During a pre-programmed autonomous flight, the UAS went behind a hedge of tall trees that the remote pilot thought would be low enough to ensure VLOS for the flight height (100m).
CHIRP Comment
The Board had the following comments:
When planning autonomous flights, it is difficult to predict the height at which the aircraft will stay in line of sight of the pilot, particularly if the mission includes a controller handover. To avoid brief moments, like in this report, when an aircraft is obscured during its flight by a tree or a building that is in front of it, always add a few meters to the planned height of the operation if you are in doubt.
If it is a particularly complex location, fly the planned route manually first to check that it remains in Visual and Radio Line of Sight, note the height and other route details before loading the correct parameters into the autonomous flight software accordingly.
It is important to always include in the pre-flight checks the setting for what the aircraft is programmed to do, if it loses the C2 link. If there is a momentary disconnect, it is vital that the pilot is not then surprised by what the aircraft does.
If you are planning a mapping mission and it looks as if the aircraft is going to go behind an object, don’t forget that you have the option of pressing pause which will then give the pilot an opportunity to change their position to retain line of sight.
Always remember that the drone controller often shows the height of the aircraft above its take off point, rather than above the ground it is flying over or sea level.
