C4/2006L Engine failure and emergency landing at Joensuu airport on 24 March 2006

On Friday 24 March 2006, at approximately 17:10 local time, an incident occurred at Joensuu airport, when a Cessna 172P aircraft, owned by Tervalentäjät ry and equipped with a diesel engine, was damaged in an emergency landing. The pilot, who was alone in the aircraft, sustained only minor injuries.

On 4 April 2006 the Accident Investigation Board Finland (AIBF) appointed in its decision no. C 4/2006 L an investigation commission with Chief Air Accident Investigator Esko Lähteenmäki as investigator-in-charge and investigators Hans Tefke and Tuukka Takala as members of the commission.

Before the incident flight a 200 hour scheduled maintenance check and annual inspection was performed on the aircraft. As a part of the maintenance work, the oil pressure sensor was replaced. Replacing the sensor required either the removal of the flexible intake air tube located on top of the engine or at least opening of the tube attachment clamp at the front end (intake manifold end). The mechanic opened the front end attachment and changed the sensor. After doing this he proceeded to another aircraft and asked another mechanic to bind the sensor wires and reattach the open end of the tube. Whilst attaching the tube the second mechanic noticed tension forming in it, so he loosened the aft end attachment of the tube (the attachment is an ordinary worm-drive clamp). After assembly the aft tube attachment was left untightened. After completion of the work, the first mechanic visually checked the assembly, and the tube appeared to be correctly attached. A ground test run was performed on the engine and the aircraft was released to the pilot.

According to his account, the mechanic had performed an engine test-run using the FADEC test routine. The use of maximum power during the test run was brief due to the apron surface being so slippery that the aircraft did not hold still when maximum power was applied. The engine maintenance checklist state that maximum power should be applied for 30 seconds. According to the engine manufacturer, application of maximum power for the time specified is important and it enables the opening and the consequent detection of possible loose intake air tube attachments.

During takeoff, as the aircraft was climbing at an altitude of approximately 300 ft, the loose intake tube attachment opened completely, the flexible rubber tube was sucked in and blocked and the engine stopped instantly. The pilot performed an emergency landing into the front sector touching down into snow outside the runway area. During the flare the aircraft rolled over. The engine stopped during the initial climb after takeoff. The runway length remaining was insufficient for landing because the takeoff had been initiated from the runway midpoint. The engine stopped due to the opening of the intake tube attachment which had been left loose during maintenance. The loose attachment was not detected in the final inspection or during the engine ground test run.

The investigation commission made two safety recommendations. The commission recommended that the engine manufacturer and maintenance personnel should seal tube attachment clamps using paint marking or safety-wire, enabling an easy visual detection of opened attachments in the final maintenance inspection. The investigation commission also recommended that takeoffs with single-engine aircraft be performed using the entire takeoff distance available, from the departure end of the runway, even in cases where the minimum takeoff distance requirement indicated in the aircraft manual is less than the runway length available.

C4/2006L Report (pdf, 0.34 Mt)