On 29 December 1972, Eastern Air Lines flight 401 crashed into the Florida Everglades on approach to Miami. 101 of the 176 people aboard died. The aircraft was fully serviceable. The crew were experienced. The thing that killed them was a light bulb.
The sequence
On approach, the nose landing gear indicator light did not illuminate green. This meant either the gear was not down and locked, or the bulb had failed. The crew requested a hold and climbed to 2,000 feet over the Everglades to work the problem.
All three flight crew — captain, first officer and flight engineer — became involved in troubleshooting the indicator. The captain tried to extract the light assembly and it jammed. The flight engineer went into the electronics bay below to check the gear visually. Attention in the cockpit was entirely on a two-dollar component.
Somewhere in this, the autopilot was disengaged, probably by inadvertent pressure on the control column. The aircraft began a very gradual descent. An altitude alert chimed, and nobody responded to it. The Lockheed L-1011 flew into the swamp at night, in level flight, with everything working.
What the investigation established
The NTSB found the probable cause to be the crew's failure to monitor flight instruments during the final minutes, with preoccupation over a malfunctioning indicator as the distraction. It also noted that nobody had been assigned to fly the aircraft while the others worked the problem — the role of pilot flying had simply dissolved.
Why it matters
Eastern 401 is one of the founding cases of what became Crew Resource Management. Together with Tenerife five years later, it defined the two failure modes CRM addresses: at Tenerife, a junior crew member could not effectively challenge a senior one; here, an entire crew lost situational awareness together because nobody's job was to keep watching.
The practices that came out of it are now unremarkable. One pilot is explicitly designated to fly and does not participate in troubleshooting. Task-shedding is trained: when workload rises, the aircraft comes first and the problem waits. Altitude alerts are treated as mandatory callouts, not background noise.
Ground proximity warning systems, mandated across the US fleet a few years later, addressed the same class of accident from the technical side — controlled flight into terrain, where a working aircraft is flown into the ground by a crew who do not realise it.
The other story
Eastern 401 is also known for the widely circulated accounts of crew members from the crashed aircraft being seen aboard other L-1011s, on which a popular book was written. Eastern denied it, and the salvaged parts explanation has never been substantiated. It is worth separating it from the accident itself: the reason 401 is taught has nothing to do with that, and everything to do with the light bulb.