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Comment by kijin | Hacker News Reader

A speed of 9.81m/s is not free fall. Acceleration of 9.81m/s² is. If you're actually in free fall, you will quickly accelerate past 9.81m/s to whatever your terminal velocity is.

A typical passenger jet flies at a speed of somewhere between 100m/s and 300m/s. Just a small downward angle can add a vertical component to that vector well above 9.81m/s. That's what I think we're seeing here, not a plane dropping out of the sky.

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> A typical passenger jet flies at a speed of somewhere between 100m/s and 300m/s. Just a small downward angle can add a vertical component to that vector well above 9.81m/s. That's what I think we're seeing here, not a plane dropping out of the sky.

Don't pick on the commenter's unit mistake. The source material says "the aircraft would have dropped 1425 feet in 12 seconds maximum which requires about free fall acceleration" -- this is a 36 m/s descent; it started from a climb, and then ended in returning to 0 m/s at the minimum altitude. It's 2/3rds of a g acceleration downwards, minimum, if the data is valid.

Yeah - I think if it was an autopilot engagement, the velocity may have been gradual enough that it just felt a little weird. Add in clouds - it’s not a crazy amount of altitude to lose in a jet like this, and you prepare for some weird feelings getting on a jet in the first place.

Did the pilots just not look at the altimeter? I’m not a pilot but it seems to me once the autopilot is set you’d naturally look at the altimeter and maybe airspeed indicator to confirm it was working.

Altimeter is a secondary instrument for a climb. The primary instrument for pitch would be the airspeed indicator (for a typical constant speed climb). The fact that they noticed the descent (on the VSI and altimeter) and corrected indicates they were scanning, but doesn't tell much about what was happening that caused them to transition from a climb to descent.

Yeah, agreed here - workload on a departure (depending on the type of departure) can be pretty heavy compared to cruise phase. Arrivals and approaches are more commonly known to have heavy workloads, but there’s a lot to do just after departure, so this doesn’t feel wildly out of bounds for a scan recovery after an autopilot mistake.

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