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Comment by PhasmaFelis | Hacker News Reader

The article makes it sound like the autopilot was engaged, the plane slammed into a dive, and the pilots panicked for 18 seconds before finding and fixing the problem. It looks like what actually happened is the plane started to slowly pitch down; the pilots were busy with the after-takeoff checklist and didn't notice for 15 seconds until an alarm went off, when the pilot immediately disengaged the autopilot, pulled up, and reduced engine power.

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"An Air Accidents Investigation Branch report said warnings alerted the pilot, who fixed the error at 928ft (283m)."

It's odd, you'd think that the sensation of dropping 500ft (152m) in 18 seconds would have alerted him, especially after take off. It's hard to visualise what that would feel like.

You are expecting some change in G-force due to changing to AP, you don't necessarily feel the start of the drop and once descent is consistent, it won't feel that alarming, add to that the fact that you think the AP is correctly set and you have confirmation bias and won't notice anything wrong.

Just goes to show that we still don't really know if we should "trust the plane" or "trust the pilot".

Regarding who to trust; both: trust the whole cyber-physical system. And like OP said, the system worked as designed. The bigger system now even learns from this and improves the existing cyber-physical system to handle such cases even better / earlier or avoid them: "Flybe implemented remedial actions quickly in response to the incident and our training and procedures have been amended to minimise the risk of a reoccurrence".

I mentioned this is another comment but

If you read the UK Government report that is not what happened. The plane was at 1500 ft when it began to descend. At 1300 ft the warning sounds activated and the pilot reacted but it took another 300 ft of descent before the pilot was able to fully recover from the descent.

Imagine being the flight attendant trying to pour coffee in what was probably a 1.5G (or thereabouts) maneuver.

The cabin crew is almost surely seated below the 10,000’ MSL level. (Many airlines give the cabin crew a chime signal to indicate they’re in the climb, high enough, and expecting it’s safe to begin cabin service. Below 10K, cabin crew is focused on safety not coffee service.)

In an ideal world this might be true. In practice below 10000ft the cabin crew are focused on grabbing some lunch, a drink or just a rest before the rest of the flight.

Source: My partner is ex-cabin crew.

Well, it does say they reached a descent rate of 4,200 ft/min (72 ft/second), which is pretty rapid.

you only feel acceleration not speed though - depends how quickly it accelerated to 22m/second - presumably linearly through the 18 seconds? which means 1.2m/s^2, or about 0.12G - not that extreme really

Yeah, it’s certainly not a freefall, but still scary. They pulled out of the descent at 928 feet, descending 72 feet per second. Assuming they were still accelerating, they were probably less than 10 seconds from the ground. Good thing the pilot reacted to the alarms immediately!

Of course, we don’t know if there were other systems to prevent this. But if there weren’t, and it was truly a situation of “if the pilot reacts 10 seconds slower here, everyone dies”, then they should likely put more sanity checks into the autopilot system.

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