Helicopter fuel cap damage

On returning from offshore, a helicopter was to be re-fuelled for overnight parking in accordance with the Aircraft Maintenance Manual. At this time, the fuel outer cap was found to be open and had caused significant surface damage to the left-hand fuel tank side panel aft of the pressure refuel connection by the way of surface pitting and scratches.

The fuel cap had been free to float in the airflow during the flight while remaining connected via the chain/lanyard. The damage created, whilst significant, would not have been sufficient to cause any flight threatening hazard.

The most probable cause being the cap was not secured properly on refuelling completion, resulting in detachment mid-flight from vibration. The detached cap then dislodged the cover plate resulting in the fuel cap dangling in airflow with the chain lanyard remaining intact. Under normal circumstances, pre-flight checks by flight crew should have identified this potential problem, however, such checks did not take place due to temporary restrictions relating to Covid-19.