I have my max altitude set at 500m. I have my RTH setting at 400'.  A few weeks ago, I started a flight at 6100' and flew up the side of the mountain until the max altitude setting had been reached at 1642' above my starting position. My question is, what would have happened if I had hit the RTH button? Would the drone have tried to descend to 400' and thus crash into the mountain? Or would it have just flown back at its present altitude till overhead then descended? This last situation would have had me way over FFA RegS.  Which also means if I set the RTH at 500m, the RTH activation would surely have me at odds with the FAA. I had a great flight but had I lost connection with the drone, I think I would have left it on the mountain. What do you think?

First off, the max height is relative to ground and not relative to sea level. Then if you go max height and hit RTH, and I may add you are in p mode where all sensors are enabled and monitored, the drone will descend to local RTH altitude, plot the straight course and expect no obstacles in the path. If there is an obstacle, I expect the drone to stop, hover and emit an obstacle warning.

If the aircraft is above the height set for RTH, then it will stay at its current height and fly straight home from there.
The height you set for Max' altitude is the height above the take off point. If as you suggest you start at the base of a mountain, and you fly up that mountainside, say 100 ft above the ground. Once the aircraft reaches 1640ft (lets say a gentle slope and it's one mile from take off point) it will go no higher. If it was to initiate an RTH, then as its above the 400ft you set then it will stay at that altitude (1640ft) and fly one mile horizontally back to the take off point, and then land. Which means for a lot of the journey back you would be well above the FAA limit.

Put simply RTH returns at the higher of the height the drone is at and the set RTH height. It will never decend before returning to home.

WindSoul Posted at 2017-1-12 07:41
First off, the max height is relative to ground and not relative to sea level. Then if you go max height and hit RTH, and I may add you are in p mode where all sensors are enabled and monitored, the drone will descend to local RTH altitude, plot the straight course and expect no obstacles in the path. If there is an obstacle, I expect the drone to stop, hover and emit an obstacle warning.

" the drone will descend to local RTH altitude, "

It will not descend if it is above set RTH altitude.

There is a video of this flight I posted. Its good to know it would not have tried to decend before coming home. If I had lost connection I would expect to be able to get it back and drop the drone to an appropriate altitude.

Trackerputnam Posted at 2017-1-12 19:03
There is a video of this flight I posted. Its good to know it would not have tried to decend before coming home. If I had lost connection I would expect to be able to get it back and drop the drone to an appropriate altitude.

The important thing to keep in mind is that the aircraft has no idea what altitude above sea level it is flying at. All it knows is how far above or below the take off point. And RTH means what it says, if it is invoked, the aircraft flies back to where it took off from.

Aardvark Posted at 2017-1-12 08:09
" the drone will descend to local RTH altitude, "

It will not descend if it is above set RTH altitude.

Good to know. I thought it will check the RTH before entering horizontal flight.