I'm curious as well with this. Scary that this happened. Id like to know what could have possibly caused this.
Fog is bad news for intelligent drones like Spark. It dramatically lowers GPS signal and can easily cut it out completely, and it blocks the proximity sensors and cameras.
If it tries to RTH without GPS, it will still try to go up to an RTH height before moving. But with no GPS and no sight of ground, it relies on the IR range sensor on the bottom. The fog reflects this, so it looks like it's within a foot or two of the ground, and Spark goes up. It keeps doing this until the pressure sensor tells it that it has risen up too far. And there, it's basically stuck. It thinks it's on the ground,
and it thinks it's at max elevation. You should still have some remote control over it, though at reduced speeds while it's in RTH mode though. Even if you cancel RTH it may take some time to get it back down because it's going to be in "landing" mode (
and speed) all the way down because the IR sensors see fog as ground a few feet below it all the way down. But you need to take control and get it DOWN as soon as possible. If you've lost remote control over it your options are really limited, you just have to go about below it and wait for it to try an emergency landing due to low
battery.
This may not go well if it's too high up when it decides to come down, because it's not going to come down very fast and may lose power before reaching the ground. (so watch out for plummeting drones!)
Remember that if it has lost GPS
and can't use the forward and downward cameras to hold position (due to fog) then
it will be prone to drift in the wind, which may be quite high at 300ft. I think that's the biggest problem. It's hard to hear it when it's that far up, and the fog dampens the sound too, so you've got a tough job staying in the vicinity of where it's going to be coming down. (and it could be awhile if your
batteries have a lot of power left in them)
I think the moral of the story here is "Be
very careful when flying in foggy weather.
Fly (not RTH) your Spark back to you if you have the slightest hint of losing your remote/phone connection. Never fly into clouds where you can't see your Spark."
