Serious incident to the De Havilland DH6 registered F-OCQZ operated by Aircalin occured on 04/05/21 at Futuna

Between 12 February and 4 May 2021 (the day of the event), four malfunctions relating to engine power problems on the ground had been observed and recorded in the Aircraft Technical Log (ATL). For all four events, the problems were not reproduced during the maintenance operations that followed.

The day before the event, the pilots had carried out a night training flight without noticing any power problems.

During the freight commercial air transport flight between Wallis and Futuna on 4 May 2021, the pilots decided to increase the approach speed by 10 kt due to possible turbulence. The speed range between the adopted speed and the Vmax was therefore reduced (by approximately 8 kt). The pilots were used to this speed increase, which was a strategy for adapting to the lack of reliable weather data and the absence of a windshear indicator in the aeroplane.

After momentarily reducing the power to idle to decrease speed, the PF noticed that the power did not come back up, and he did not hear the expected noise from the engines. The speed continued to drop despite his attempts to increase power and finally moving the levers up to the full power stop. He managed to land the aeroplane on the runway with a nose-down input and an early flare. The crew did not notice any thrust dissymmetry when increasing power.

Ground tests carried out by the crew confirmed the power problem on the RH engine (engine #2). The LH engine (engine #1) was not tested immediately, and the problem was not
subsequently confirmed.

The examinations carried out on the FCUs of both engines revealed an unusual level of contamination, made up of environmental elements and grease (probably engine oil), which may have caused malfunctions such as a lack of engine power increase, although this was not established with certainty.

The investigation was unable to determine with certainty the cause of this contamination.