Introduction
On 25 July 2004, at 1305 hours UTC, a Pulsar single-seat kitplane registered G-MCMS experienced an engine failure near Taynuilt, Scotland. The aircraft was on a private cross-country flight from Perth to Oban. The pilot, aged 52 and holding a Private Pilot's Licence, had 408 total flying hours, including 50 on type.
Flight History
While at 4,000 feet on the Oban QFE, the pilot detected a burning smell. Advancing the throttle did not produce an engine response. He declared a MAYDAY to Oban Radio, but the message was not understood by the radio operator. Due to strong westerly winds, the pilot determined he could not reach Oban and selected a field beside a river for a forced landing. At approximately 1,000 feet above ground level, the engine seized. The aircraft touched down hard on rough terrain with grazing cows at the eastern end. During the ground roll, the landing gear separated, and the aircraft decelerated rapidly. The pilot opened the canopy and vacated the aircraft, then called emergency services via mobile phone. He later was found to have a crushed vertebra.
Engine and Radiator Examination
The aircraft was powered by a Rotax 582 two-stroke liquid-cooled engine with two radiators mounted in the forward cowling. Following the accident, a Popular Flying Association inspector found that all coolant had drained from the radiators, with a small pool in the lower cowling. The port radiator's outboard hose coupling had detached from the radiator. The failed coupling, radiator, and hoses were sent for metallurgical examination.
Examination revealed that the failure occurred in the brass radiator material rather than at the brazed or soldered joints. Scanning electron microscopy showed that the fracture surface was largely contaminated, but a clean area at the upper left indicated final overload failure. The lower part of the fracture appeared to have been present longer, with signs of transgranular fracture and faint parallel markings possibly indicating fatigue striations. Solder contamination on the lower fracture surface raised the possibility of a prior repair attempt, though the aircraft logs showed no record of such repair.
The hose connecting the engine to the failed coupling was a straight hose that had been bent into position, whereas the construction manual specified either a curved moulded hose or a two-piece hose with a 45-degree intermediate fitting. This bent hose likely applied side loads to the coupling, potentially contributing to fatigue crack growth. Additionally, the brass connecting tube of the failed coupling was offset downward by approximately 5 degrees, which may have added to the loading.
Findings
The engine failed due to overheating following loss of radiator coolant. The coolant loss occurred through detachment of the port radiator outboard coupling, resulting from a progressive crack in the brass radiator, possibly induced by fatigue from side loads transmitted through incorrectly installed hoses. No similar failures were known to the Popular Flying Association or Pulsar Aircraft Corporation, though the pilot was aware of another Pulsar owner who experienced a leak at the radiator fitting.
Probable Cause
The engine failed because it overheated following a loss of radiator coolant.