Synopsis
On 2 July 2022 at 0738 UTC, a Tekever AR3 unmanned aircraft system (UAS) experienced an engine stoppage during a Beyond Visual Line of Sight (BVLoS) flight over the English Channel. The aircraft descended under parachute into the sea and was subsequently recovered. Investigation identified a failure of the low pressure (LP) fuel pump, which led to an electrical short circuit that tripped its associated fuse. This fuse also supplied power to the high pressure (HP) fuel pump, causing both pumps to stop and starving the engine of fuel.
History of the Flight
The flight departed from a site near Dover at 0502 hrs in good weather. After completing preflight checks and engine tests with no defects, the aircraft proceeded to a maritime surveillance mission within Temporary Danger Area D098 over the English Channel. Two remote pilots monitored the aircraft. After approximately one hour and eleven minutes of flight, while loitering at 800 ft amsl, the engine rpm dropped to zero and the throttle command rose to 98%. Altitude began to decrease, and the pilots recognized an engine stoppage. The aircraft followed its programmed route until reaching 550 ft amsl, at which point the parachute activation emergency procedure triggered automatically. The aircraft descended under parachute into the sea within the danger area. No other vessels were reported nearby. The operator alerted the Coastguard, activated the Emergency Response Plan, and informed the CAA. A fisherman later recovered the floating aircraft and returned it to the operator.
Aircraft Information
The Tekever AR3 is a UAS manufactured and operated by the same company, with an operating range up to 60 km, endurance of 8–16 hours, and maximum takeoff weight of 23 kg. A real-time data link provided aircraft parameters and video feed to the remote pilots. The single piston engine received fuel from a HP system that pressurized fuel from a header tank, supplied by a LP system that transferred fuel from the main tank via a filter/strainer using a separate LP pump. Both pumps were controlled by the Engine Control Unit (ECU) and shared the same electrical fuse, meaning a fuse trip would stop both pumps.
Investigation Findings
The operator conducted an extensive investigation using telemetry and examination of the recovered aircraft. The aircraft, propeller, and engine components were in good condition aside from saltwater effects and minor recovery damage. Telemetry indicated an engine rpm response typical of fuel starvation. The only issue found in the fuel system was damage to internal components of the LP fuel pump; the cause of this damage remains unexplained. Recorded electrical parameters suggested the damage caused an electrical short circuit, expected to trip the shared fuse and cut power to the LP pump, also isolating the HP pump and leading to fuel starvation.
Safety Actions
The operator identified that the loss of the LP fuel pump, fuse triggering, and internal pump failure were design issues that could lead to fuel starvation. Consequently, they implemented design improvements: a modification allowing the HP pump to draw fuel into the header tank if the LP pump fails; separate electrical fuses for the LP and HP fuel pumps; and use of an upgraded LP fuel pump. The CAA was informed of the investigation and modifications.