Plane crash - altitude loss after climb and dive

My plane was on an auto flight using a Pixhawk running 3.8. It was flying at 25m then next waypoint up to 58 m to clear some pylons. The next waypoint was back to 25m but it never recovered from the dive and hit a small tree about 3m from the ground (no damage).

It has an Unmannedtech Pixhawk ( and NEO M8N.

As you can see from the attached kmz file it seemed to be a bit low all the time but showed no sign of levelling out after the dive.

What made this happen?

Download original .bin DataFlash log and mission file in ZIP file here

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I personally don’t have the tools handy to analyze a text-converted log file… would you also upload the original .bin DataFlash log?

(Of course others may be able to use a text .log file and help you as-is. No problem if you want to wait for them instead.)

It looks like the flight started in Manual mode, flew the plane up to 58m and then invoked Auto mode, which brought the plane down to 25m.

Do you have the mission file you can post? Was it made with Mission Planner or some other GCS app?


Original .bin DataFlash log uploaded. New link in posting.


Original mission file made with Mission Planner. Now in zip file to download with original .bin DataFlash log in original posting.


Thanks for posting the mission plan. It appears that your change in altitude was too abrupt for the distance between waypoints 19-22 and 33-36. You need to keep the Gradient % within the capabilities of the aircraft…especially when flying low like 20 meters altitude. Try using Waypoints that produce a Gradient % of <10% or even <5%.

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I’m not sure that is the problem as this plane has dived many times up to 20 degrees with no issue levelling out. Looking at the kmz file it looks like there was no attempt to level out at all.

Perhaps there was an inaccuracy in the actual ground height. I typically fly at a higher altitude like 100m, which may negate any error. At Waypoint 21, you can see the “Crash detected” entry if you blow up the altitude chart like below. Perhaps the terrain has an effect on your detected altitude.

It looks like you live close to the English Channel. These are places I have only read about but never visited.

I haven’t tried it but there is also an Automatic Terrain Following feature available for fixed wing aircraft.