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By Dan Sobczak
Editor's note: This content does not constitute flight instruction. Consult a certified flight instructor in your area for proper flight instruction.
More than 45 years ago a small light bulb became the catalyst of an accident chain that led to one of the deadliest crashes in the history of the United States at the time.
A small light bulb became a catalyst for a deadly commercial airliner accident in the Florida Everglades in 1972. The lesson learned from this aviation accident has implications for every pilot, regardless of experience.
A Lockheed 1011 jumbo jet was on a regularly scheduled flight from John F. Kennedy International Airport in New York. The jet was on approach to land at Miami International Airport in Florida on a dark December night when it crashed into the Florida Everglades, killing 101 people.
The accident was puzzling because the passenger jet would have been able to land safely at its destination 20 miles away. All critical aircraft parts and systems were operating normally.
With that background, let's look at the accident chain of Eastern Air Lines Flight 401 from December 29, 1972, which started when the aircraft began its approach into Miami International Airport.
The text in the following accident chain outline contains excerpts from this Wikipedia article, which sources its information from the NTSB's final report (emphasis added is our own):
On Final Approach:
After lowering the landing gear, the First Officer noticed that the nose gear indicator light failed to illuminate. The pilots cycled the landing gear, but still failed to get the confirmation light. The landing gear could have been manually lowered.
Crew Begins Troubleshooting:
The flight crew told tower they wanted to discontinue their landing approach and requested to enter a holding pattern so they could troubleshoot the landing gear problem.
The approach controller cleared the flight to climb to 2,000 feet, and then hold west over the Everglades. The flight crew removed the light assembly.
The Second Officer was dispatched to the avionics bay beneath the flight deck to confirm via a small porthole if the landing gear was indeed down.
After reaching their assigned altitude of 2,000 feet, the flight crew put the aircraft on autopilot to maintain their assigned altitude, where the plane maintained level flight for the next 80 seconds.
80 Seconds Later:
After the L-1011 maintained level flight for 80 seconds, the aircraft dropped 100 feet of altitude, then flew in level flight for another 120 seconds. At this point, the L-1011 began a gradual descent which was not noticed by the flight crew.
The autopilot had been inadvertently switched from altitude hold to control wheel steering (CWS) mode in pitch. In this mode, once the pilot releases pressure on the yoke, the autopilot maintains the pitch attitude selected by the pilot until the yoke is moved again.
Investigators believe the autopilot switched modes when the Captain accidentally leaned against the yoke while turning to speak to the flight engineer, who was sitting behind and to the right of him. The slight forward pressure on the stick would have caused the aircraft to enter a slow descent, maintained by the CWS system.
Over The Next 70 Seconds:
The aircraft lost 250 feet of altitude, which was enough to trigger the altitude warning sound under the engineer's workstation. However, the flight engineer had gone below, and no indication was heard from the crew's voices recorded on the cockpit voice recorder that they heard the altitude warning.
Investigators believe this was due to the flight crew being distracted by the nose gear light, and because the flight engineer was not in his seat when it sounded.
As it was night time and the aircraft was flying over the darkened terrain of the Everglades, no ground lights or other visual clues indicated the aircraft was slowly descending.
50 Seconds Later:
The aircraft was now at half of its assigned altitude, at which point the First Officer noticed the altitude discrepancy. The following conversation was later recovered from the cockpit voice recorder:
First Officer: "We did something to the altitude."
First Officer: "We're still at 2,000 feet, right?"
Captain: "Hey -- what's happening here?"
10 Seconds Later:
Less than 10 seconds later, the aircraft crashed into the Everglades.
The final NTSB report cited the cause of the crash as pilot error, specifically:
"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's attention from the instruments and allowed the descent to go unnoticed."
The broken lightbulb wasn't the cause of the accident. Ultimately the crash occurred because the flight crew placed its focus on something that seemed to matter in the moment yet lost sight of the big picture.
That was a critical link in the accident chain.
This accident highlights how every pilot, regardless of experience, is at risk of making small mistakes that can lead to big problems.
The Flight Chain App team
Dan Sobczak is the founder of www.FlightChainApp.com, a mobile app that helps pilots learn from accident chains by making NTSB reports more convenient and easier to digest. Dan received his private pilot certificate in 2003.
Flight Chain App and its companion blog www.AheadOfThePowerCurve.com are committed to reducing general aviation accidents, helping improve aviation safety, and growing the pilot population.
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Flight Chain App and its blog Ahead of the Power Curve are committed to reducing general aviation accidents, helping improve aviation safety, and growing the pilot population.