Altitude behaviour on RTL using DO_LAND_START with RTL_AUTOLAND=2

What is the altitude behaviour when performing RTL using DO_LAND_START with RTL_AUTOLAND=2 please? I haven’t managed to find this in the documentation.

I assume that the target altitude is set to the altitude of the waypoint immediately after DO_LAND_START, rather than the value of ALT_HOLD_RTL?

If the aircraft is well above the target altitude, my experience is that it stays well above the altitudes set for the landing approach and doesn’t get down to low enough before reaching the LAND waypoint. I’m not sure what happens when this occurs (automatically does a go around or just keeps going straight and land in totally the wrong place?) as I’ve always taken manual control. (I only use the autoland for emergency fallback for a crash in a controlled location, although when testing it, it seemed to land reasonably well). I am intending to combat this by placing a LOITER_TO_ALTITUDE waypoint after DO_LAND_START at the start of the programmed landing approach. Is there a better approach?

Yes it aim for target altitude next to the DO_LAND_START from the current height and regardless of distance .

Yes it’s all based on TECS parameter setting for your plane sink rate.once reached land point it’s automatically Transition to Quad motor regardless of Target height,it never go around to reach the target altitude and i thing no protection for that…if may available some one can point here forum people will get benefit of them .

There is big issue that if plane is too far from land point if RTL activeted with DO_ LAND_START exist then it start follow the next Target altitude from current position. This logic should change for the plane safety.

It should be like this if I’m not wrong:
If too far from landing point RTL Is activeted it should maintain the ALT_HOLD_RTL up to the home and keep loiter until reach the next Target altitude then move on the next landing approach would be great.

@tridge your review please.

When you’re setting the waypoints for the auto-land look at the glide ratio. Plane won’t push the plane down or dive it like you might in manual or FBWA. The wiki suggests 10% as good start point. I’ve had some high lift, glider style winged planes that needed much lower glide ratios because they just didn’t descend.

Thanks for the replies.
@kalai1219 in Mission planner, the no field for the DO_LAND_START waypoint is labelled as altitude. As the mission jumps immediately to the waypoint after the DO_LAND_START when RTL is engaged, I assume that it is the altitude of this next waypoint that becomes the target altitude.

@Allister Yes, the thing is that when RTL is used (manually or failsafe) to trigger the automatic landing, the altitude at the time may not produce the glide slope found in the mission.

I think I’ll stick with including a LOITER_TO_ALTITUDE as part of the landing approach in case of RTL from higher altitude.

DO_LAND_START is just a flag in the mission. You are correct, the plane will fly to the next waypoint. It is also used as the marker in the case you abort an auto landing. Without it, if you abort a landing the plane will fly to the waypoint prior to the landing command. There is no limit to the number of waypoints after DO_LAND_START.