Finnish investigators have disclosed that a Finnair Airbus A320 descended far below the glidepath to Helsinki after the first officer unintentionally selected flaps-up instead of full-flap on approach.
The aircraft had been approaching Helsinki Vantaa airport's Runway 22L following a service from Budapest on 21 May.
The Accident Investigation Board of Finland says the captain requested full flap, but instead the first officer selected the flaps-up position.
The aircraft's speed, as a result, was 14kt (26km/h) below the minimum required for the configuration.
While the first officer realised the error within a short time, the aircraft descended 600ft (185m) during the incident when, under normal circumstances, it should only have descended 250ft.
The inquiry report from the accident board states that, during the recovery, the twinjet sank "considerably below the glidepath", to a height of 635ft above the ground.
Its crew aborted the approach and landed without further incident a few minutes later.
Investigators subsequently advised Finnair to double the minimum height for stabilising visual approaches, from 500ft to 1,000ft.