Date: 29 December, 1972
Operator: Eastern Air Lines
Flight number: 401
Aircraft type: Lockheed L-1011 Tristar
Location: Florida Everglades, near Miami International Airport [MIA]
Fatalities: 101 of 176
Relevant weather conditions: Darkness
Accident type: controlled flight into terrain
Primary causes: Pilot error, poor Crew resource management.
The following is a human factors analysis of the crash of Eastern Air Lines Flight 401; factual information of the sequence of events is drawn primarily from information provided by the National Transportation Safety Board [NTSB] (19731).
Sequence of events
Flight 401 was approaching Miami International Airport at about 2330 local time, when the nose landing gear position indicating system light did not illuminate. The pilots had to identify whether the gear had indeed failed to extend, or more likely, that the bulb had simply burned out. As a result, the pilots aborted the landing and the first officer set the autopilot to keep the aircraft at 2000 ft to allow them to sort out the problem.
Autopilot mode switch
Shortly afterwards, during a discussion regarding the landing gear, the FDR detected slight nose-down pressure on the captain's control column. This coincided with the captain asking the second officer to check the gear through the avionics bay viewing window. It is likely he unknowingly bumped the control column while turning to speak with the second officer, enough for the pitch mode to swap from altitude hold to control wheel steering, which initiated a gradual descent.
Difficulty changing bulb
Meanwhile, the captain and first officer tried to replace the bulb and confirm that the original had indeed burned out. CVR recordings clearly revealed that the crew was frustrated with the problem of changing the bulb, as the cover had jammed.
Indications of descent
Due to differences in the two pitch computers, the first officer's display still indicated that the autopilot was in pitch mode. As the aircraft descended 250 ft below the assigned altitude of 2000 ft, an aural warning from the second officer's speaker was detected on the CVR, but the crew seemed to be unaware of it, and by that time the second officer was already in the avionics bay. There were at least four indications that the L-1011 was slowly descending towards the Everglades. The altimeter, vertical speed indicator, the captain's autopilot display, and the aural warning all went unnoticed by the crew.
Just a few minutes later, while the pilots were still working on the problem, the first officer noticed that the altimeter was indicating a dangerously low altitude, and then the radar altimeter sounded an altitude warning. However, by the time the pilots realised their situation it was too late; flight 401 impacted the Everglades in a left turn and began to disintegrate, the wreckage being strewn over an area of 50 square kilometres. It was the first accident involving a wide-bodied airliner, and the most deadly crash in the United States at that time.
Investigators were puzzled to subsequently discover that apart from one burned out bulb, there was nothing wrong with the L-1011. The main causal factor in this accident was not the aircraft, but the crew, the human factor.
Even though the crew was dealing with the landing gear indicator, they still could have noticed their surroundings and the aircraft's altitude. As long as stress levels are not too high, the average human has enough additional information processing capacity to notice things unrelated to the current task, such as the aural altitude warning, and instruments indicating a descent (Robson, 20082). When stress levels increase, however, it is possible for cognitive tunnelling to develop (Chou, Madhavan, & Funk, 19963); this is where one particular task is given a very high priority at the expense of other tasks. It can be especially dangerous when the task being focused on is actually less important than those tasks being neglected. Initially, it may seem that the crew was presented with the simple task of changing a lightbulb. However, as the cover had jammed, both the captain and first officer likely experienced cognitive tunnelling as they tried to establish a way of replacing the bulb without breaking the cover. In this case, all of their attention was given to this one small problem, at the expense of flying the aircraft.
Command/control & CRM
The fact that all three crew members were dealing with the problem in the first place was an extreme command/control failure. The most basic level of command/control is crew coordination, ensuring that individual tasks, such as replacing the bulb, and flying the plane, are effectively divided between crew members so that the main overall objective, in this case landing the aircraft safely, can be successfully accomplished (Kanki & Palmer, 19934). This was a deficiency on behalf of the captain to either delegate or take control of the landing gear, and have at least one pilot in charge of flying the plane. At the time, CRM was not a developed system and so the crew did not have the opportunity of developing the same effective team-work skills as modern pilots.
Errors committed by the crew were the main cause of the crash of Eastern Air Lines Flight 401; it was a landmark accident for more ways than one. The first crash of a widebody airliner provided a strong catalyst for the development of CRM systems, and has served as a strong example for the benefits of CRM training.