25th, 1979, American Airlines flight 191 crashed shortly after takeoff, killing all 271 people on board as well as two people on the ground. This was, and still remains, the deadliest single-aircraft aviation accident in US history. This followed fatal major disasters in 1972 and 1974 as well as several severe yet non-fatal incidents in the years leading up to flight 191. Days after the crash, the Federal Aviation Administration (FAA) grounded the DC-10 after inspections of other aircraft revealed serious safety concerns with the type.
Flight 191 investigation findings
In a “Lessons Learned” document covering Flight 191, the FAA states the following:
- The DC-10 experienced a left-wing engine/strut failure, and subsequent engine and strut separation.
- The left engine and strut assembly, and about three feet of the wing leading edge, separated from the wing as a single unit, and fell to the runway.
- The pylon separation also severed hydraulic lines, causing a loss of associated hydraulic pressure and retraction of all slats outboard of the left engine.
- Another outcome was the loss of electrical power provided by that engine’s electrical generator, resulting in the loss of many aircraft systems and instruments, including:
- Flight instruments,
- Left stall warning computer,
- Stall warning motor,
- Number 1 engine instruments,
- Slat disagree warning system,
- And parts of the flight control indicating system.
The US National Transportation Safety Board (NTSB) ruled that the accident was due to American’s decision to ignore McDonnell Douglas’ instructions during a maintenance procedure. This procedure required the removal of the engine and the pylon connecting it to the wing:
“Strut failure was determined to have been caused by unintended structural damage which occurred during engine/pylon reinstallation using a forklift…The NTSB concluded that the procedure had not been sufficiently evaluated, and appropriate consideration had not been given to the potential for inducing damage.” -FAA Lessons Learned
The video below (at 0:30) demonstrates what happened with Flight 191:
Subsequent DC-10 grounding
According to an article by Aviation Week & Space Technology, the grounding affected 138 US registered DC-10s as well as most foreign-registered aircraft. The FAA’s decision applied to countries “having bilateral agreements with the US covering aircraft certification.” Furthermore, those without bilateral agreements were banned from flying into any US airports or even using US airspace.
While foreign airlines were allowed to ferry their aircraft back to home maintenance bases, domestic airlines were not given the same immediate luxury. Instead, the FAA would eventually provide a procedure that would enable US carriers to ferry their DC-10s back to their maintenance bases.
In total, the DC-10 stayed grounded for 37 days.
What happened post-grounding?
Even though the DC-10 returned to the air in a relatively short manner of time, the accident was a wake-up call for the industry and regulators. The NTSB called for better tracking and reporting of maintenance-related damage, stricter oversight of maintenance, as well as tougher vetting when airlines look to deviate from manufacturer-endorsed methods.
As for aircraft-specific changes, airlines were ordered to inspect their DC-10s for damage and adhere to the manufacturer-endorsed maintenance procedure. The FAA also ordered improvements to the DC-10’s warning systems, revising flight manual procedures for handling an engine failure.
The FAA handed American and Continental fines of $500,000 and $100,000, respectively, for improper maintenance. Those numbers are about triple when converted into 2020 terms.
As one rather strange and unexpected outcome, an Illinois law now encourages that dentures be marked with information identifying the wearer. The forensic dentist working through the wreckage of flight 191 said he pushed for the measure after realizing it could have helped verify victims’ identities.