In a nutshell, while distracted, the crew fails to notice that they’ve nudged the flight stick and turned the autopilot off. And they are so distracted they don’t notice the chime that goes off to tell them they’ve moved to an altitude different than that of the autopilot.
I discovered there’s a 1978 made for TV movie with William Shatner covering the events. Excellent.
At no point in the program does anyone say, “They should have more than a GD ‘chime’. There should be an altimeter warning, a redundant warning after the autopilot is off, and something a little stronger than a ‘ding’.” ****ing ‘your lights are on’ warnings on cars are stronger.
I just don’t see how, even in 1972, anyone thought a single chime similar to the ‘fasten seatbelt’ heard for airplanes is enough for a situation like that.