What happened
On 25 July 2004, a single-seat Pulsar kitplane, registration G-MCMS, was conducting a private cross-country flight from Perth to Oban. While cruising at 4,000 feet, the pilot noticed a burning smell. Shortly after, the engine failed to respond to throttle advances. The pilot attempted to declare a MAYDAY, but the radio operator was unable to understand the transmission.
Unable to reach Oban due to strong westerly winds, the pilot identified a flat field near a river for an emergency landing. As the aircraft descended to approximately 1,000 feet, the engine seized. The subsequent touchdown in the rough field was heavy, causing the landing gear to separate from the fuselage. The pilot sustained one serious injury (a crushed vertebra) but was able to exit the aircraft via the canopy and call for emergency services.
The investigation
Investigators examined the Rotax 582 engine and found that all coolant had drained from the radiators. A specific failure was identified at the port radiator's outboard hose coupling, which had detached. Metallurgical analysis of the radiator and coupling revealed that the failure occurred within the brass material of the radiator itself rather than at the brazed joint.
Microscopic examination suggested a progressive failure. While conclusive evidence of the exact mechanism was unavailable, the presence of solder contamination suggested the possibility of a previous repair or local overheating. Furthermore, the investigation found that the hose connecting the engine to the failed coupling was a straight piece of hose that had been bent into position, rather than the recommended curved or two-piece configuration.
Findings
- The engine overheated and seized following the loss of coolant through a failure in the radiator coupling.
- The radiator failure was likely caused by fatigue crack growth within the brass material.
- The use of a straight hose instead of a moulded or two-piece hose applied side loads to the coupling.
- Engine vibrations, characteristic of the Rotax 582, likely contributed to the propagation of the fatigue crack.
- The presence of heavy solder deposits indicated a potential undocumented repair or significant local heat exposure.