Boeing 737-800 Near-Stall During Approach to Kittilä Airport (LN-DYM)

Incident Overview On 26 December 2012, Norwegian Air Shuttle ASA flight NAX5630, a Boeing 737-800 NG registered LN-DYM, was operating from Helsinki Vantaa Airport (EFHK) to Kittilä Airport (EFKT) in Finland. During the ILS approach to runway 34, the aircraft experienced an abnormal nose-up pitch and approached a stall. The Accident Investigation Board Norway (AIBN) issued its report in March 2015. ## Flight and Approach The aircraft had been parked outdoors for three days before the flight, during which approximately 25 cm of snow accumulated. Before departure, the aircraft underwent de-icing, with close to 3,000 litres of de-icing fluid used. The flight departed on schedule and proceeded normally until the approach phase. During the approach, the aircraft was established on the localizer at 4,421 ft AMSL with flaps 5, and both the autopilot and autothrottle were engaged. While intercepting the glide slope, the elevator trim began pitching the nose up. This condition continued for 12 seconds, during which the aircraft unintentionally climbed and the autothrottle commanded full engine thrust. ## Aircraft Response Both pilots applied full force to the elevator control column, but the nose continued to pitch up to an angle of +38.5° before slowly decreasing. The aircraft's speed dropped to 118 kt CAS, and the angle of attack reached approximately 25°, bringing the aircraft close to a stall. The autopilot disengaged just after the nose angle peaked, and control was gradually regained. A subsequent approach was completed without further issues. ## Investigation Findings The AIBN determined that de-icing fluid had entered the tail section and frozen on three or four of the input cranks for the aircraft's two elevator Power Control Units (PCUs), preventing them from functioning as intended. The investigation noted that even after the introduction of new de-icing procedures from Boeing, significant amounts of fluid and humidity continued to enter the Tail Cone Compartment during de-icing. The AIBN questioned whether this condition satisfied the certification requirements for the aircraft type and identified a need for measures to prevent ice formation on the input cranks, thereby reducing the risk of blocking normal elevator function on the Boeing 737 series. ## Safety Recommendations The investigation also identified potential improvements in the registration of inquiries received by the company's maintenance management center and noted that LN-DYM continued to operate after the incident. Three safety recommendations were proposed in connection with the report.