What happened
While flying approximately 11.4 NM from Canberra Airport, the pilot noticed engine oil pressure levels dropping below normal. Although the aircraft's operating handbook advised a precautionary landing at the nearest suitable airfield, the pilot did not immediately decide to divert. This delay was driven by a misinterpretation of the pressure drop as being related to flight characteristics, as well as a reluctance to navigate the complexities of controlled airspace while far from Canberra. During this period, the pilot also experienced increased workload and fatigue due to hand-flying the aircraft through turbulence.
Once the decision to divert was finally made, the pilot initiated a powered descent toward Tumut Aerodrome. However, the engine failed approximately 5 NM from the aerodrome. Because the descent had already begun, the aircraft lacked the necessary altitude to reach the runway, resulting in a forced landing in a field.
The investigation
Investigators examined the engine and found a significantly low oil level, with oil coating various components and no oil present on the dipstick. While the decline in pressure matched the flight data, the source of the oil loss remained unidentified, as the oil cap was secure and the oil cooler showed no defects. The investigation also analyzed flight data, which suggested that if the pilot had diverted to Canberra immediately, a safe precautionary landing would have been possible. Furthermore, maintaining altitude until closer to Tumut would have likely provided sufficient glide range to reach the runway after the failure.
Findings
- The pilot's delayed decision to divert prevented a safe precautionary landing at Canberra Airport.
- Initiating a powered descent toward Tumut reduced the aircraft's glide potential, turning a precautionary landing into a forced landing.
- The specific cause of the engine oil loss could not be determined.