Plane drops to 928 feet after autopilot set to 0 altitude

This is entirely caused because autopilot (Flight Management) systems are complex beasts with minimal feedback and sometimes very subtle interactions.<p>Ultimately the problem here was:<p>ALT mode was selected accidentally ALT SEL mode was selected later, but ALT mode wasn&#x27;t disengaged manually and engaging ALT SEL while in ALT mode doesn&#x27;t disengage ALT mode.<p>A combination of other factors (rushed during takeoff, interruptions from ATC, unfamiliarity with the Airport) caused the workload to be such that neither pilot picked up on the numerous subtle visual clues that showed that the autopilot was not going to do what they were expecting.<p>Luckily, after descending 500ft in about 18 seconds, audible warnings in the cockpit alerted the crew that things were going awry and they very quickly remedied the situation.

Reports like that are one of the reasons why I love aerospace. Where esle do people dive that deep into highly complex systems, no matter the time needed, to find the root cause. And come up with solutions afterwards. You can learn a lot system complexity, root cause analysis, human factors and a ton of other stuff from it.

Air Accidents Investigation Branch (AAIB) bulletin on this incident (it&#x27;s the first report on page 3). Posting mirrors first so we don&#x27;t crash a little gov site if this gets popular.<p>Low resolution mirror: <a href="https:&#x2F;&#x2F;drive.google.com&#x2F;file&#x2F;d&#x2F;1P7czQkX_9_e7fBDYaFWG0OlwtppgLh9R&#x2F;view?usp=drivesdk" rel="nofollow">https:&#x2F;&#x2F;drive.google.com&#x2F;file&#x2F;d&#x2F;1P7czQkX_9_e7fBDYaFWG0Olwtpp...</a><p>High resolution mirror: <a href="https:&#x2F;&#x2F;drive.google.com&#x2F;file&#x2F;d&#x2F;1ulgy8cGSrG7nT1_p6PmKlxTBBi_6yVLQ&#x2F;view?usp=drivesdk" rel="nofollow">https:&#x2F;&#x2F;drive.google.com&#x2F;file&#x2F;d&#x2F;1ulgy8cGSrG7nT1_p6PmKlxTBBi_...</a><p>Original links can be found at: <a href="https:&#x2F;&#x2F;www.gov.uk&#x2F;government&#x2F;publications&#x2F;air-accident-monthly-bulletin-november-2018" rel="nofollow">https:&#x2F;&#x2F;www.gov.uk&#x2F;government&#x2F;publications&#x2F;air-accident-mont...</a>

Question, why is 0 a valid entry for autopilot? Would that ever be used?

To be pedantic, the pilot, while on the ground, when setting (but before engaging) the autopilot selected a mode where the autopilot uses the current altitude (i.e. 0ft) as the target altitude. As mrunkel explains elsewhere, this never got corrected (due to crew work-load during take-off) before the plane reached the altitude where the pilot actually engaged the autopilot.<p>The pilot almost immediately did the right thing and disengaged the autopilot, recovered. They then re-engaged the autopilot and the same problem happened again (but with less loss of altitude). Only then did they set the autopilot correctly.<p>Similar incorrect settings had happened to three prior flights although in one of these the pilot spotted the problem before engaging the autopilot.

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&#x27;t notice for 15 seconds until an alarm went off, when the pilot immediately disengaged the autopilot, pulled up, and reduced engine power.

Is it common to set autopilot below 5,000 feet or so? Seems kind of like setting your cruise control at 25 MPH.

This shows the necessity of reasonable defaults. Not a pilot, but somehow I think the default setting for ALT should NOT be 0.

The system functioned as designed. The ground proximity alarm sounded and the pilot in command took control.<p>It&#x27;s possible the pilot should have refrained from engaging the autopilot during initial climbout. Pilot workload is high at that point in a flight, and fiddling with gadgets is distracting. Maybe wait until passing through 5,000 feet?

When I was learning to fly, one busy day my instructor and I were stuck waiting on a taxiway so he pulled up the autopilot and we had a play.<p>One of the preflight checks is that the autopilot is disengaged for takeoff, but we did this after the checklist.<p>We took off with the autopilot set to something like 4000ft, making it want to climb at an impossible rate of climb. As a novice pilot it took me several seconds of fighting the controls to figure out what had happened, all the while with the stall horn blaring on takeoff. Scary lesson.

I would think the pre take off checklist would include configuring autopilot for your planned departure altitude&#x2F;heading&#x2F;whatever.

Validation issue?