Investigation Summary
During the approach to Miami, the crew noticed the nose gear 'down and locked' green light failed to illuminate. While troubleshooting, the Captain accidentally applied pressure to the control column, which disengaged the altitude hold mode of the autopilot. The aircraft began a slow, unnoticed descent while the entire three-man flight crew and a jumpseat occupant focused on the light bulb and the manual gear extension viewing port. The C-chord altitude alert sounded at the engineer's station, but went unacknowledged in the distracted cockpit.
Final Conclusions
The NTSB determined the probable cause was the failure of the flight crew to monitor the flight instruments during the final four minutes of flight and to detect an unexpected descent soon enough to prevent impact with the ground. Preoccupation with a malfunction of the nose landing gear position indicating system distracted the crew from their primary responsibility of monitoring the aircraft's altitude.
Video Analysis
The Ghost of Flight 401 | The Tragic Story of Eastern Air Lines Flight 401 — A detailed look at how a simple $12 light bulb led to the first crash of a wide-body aircraft in the United States.
Watch on YouTube ↗If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
Autopilot Altitude Hold
The system maintaining the 2,000ft cruise, which disengaged into a sub-mode when the Captain applied 15-20 lbs of pressure to the yoke.
Nose Gear Indicator
A dual-bulb light assembly that failed to show a green 'safe' indication, triggering the chain of events.
C-Chord Alert
An audible warning that sounded when the aircraft deviated 250 feet from its assigned altitude; it was heard on the CVR but ignored by the crew.
Interesting Facts
- 01The crash was the first hull loss of a wide-body jet in the United States.
- 02The nose gear was actually down and locked; only the indicator bulb had failed.
- 0375 passengers and crew survived the initial impact and subsequent night in the swamp.
- 04The L-1011 autopilot logic allowed one axis (pitch) to disengage while the other (roll) remained engaged without a prominent warning.
Safety Actions & Advisories
CRM Implementation
This accident was a primary catalyst for the development of Crew Resource Management (CRM) to ensure pilots prioritize flying the aircraft over troubleshooting.
Autopilot Logic Changes
Manufacturers revised autopilot interfaces to provide clearer indications when a mode is partially disengaged or overridden by manual input.