Doing so would allow the plane to pass through MDA and continue to descend while it leveled off. For example, it appears that the pilot attempted to level off only after he reached minimum descent altitude. The NTSB found a few points at which the pilot or first officer did not strictly adhere to landing procedures on approach to Tri-State Airport. The FDR data suggests that the pilot tried to do just that before striking the trees. This would require the airplane to level off and turn around. Shortly before the crash, he remarked, "Bet'll be a missed approach." Investigators believed that he noticed that the plane was approaching MDA but had not made visual contact with the airport.
The flight coordinator's duties required him to talk to the pilot, so he was allowed to be in the cockpit. The CVR also recorded a comment from the flight's charter coordinator, a Southern Airways employee who was in the cockpit just before the crash. Investigators did not believe that the pilot was using the autopilot incorrectly or that the autopilot caused the crash. The pilot also remarked that the autopilot seemed sluggish. It appeared to capture a glide slope signal even though the airport had no glide slope. The pilot and first officer did not note any cause for concern other than a minor issue with the autopilot. In addition, according to the conversations recorded by CVR, the crew believed the plane was on a normal descent to the airport. It is unclear whether the pilot verified the callouts on his own instruments or whether he relied on the first officer's readings. The first officer's callouts as recorded in the cockpit voice recorder (CVR) were consistently higher than the measurements recorded in the plane's FDR. Regardless of exactly why the plane was flying too low, the pilot and first officer were probably completely unaware that it was doing so. The NTSB investigators reported that the use of radio altimeters on approach to the airport was possible, but not probable.
The pilot and first officer would have known this from their training. But in very hilly or uneven terrain, like the area of West Virginia where the plane crashed, radio altimeters could give inaccurate readings. It measures the amount of time it takes for radio waves to travel to the ground and back. A radio altimeter works essentially the same way as radar. Another theory was that the pilot and first officer were using their radio altimeters to determine the plane's altitude.
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