Incident Overview
On Saturday, 20 January 2024, around 1000 hrs local time, an Aquila AT01-100, registration LN-NRC, suffered an engine failure shortly after takeoff from Kjeller Airport (ENKJ) in Norway. The pilot, the sole occupant, was conducting a private local flight. The aircraft had departed runway 30 at 0955 hrs. Approximately 1.1 NM from the runway threshold, over the Nitelva river, the pilot noticed a slight reduction in engine RPM from about 2,300 to 2,150, followed by a "clunck" sound and the propeller stopping. The altitude indicator showed about 600 ft (approximately 250 ft above terrain). The pilot activated the ELT, made a Mayday call on Kjeller Traffic frequency 119.100 MHz, and initiated a left turn toward a snow-covered field at Skjetten, a known suitable emergency landing site. The emergency landing was performed as normally as possible; the deceleration caused the nose wheel leg to fracture. The pilot shut off power and fuel, evacuated, and notified emergency services.
Aircraft and Engine Information
The Aquila AT01-100 is a two-seat, low-wing, composite aircraft with a maximum take-off weight of 750 kg. It is powered by a Rotax 912 S3 four-cylinder engine driving an MT-Propeller MTV-21-A/170-05 variable-pitch propeller. LN-NRC was imported to Norway in March 2018 and had a valid Airworthiness Review Certificate until April 2024. At the time of the incident, the aircraft had flown 71.5 hours since its last 200-hour inspection. The NSIA estimated the aircraft's mass and balance were within limits.
Engine Inspection
The NSIA removed the engine on 6 February 2024 and shipped it to BRP-Rotax GmbH & Co KG in Austria for inspection. On 7 May 2024, the NSIA and Austrian investigators examined the engine visually and through disassembly. They found that connecting rod #3 had punctured the crankcase, and the big end bearings of connecting rods #2 and #3 had failed with clear heat damage. The oil pump and filter showed no particles or damage, and the oil system lines were clear of blockages. The oil tank was completely full (approximately 3 liters), within the normal range of 2.55–3 liters.
Oil System and Cold Weather Considerations
The Rotax 912 S3 uses a dry sump lubrication system. The aircraft did not have an oil thermostat installed, which is recommended by the engine manufacturer for low ambient temperatures. The installation manual warns that the oil pump may not have adequate flow when the oil is cold. The ambient temperature at the time was approximately -24 °C, as reported by the pilot. The aircraft used SHELL AeroShell Oil Sport Plus 4 (10W-40), which the aircraft flight manual permits down to -25 °C, while the engine manufacturer specifies a lower limit of -20 °C for that viscosity. The engine manufacturer's service instruction later added a 5W-50 oil recommendation for improved cold-weather performance.
Outcome
The pilot sustained minor injuries. The aircraft sustained a fractured nose wheel leg and minor frontal damage; the engine was destroyed. No other damage occurred.