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 (

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. 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. Similar incorrect settings had happened to three prior flights although in one of these the pilot spotted the problem before engaging the autopilot.