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A military drone crash report finds the craft’s maker as responsible for the failure. A British Army Watchkeeper drone crashed into the sea in February 2017 on a bad weather flight test, military investigators have said. The unmanned aircraft was trialling a new ice detection system. The UK MoD has 50 Watchkeepers remaining on charge.

The Watchkeeper (WK450) is an unmanned aerial vehicle (UAV) for all weather, intelligence, surveillance, target acquisition, and reconnaissance (ISTAR) use by the British Army.

Its endurance is over 16hrs from a single aircraft and 24/7 from a complete system. Its rapid deployment options enable operation within 2hrs and no support infrastructure. This multi-payload platform delivers an all-weather intelligence gathering capability, according to Thales website.

Investigators concluded that one of its pitot probes used for reading the aircraft’s speed and angle of attack (AOA) became blocked, causing the Watchkeeper’s onboard flight control logic to enter an erratic series of climbs and dives until it stalled itself and flopped into the sea.

The report criticizes the drone maker, Thales, for not fully understanding how its algorithms responded to loss of accurate sensor data, according to theregister.co.uk. Consequently, the effectiveness of the algorithms at maintaining the integrity of the air data required by the [flight control system] for safe flight was in part unknown.


So far the British military has crashed five Watchkeepers, including two in quick succession during 2017, which led to a months-long grounding of the entire fleet.

The automated decision-making that led to the crash has some parallels with the recent Boeing 737 Max controversy, in which automated flight control software has been fingered as a potential factor in two fatal airliner crashes that cost hundreds of lives.

A buildup of moisture in the Watchkeeper’s pilot probes was found to have caused its automated flight logic to start doing crazy things – ultimately leading to a stall and a crash.

Watchkeeper is not flown like a conventional aeroplane with a human sitting at a stick and rudder. Its operators select waypoints on a screen for the drone to fly itself towards. During flight, its onboard logic decides precisely how the drone arrives at those waypoints, within constraints selected by human operators.