Unlike an airplane that can glide with the
engine off, or a helicopter that can land using autorotation, a multicopter is
completely uncontrollable when the motors or power are turned off. The
quadcopter can maintain stabilization if one of the engines fails. In addition,
a hexacopter or octocopter can make a soft landing with one inoperative motor,
but not in all cases (for example, if at least one blade breaks, the vibration
due to imbalance increases so much that the controller stops working and the
device goes into an uncontrollable fall). But there are already experimental
quadrocopters that can stabilize flight and land if one of the engines is lost.
Considering that a multicopter has a
considerable mass, a rigid body and rapidly rotating propellers, its collision
with people or vehicles can lead to negative consequences. Therefore, flying
over people or over highways is not recommended. It is advisable to plan the
flight path so that, if necessary (for example, when the battery is
discharged), there is a place below for a safe landing.
The human factor is also important. A modern
flight controller is almost as good as a desktop computer in terms of
configuration complexity and the number of flight modes. Inattentive reading of
the documentation, failure to perform the necessary actions (for example,
calibrating the compass during setup) can lead to uncontrolled flight and loss
of the device. Departure of the device beyond the range of the remote control
in the absence of the GPS return mode is also one of the reasons for the loss
of devices.
For safety reasons, some models of remotely
controlled multicopters are equipped with redundant navigation and positioning
systems, intelligent robotization elements that contribute to the aircraft's
self-determination of obstacles on the flight route and their overflight,
propeller covers or the entire aircraft, and self-return to the launch site if
the control signal is lost.