What happened
On 11 March 2019, a Tecnam P2002-JF, registration EI-GIS, was performing solo circuit training at Waterford Airport. During the pre-flight inspection, the student pilot noted that the engine coolant level in the overflow bottle was below the minimum mark, which was subsequently topped up by an instructor.
As the aircraft progressed through its flight pattern, the pilot noticed liquid dripping onto his left foot during the crosswind leg. Upon turning onto the base leg and reducing engine RPM, the aircraft experienced intense vibration and a significant loss of power. The engine failed to respond to throttle inputs, prompting the pilot to declare a Mayday. Realizing the runway could not be reached, the pilot attempted a forced landing in a nearby field. The aircraft touched down at high speed, bounced, and traveled through a boundary hedge. During the maneuver, the right wing struck a tree, causing the aircraft to roll and come to rest inverted. The pilot escaped the wreckage without injury.
The investigation
Investigators examined the engine and the aircraft's maintenance history to determine the cause of the power loss. The investigation focused on the coolant system and the fuel/air induction system.
Testing revealed that a pressure relief valve spring in the coolant expansion tank had failed, causing coolant to vent into the overflow bottle at low pressures. This led to an accumulation of excess coolant. Furthermore, investigators discovered that a coolant return hose for the third cylinder was not properly secured by its spring-band clamp. This lack of security was likely a long-standing issue dating back to a hose replacement in 2016, as evidenced by corrosion marks near the leak site.
Findings
- The primary cause of the engine failure was coolant ingestion into the engine cylinders.
- An unsecured coolant return hose detached due to back-pressure in the system.
- An unblanked tapping in the right intake manifold provided a direct path for the escaping coolant to enter the engine.
- The failure of the pressure relief valve spring caused the overflow bottle to overfill.
- The high-speed touchdown and subsequent impact with a tree were exacerbated by residual engine power and the use of take-off flap settings during the landing.
- The incorrect positioning of the hose clamp was difficult to detect because the area was obscured by fuel lines and ignition leads.