Crashed Landing: Potential Thrust Loss

I just tested my 600 helicopter today and it all went well in stabalise mode until it crash landed during alt hold.

The aim of today’s flight is to get closer to autonomous flight. The plan to get there involves flying stabalise, then althold, loiter and finally auto.

While testing today, the stabalise mode worked perfectly. When we switched to alt hold mode, it worked well most of the time until we started to descend with alt hold. The heli motor just stopped mid flight at around 30m altitude and dropped all the way down to the gound. It was a pretty bad crash.

The pilot notified us that during this crash, he had no controls over the helicopter. This includes motor throttle and also swashplate movement.

As we analysed the log data, we noticed that once we started descending in the ALT HOLD, there was an error of “potential trust loss” which is followed by “radio loss” and “compass loss”. We are not really sure what is the problem here.\

At first, we thought that it is a problem with traditional helicopter landing detection. But we are not 100% sure if this is the case.

I have attached the flight log in the link below.

We appreciate if anyone can kindly help guide us to what the problem may be.

Please give permission to access your file on google drive.

I have granted permission and changed to public access. Sorry for the inconvenience!

No worries. Sorry about your crash. I will look at this later today.

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Hi @jippers ,
it was a commanded shut-down due to setup error.
You have set motor interlock on channel 3 (throttle) while it should have been left at default on channel 8 (or any other channel associated to a 2 positions switch-surely not to a stick channel!).
As soon as the pilot lowered the collective (so channel 3) motor went off:

“Potential thrust loss” is a direct consequence of rpm dropping (and so lift) after motor shutdown and collective maxing out. The other messages are subsequent the impact:


Thank you @Ferrosan!

That makes sense!

I never fully understood motor interlock. Does that mean motor interlock acts like an additional safety switch?

What is the main difference between motor interlock and safety(arm/disarm) switch?

Arm/disarm and motor interlock are unrelated to each other in what their functions are, arming switch (or procedure- by applying right yaw) performs several checks on internal status of flight control (like GNSS fix, compass health, params sanity and many others) before letting you arm the aircraft for takeoff and flying.
Motor interlock allows for switching on and off the engine, if flight control is in armed state.
So yes, it is an additional safety switch on “main” power source.

They are subsequent to each other, in other words you will not be allowed to switch motor interlock on if the helicopter is in disarmed state.


Thank you for the help @Ferrosan!

Now I understand the difference between the arm/disarm and motor interlock switch.

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