Alarm Messages
When did the event happen ?
August 2025
Drone
DJI Air Series
Level of experience
Intermediate
Environment
Others
Weather condition
CAVOK-Cloud and Visibility OK.
Flight mode
Climb, Cruise or Descent
Describe your event or Safety concern with your Own Words
The flight of the day with my Air 3 was to make a video of my home. I took off from my backyard between my house and shrubs bordered by a fence. Since the space was confined, vision sensors were disabled to avoid collision warnings. After take-off the aircraft maintained its position. I got a message GPS Weak. The drone became unstable laterally. Soon after, It started to drift towards the wall. It didn’t respond well to stick inputs. I landed the drone right away to prevent it from crashing into the wall.
Technical analysis
Hi Liam, thanks for the flight log you forwarded to us, It seems that your drone reverted to ATTI mode.
Contributing Factors : Caution message GPS weak with Vision Systems disabled → ATTI Mode.
We need a bit of knowledge to clearly understand the situation. A reminder, for those who already know. The drone takes data from various sensors to fly. They are :
1. GNSS (Global Navigation Satellite System). The drone receives signals from many satellites to compute a position on earth (Latitude, Longitude, Altitude, Time). Terrain, buildings or trees may block the signal of the satellites – The GPS signal is said to be line of sight dependent. The processor of the drone (Flight Controller) monitors the GPS position. If it becomes unreliable, GPS will not be used as a primary source of positioning. An alarm weak GPS or No GPS will be issued accordingly. GPS provides an accurate long-term position but updates slowly. As a consequence, it needs to be assisted by a vision positioning system during low altitude operations (0.5 m to 30 m) to improve stability.
2. VPS (Vision Position System). Uses the downward vision system (2 downward-facing cameras and a 3 Dimension infrared sensor) to evaluate the position relative to the ground. VPS tracks the ground patterns and measures the height with the 3 D infrared sensor. VPS can be failed (poor lightning, shinny surfaces, absence of textures) or disabled via RC 2 and Fly App.
3. IMU ( Inertial Measurement Unit ). Uses accelerometers and gyroscopes. Unlike GPS, IMU does not provide the position but the attitude (orientation) of the drone (pitch, roll, yaw). It keeps the aircraft level and stable in real time by stabilizing the pitch, roll and yaw angles. It also gives the acceleration and speed of the drone.
4. Barometer. It gives altitude by measuring air pressure. The air pressure is recorded at take-off point. Then, a drop of 1 millibar in pressure means an elevation of 28 feet.