Drone Manufacturer: DJI
Drone Model: Phantom 4 Pro
Country: United Kingdom of Great Britain and Northern Ireland
Pilot Qualifications: Approved by Public Safety Agency or Company
Pilot Flight Experience: 25 Hours
Link to External Information About This submission: https://www.gov.uk/aaib-reports/aaib-investigation-to-dji-phantom-4-pro-uas-registration-n-a
File Uploaded: dji_phantom_4_pro_uas_0519
Synopsis While on a surveying task the pilot was unexpectedly presented with a ‘landing’ warning, followed by several other warnings, before the aircraft entered a hover. Despite several attempts the pilot was unable to take control. The aircraft subsequently descended, colliding with a building as it did so, and was extensively damaged.
History of the flight
The aircraft was being flown on a surveying task in a built-up area, for which the pilot had approval. It took off on its third flight of the day with the battery indicating 51% charge and 13 minutes and 17 seconds of flight time remaining. After an uneventful few minutes, the enunciated flight mode, on the aircraft’s controller, changed from ‘gps’ to ‘landing’ without any warning or input by the pilot. This was followed by the following messages also being displayed on the controller: ‘Obstacle sensing will be disabled when aircraft is landing. Fly with caution Aircraft is close to home point. Initiate return to home will now trigger Auto Landing
The aircraft then entered a hover. Despite several attempts by the pilot to take control of the aircraft, including selecting A [Attitude] Mode and selecting RTH [Return to Home], the aircraft continued to hover. The pilot then rebooted the manufacturer’s application on the monitor connected to the controller, but this had no effect. He then changed the monitor for a portable electronic device, but the aircraft continued to hover and not respond to any inputs. The pilot then reconnected the monitor and ‘landing’ continued to be displayed. Shortly thereafter, having flown for about 6 minutes and 30 seconds, while it was in a hover, when the battery was indicting 11% and 2 minutes and 51 seconds of flight time remaining, the aircraft started to descend. As it did, it made contact with the side of a building and fell 30 ft. It came to rest on a flat roof, sustaining extensive damage to the aircraft.
The aircraft was initially inspected by a UK repair agency, which concluded that it had experienced an “unknown behaviour”. The aircraft, without its battery, was then sent to the manufacturer for further analysis. They concluded the accident was due to a “critical low battery landing” but were unable to provide further information as to what may have caused the loss of control.
During 2018, there were several events to aircraft fitted with the manufacturer’s TB502 and TB553 batteries where they indicated incorrect power levels. This was resolved by a firmware update4 . The manufacturer commented that this accident was not related to this issue.
The pilot commented that he was not presented with any low battery warnings during the accident flight. He has subsequently recharged and used the accident battery several times, in a new aircraft, without event.
The manufacturer concluded that the accident was the result of the aircraft commencing an automatic landing when its battery was nearly depleted. This may have been the case once the battery had reached 11% of charge remaining and started to descend. However, the pilot did not receive a low battery level warning, as stated in the aircraft’s user manual.