I need to use my Y6 (APM 2.6; AC 3.1.5) for surveying and need to be able to automate missions, but today my auto mission didn't complete and RTL failed - it was as though the flight mode changed to loiter and ignored RTL signals. I've spent several hours trying to work out what went wrong, but still can't get to the bottom of the multiple failures so I'd really appreciate some input.
I've previously flown successful test missions in Auto mode, which were also designed in MP (V1.3.10) using the Survey(grid) tool. My WP file is attached; I started with a takeoff WP then climbed to the target altitude. WP 2 and 3 should have adjusted the the flight speed and camera triggering distance, and then it should have headed for WP 4. Instead, it just sat at the target altitude above WP1 (as though in loiter). After a few minutes, when it became clear that the copter wasn't going to complete the mission, I tried to initiate RTL (firstly via Ch. 5, then by a Ch. 7 override), but had no effect on the copter so I switched to loiter and landed.
I've got two questions:
(1) Why did the auto mission fail?
(2) Why were the multiple RTL commands ignored?
(I tested the RTL via Ch. 7 a few days ago which worked fine. Subsequent testing shows RTL commands sent from the Tx are received the APM and displayed on the GCS. I thought the most likely explanation was GPS failure had terminated the mission and prevented the RTL, but the copter held position for ~4 minutes in light winds, the sat count was 8-10 and the GPS hdop was <1.80 throughout the entire flight. I don't see why it should matter, but is was ~36 degrees C, and over the coarse of the flight there was ~10 m barro drift.) Reviewing the log (attached) shows the correct flight modes were selected.)