Why do they fly away? What happened?
Almost everyone experiences a flyaway. Its bound to happen, its a matter of probability. But why does it happen? There are too many reasons to list, but a few of the common reasons are.
1. The compass begins to fail before giving the user a fault signal and causes the flight controller to become disorientated because of conflicting info with the GPS. The Blade and the DJI series have this issue and its something that can be caught easier with Blades compass error detection.
2. ESC failure can be a nightmare without proper testing equipment. If you cannot induce load and examine the esc through thermal imagery you cannot diagnose a failing esc before it happens. The failing esc has higher resistance and begins to get hot and that motor receives less power, the flight controllers gyro begins to up power to keep a level flight while the failing esc's power output stays the same causing the craft to tilt and off it goes into the horizon. Or the craft simply noze dives into the ground at high speed.
3. Oscillations and vibrations. Motor vibrations can induce emf signals that the esc may interpret as brushless motor EMF signals and stall your motor and even make it run backwards or overheat. These vibrations traveling through the body make their way to the flight controller and just imagine what kind of influence that has on a gyro stabilizer built into the flight controller. The dreaded flip of death that has claimed so many aircraft. Balance those props!!!!
4. EMI, electro magnetic interference. This can be caused by outside sources or by additional flight gear. FPV , or first person viewing transmitters can over whelm flight receivers. Compass errors can be induced by gimbals and brushless motors. Tracking units and cameras can operate on nearly the same band as GPS. when you experience lock out there may be nothing you can do but watch it fly away.
I test all completed drones/multicopters that I build for all of the above. I hope to save someone the grief of watching their money fly away.