Altitude source for HUD ( shows GPS value sometimes, and resets to zero later)

Sometimes, Altitude shown in HUD display of Mission planner is GPS altitude. It shows zero altitude upon restarting. What can be the cause?
How to do away with it?
If I takeoff when it shows GPS altitude in my HUD, will it be able to land in RTL?

The altitude gets automatically reset every time directly after arming. This is not bug, it´s a feature :slight_smile:
That altitude is the altitude above home. And home is per definition the place where you armed the vehicle.

And please update to ArduCopter 4.2.2 the version you are using is very old.

Hi! We have deployed it commercially, and have some constraints not to update it. It get your point that it is a feature. However I am concerned what if someone takes off while HUD is showing GPS, and turns it into RTL, will it land back at same position? (Intutively I feel it shall since it will return to takeoff altitude, showing same 894 m (in our case on GPS)

Yes, it will not be a problem.