What happened
During a local flight from Rivière-du-Luloup Airport, Quebec, an Amphibec advanced ultralight experienced a sudden engine failure shortly after takeoff. At approximately 1500 EDT, the aircraft was climbing at an altitude of roughly 200 feet when the engine stopped. Following the loss of power, the aircraft pitched upward, lost airspeed rapidly, and entered a steep left-hand turn and spin. The aircraft struck the snow-covered ground approximately 500 feet past the end of the runway. The two fatalities involved were the pilot and a passenger.
The investigation
Investigators examined the engine and cooling system to determine the cause of the power loss. The examination of the Rotax 582UL engine revealed that the rear piston had seized due to a loss of clearance between the piston and the cylinder wall. Evidence showed that the rear cylinder experienced much higher combustion temperatures than the front cylinder.
Technical analysis of the cooling system revealed that the bypass hose was not installed according to the manufacturer's diagram, and the aircraft was equipped with an oversized radiator. Furthermore, the engine was utilizing type 165 carburettor jets, which are intended for warm weather, rather than the type 175 jets recommended for cold operations. The investigation also noted that a defective crankshaft seal allowed air to enter the engine, thinning the air/fuel/oil mixture and contributing to the overheating of the rear cylinder.
Findings
- The engine stopped because the rear piston seized due to insufficient clearance.
- A defective crankshaft seal allowed air to leak into the engine, resulting in a leaner, hotter combustion mixture.
- The use of type 165 warm-weather carburettor jets in -14 °C temperatures caused increased thermal expansion of the piston.
- The cooling system was improperly installed and utilized an oversized radiator, which led to excessive cooling of the cylinder walls.
- The aircraft stalled at an altitude that was too low to allow for a successful recovery or emergency landing.