What happened
On 10 April 2010, a pilot was operating a private flight in an Avid Speedwing Mk 4 Flyer, registration G-LORT, near Bodmin. While cruising at approximately 1,900 feet, the pilot observed the engine coolant temperature gauge rising rapidly toward the vertical position. In an attempt to manage the temperature, the pilot reduced engine speed from 5,100 to 4,000 rpm. However, after roughly 15 seconds, the engine and propeller stopped abruptly without any prior signs of rough running.
Seeking a safe area, the pilot diverted to a field at Holne, Newton Abbot. As the aircraft approached the intended landing site, the pilot attempted to clear a hedge at the southern end of the field. The aircraft stalled at an altitude of approximately 15 feet, striking the ground hard just short of the field. The impact caused the main landing gear to collapse and the forward fuselage to buckle. The pilot sustained serious injuries, including a broken forearm and facial fractures.
The investigation
The AAIB investigation focused on the engine's mechanical state and the cooling system. Examination of the Rotax 582 engine revealed that the piston in the 'power takeoff' cylinder had significant scoring marks on opposing sides of the cylinder walls. This damage was consistent with a piston seizure caused by extreme overheating. The aft cylinder remained undamaged, and there was no evidence of detonation or lubrication failure.
Regarding the cooling system, investigators found that the coolant level in the overflow bottle was below the required minimum. While the radiator installation followed the aircraft's build manual, it differed from the standard Rotax installation, featuring a dual-radiator setup with a smaller expansion chamber. This configuration likely made the system less tolerant of coolant loss. Additionally, testing revealed that the temperature gauge was under-reading by approximately 40°F to 60°F, meaning the actual temperature was significantly higher than what the pilot observed on the instrument.
Findings
- The engine seized in flight because of overheating.
- The overheating was likely caused by a loss of radiator coolant from an unidentified leak.
- The temperature gauge was under-reading, which prevented the pilot from identifying the temperature excursion before the engine failed.
- The pilot's lack of recent flying experience on this specific aircraft type may have contributed to the outcome.