B1/2003L Accident of Cessna 172N at Pertunmaa on 23 February 2003

On Sunday 23.2.2003 at about 14.15 local time there was an aircraft accident at Pertunmaa in which a Cessna 172N aircraft, registered OH-CAX and owned by Mikkelin Moottorilentäjät ry, crashed on the ice of Lake Peruvesi. The pilot and two passengers were fatally injured and the aircraft completely destroyed by the impact forces. The Accident Investigation Board Finland decided on 24.2.2003 to appoint an investigation commission (number B 1/2003 L) to investigate the accident. Investigator Esko Lähteenmäki was appointed investigator-in-charge and investigators Juhani Hipeli and Ville Hämäläinen members of the commission. The commission used aviation medical doctor, Licentiate in Medicine, Eero Vapaavuori as an aviation physiology expert.

The take off was from a runway ploughed on the ice of Lake Ylä-Rieveli at Pertunmaa where the aircraft was meant to land as well. The flight began along the highway 5 to east-northeast towards the south end of Lake Peruvesi. The flight continued towards north above the lake at a height of approximately 150 m. The aircraft was seen to turn left and descend south of Hintosaari. The descent was steeper than normal and probably combined with reducing of the engine power. The descent was levelled off at a height of approximately 40 m and engine power was increased. At the end of the descent or immediately after that the aircraft turned right approximately back to its original heading. After this the aircraft began a steep straight or right turning climb and flied into a cloud. The pilot lost his spatial orientation in the cloud and lost control of the aircraft. According to the eye-witness’ accounts the aircraft was inside the cloud approximately 10-15 seconds after which is crashed on the ice of Lake Peruvesi almost vertically.

The aircraft was destroyed by the impact forces but all peripheral parts were found at the accident site. The aircraft had not disintegrated in flight. The flight control systems were functional during flight. A small amount of aluminium chips had been detected in the oil filter during two previous maintenance sessions. The chips were from two pistons and their pin plugs. The origin of the chips had not been located nor repaired. The chipping had progressed to such an extent that the oil filter had clogged and non-filtered oil circulated the system. The camshaft and valve followers had been considerably worn. Even though there was serious wear damage to the engine, the damage did not affect running of the engine. It was running at the time of the impact. The investigation commission discovered no evidence of any technical malfunction prior to the impact.

The cause of the accident was the loss of pilot’s spatial orientation and control after flying into a cloud unintentionally. Contributing factors were the fact that the aircraft entered the cloud in a steep straight or right turning climb and the fact that the pilot lacked proper instrument flying skill and touch. The investigation commission considers it probable that the pilot flew unintentionally to the cloud which was below the cloud base as he was demonstrating aircraft manoeuvring to the passenger seated beside him.

The investigation commission recommends that the flight instructors would emphasise in their training the fact that the attitude instrument flying training does not provide a real ability to control the aircraft in instrument flying conditions, and that it is only designed to provide an ability to perform a slow 180 degree level turn back. The commission also recommends that the maintenance personnel would locate the origin and perform corrective action before next flight even if a small amount of metal chips is found in the oil filter.

B1/2003L Report (pdf, 0.99 Mt)