The pilot of a Flybe plane that dropped 500ft (152m) in 18 seconds had selected the wrong autopilot setting shortly after take-off, an inquiry has found.
Some 44 passengers and four crew were on board the Belfast City to Glasgow flight on 11 January when the aircraft "pitched nose-down" towards the ground.
An Air Accidents Investigation Branch report said warnings alerted the pilot, who fixed the error at 928ft (283m).
Flybe said it had implemented "remedial actions quickly in response".
The report said that autopilot was engaged when the Bombardier Dash-8 Q400 turboprop plane reached an altitude of 1,350 ft.
The plane climbed to 1,500ft, but then pitched and "descended rapidly" because the autopilot was set with a target altitude of 0ft.
Staff reported that the plane "had become visual with the ground", and the report said the aircraft had reached a maximum rate of descent of 4,300ft/min.
The 60-year-old pilot "responded almost immediately" to cockpit alarms and disconnected the autopilot, the report found.
The flight continued as planned to Glasgow and landed without further incident.
The report said "several safety actions" had been taken by Flybe since the incident, including revisions to simulator training and amendments to the taxi checklist.
A statement from Flybe said the operator "maintains a rigorous approach to ensuring the very highest flying standards are maintained".
"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," it said.