DJIs' are known to having "fly aways" with their quadcopters. Most of the time it is just simply due to pilot error and lack of knowledge of the platform. The Phantom 1, FC40, 2, 2 Vision, 2 Vision Plus, and all the Phantom 3 series uses the same flight controller, the Naza GPS platform.
I'll be sharing ways to prevent a drone fly aways and what to do when you are having one.
Always Wait for GPS and Home Lock:
When you start up your Phantom, it immediately tries to connect to satellites to determine where it is on the map. You will notice it has gotten sufficient amount of satellites as the Phantom will blink green very quickly. This is telling you that it has remembered where the "home" is, meaning the position where it can turn to if it loses connection with the transmitter. This is useful in case you lose orientation or the worst case, a fly away. Sometimes the flight controller can detect that something is going wrong and hover its self then finds the closest way back to home.
Calibrate the compass:
Before any flight, it is important to do a compass calibration, especially when you have changed locations. Simply flick the top right switch in between GPS mode and Attitude mode rapidly until the Phantom lights turn yellow. Pick up the Phantom and rotate it 360 degrees’ perpendicular to the ground. Once you have completed that, flip the Phantom with its landing gear away from you and the battery compartment pointing down, then complete another 360-degree turn.
The quadcopter should notify you that calibration was successful if green lights blink quickly at the end. If you get an error (rapid blinking red lights) then you may need to connect your Phantom to the Naza configurator and do an Advanced IMU calibration. As the last note, remember to always perform a compass calibration after tweaking or working on the Phantom.
Recovering from a fly away:
In some cases, the Phantom continues to drift to a direction on its own and does not detect something is wrong. In this case, quickly switch to manual mode. When you switch to manual mode, you tell the Phantom to stop relying on GPS and only fly with gyro and compass. However, if you never had any experience with flying in manual mode do not switch to this mode! Flying in manual mode is totally different than flying in any other modes, so switch to this mode with caution! For people who can't fly in manual mode, the only thing you can try to do is turn off the transmitter and hope the Phantom will return to home.
Know about frequencies:
This is probably one of the biggest mistake pilots can do. It is super important to understand how certain frequencies can affect your quadcopter when you fly; for example, cellular towers, WiFi frequencies, and the landscape. You would never try to fly a Phantom 2 with a Phantom FC40. Why? This is because the Phantom 2 uses 2.4ghz for controls, whereas the Phantom FC40's camera also uses Wi-Fi on 2.4ghz to live stream video.
Many pilots think that 2.4ghz with frequency hopping should be fine, but this will not work with video transmissions. You may be able to fly still fly your Phantom until you fly a little further then your Phantom will start to jitter and "have a mind of its own" this is because the video transmission has cloaked your 2.4ghz controls and is reacting to the video's frequency that happens to be the same as your control signals.This can also happen if you fly too close to houses that has Wi-Fi broadcasting.
Cellular towers can target both the GPS signal and the control signals. How? It overwhelms the Phantom with power frequencies that manages to bypass the phantom's frequency filtering system and cause it to receive false information like giving it a 'new GPS location'. This is a terrible situation as now the Phantom will try to fly across the globe to return to its 'new' GPS Hold.