Incident Overview
On 25 January 2019 at 10:10 local time, a Matternet M2 V9 unmanned aerial vehicle, registration SUI-9909, operated by an American national born 1985, experienced a technical problem during a commercial flight over Lake Zurich, Switzerland. The drone was transporting blood samples on behalf of Swiss Post. It departed from Klinik im Park in Zurich with a programmed route to Zentral Labor Zurich (ZLZ) near Balgrist. The flight was conducted under visual flight rules (VFR). The operator had 540 hours total flight time, with 40 hours 35 minutes on type within the preceding 90 days.
Flight Sequence
Before the first flight of the day, a test flight was performed with no anomalies. A sister drone of the same type had already flown to Unispital without incident. The operator received the packaged sample at Klinik im Park and completed pre-start checklists with the flight director (F/D) via conference call. The drone was launched at 10:09. It climbed vertically to approximately 60 m above ground level and reached a cruise speed of about 19 m/s (68 km/h) within 20 seconds.
At 10:10:05, a few seconds after crossing the western lake shore, the drone lost the GPS signal. It continued on the programmed route for a few seconds. At 10:10:10, unable to determine its position, the drone automatically initiated an emergency landing. The Flight Termination System (FTS) deployed a parachute, and the F/D in the mission control unit saw an alert reading "FTS fuse false." The F/D had no ability to influence the situation. The drone descended parabolically from about 60 m with an average vertical speed of 4 m/s, struck the water surface, and sank. The blood samples remained intact, and no persons were injured. Following the emergency plan, the F/D notified the police. The drone was recovered on 28 January 2019 from the lake bottom at a depth of approximately 20 m.
Investigation Findings
At start, the flight battery voltage was 47.86 V; at the initiation of the emergency landing, it was 48.24 V. When the drone submerged, seawater ingress caused a short circuit in the power electronics, battery management system, and the battery itself, discharging the battery. Upon recovery, the parachute's main line was found attached to the structure next to the parachute compartment, with a piece of the fairing broken off. No other external damage was observed.
Further investigation revealed that the 5 V supply to the GPS receiver and the precision landing sensor had failed. This power supply was routed through a modified ODU connector, the pins of which were positioned very close to one another. The main avionic board was coated with protective resin, but many connectors exhibited low environmental protection.
Aircraft Description
The Matternet M2 V9 (serial M2-0025, N705MN) was built in 2018. It is a quadcopter powered by four electric motors (XRotor PRO 6215 180KV) and a lithium-ion battery with a capacity of 756 Wh. Maximum takeoff weight is 13.2 kg, maximum payload is 2 kg, and maximum cruise speed is 20 m/s. It communicates via a GSM network and is approved for VFR operations day and night. The drone is equipped with a collision warning device (Flarm), anti-collision lights, and a parachute-based FTS that limits impact energy to approximately 90 J. The FTS deploys a parachute under spring tension, with an electronic fuse. When deployed, the drone descends at 3–5 m/s and emits a loud warning sound.
Probable Cause
The source did not provide a stated probable cause.