What happened
On 12 June 1998, a Robinson R2ly helicopter, registration G-OTYA, was conducting a private flight near Luton, Bedfordshire. During the cruise phase of the flight, the pilot observed that the fuel gauges indicated a critically low level in the aircraft's auxiliary fuel tank, even though the main tank appeared to be nearly full. Shortly after this observation, the auxiliary tank reached empty, causing the engine to misfire and subsequently lose power. The pilot performed an autorotation, which resulted in a heavy landing and substantial damage to the aircraft. No injuries were reported.
The investigation
Following the incident, investigators examined the fuel system and discovered that the vent for the left-hand main fuel tank had become blocked. This blockage was caused by a kink in the plastic tubing of the vent system. An inspection by an engineer revealed that the aircraft was not equipped with an intertank vent, meaning the tanks could not balance pressure through one another.
Further investigation into the vent system's history showed that the plastic tubing used in the assembly was susceptible to deformation. The tubing was located in an area subject to heat from the engine heat shield, which could soften the plastic and make it prone to kinking. While the UK agent had recently performed an annual inspection and installed an upgraded kit, the investigation found that the plastic pipes used in these systems often failed to maintain a consistent diameter.
Findings
- The engine failure was caused by the blockage of the main fuel tank vent due to a kink in the plastic tubing.
- The plastic tubing used in the vent system was vulnerable to kinking because it softened when exposed to heat from the engine heat shield.
- The aircraft lacked an intertank vent, which would have allowed the tanks to vent through each other.
- The existing vent system design, utilizing single-walled general-purpose plastic tubing, lacked sufficient resistance to deformation under operational heat levels.