B738, vicinity Kittilä, Finland 2012

B738, vicinity Kittilä, Finland 2012

Summary

On 26 December 2012, a Boeing 737-800 experienced an uncommanded pitch up in IMC when intercepting the ILS GS at Kittilä. Initial crew response could not prevent a rapid transition to a very high nose up attitude and stick shaker activation occurred. Recovery from this upset was eventually achieved. The Investigation found that frozen de icing fluid had prevented three of the four input cranks for both elevator PCUs from functioning normally. It also concluded that, notwithstanding new de-icing procedures introduced by Boeing since the occurrence, the current aircraft type certification for all 737 variants may be unsound.

Description

On 26 December 2012 the crew a Boeing 737-800 (LN-DYM) being operated by Norwegian Air Shuttle on a scheduled domestic passenger flight from Helsinki to Kittilä as NAX 5630 temporarily lost control of the aircraft when a sudden, rapid and severe uncommanded pitch up occurred as the destination Instrument Landing System (ILS) GS was intercepted in day Instrument Meteorological Conditions (IMC) with the AP engaged. Upset recovery from stick shaker activation was achieved and there was no recurrence prior to completion of a second approach to land. None of the 179 occupants was injured.

Investigation

An Investigation was delegated by the State of Occurrence to Norway as State of the Operator and so the Accident Investigation Board Norway (AIBN) carried out and completed the work. DFDR data was successfully downloaded to assist the Investigation. However, the 2 hour Cockpit Voice Recorder (CVR) recording relevant to the occurrence was overwritten which almost eliminated any opportunity to examine Crew Resource Management. Recorded radar data covering the occurrence was also available.

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