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Almost Crashed - RTH Learning Opportunity

cobra46

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Hi folks!

This evening my son and I were flying our Mavics in front of our house and things almost went very bad. I want to share my experience in the hopes someone else doesn't replicate my stupidity.

Normally I takeoff from the street in front of my house and land manually in roughly the same spot. A few times I have tested the RTH function to make sure it works and that I understand how it works. All of these tests were without incident. I also typically land with 20-25% battery remaining.

Tonight for some stupid reason I decided to takeoff from the space between our cars and the open big garage door. There is roughly a 6-8' space between the bumpers and the opening/house. At the time, my thought process was that I would land as usual in the street when the battery was low. Takeoff went smooth enough as did the flight.

My low battery warning is set for 30% and my critical battery warning is set for 10%. As I passed 30% I started flying closer and closer to the landing spot. My other son's friend was leaving and we wanted to get some shots of him driving away. Before I knew it, I was at 10% and the drone was headed to home. At first, I thought it was no big deal as I was only at like 50 feet high and 30 feet or so away so I can quickly land like usual. Well...the drone had other plans such as landing at it's home point. It was headed towards our cars and the house no matter how hard I tried to land. While I trust the RTH function, I wasn't sure if it would miss the cars and house while landing on it's own.

Anyway, this is where things got way scary. I was able to fly forward and backward but not descend lower than about 6' nor hover. So as i was rocking it forward and backward, all I could think to do was hand grab it. I reached up with my right hand and grabbed it tightly so my left hand was free to pull back on the stick. Turns out it doesn't shut off when in this emergency return to home situation. Instead, it went to full power and ultimately slipped my grasp. Now I'm really s***ting bricks. Meanwhile, my son is wondering what is going on. I was unable to explain my situation but that I needed help. He quickly landed his and made a grab for mine. I told him to grab in firmly as it pulled hard. He had hand grabbed mine earlier and I was able to pull power like usual. As soon as he grabbed it his finger was nicked by a prop. I had to pull both sticks down and in to kill power.

Rightfully so, he started unleashing a tirade of four letter words directed at me and my stupidity.

The after incident analysis revealed a theme common to many accidents which is multiple things went bad at the same time.

1: Poor choice of takeoff location
2: Distracted attention to battery level to 'get the shot'
3: Not understanding the behavior of a critical battery return to home
4: Not immediately knowing that pulling the stick back will NOT kill the power

I know I will never make this mistake again and I'm grateful my son wasn't seriously cut and my drone is not hurt. Now it's time to read more about the behavior of the drone during a critical low battery RTH.

I truly hope my situation helps others avoid my near crash.
 
Last edited:
...Anyway, this is where things got way scary. I was able to fly forward and backward but not descend lower than about 6' nor hover. So as i was rocking it forward and backward, all I could think to do was hand grab it. I reached up with my right hand and grabbed it tightly so my left hand was free to pull back on the stick. Turns out it doesn't shut off when in this emergency return to home situation. Instead, it went to full power and ultimately slipped my grasp.
Wow! I had no idea you could not power it down, normally, in an emergency RTH situation either.
Thanks very much for sharing this experience. You will surely prevent some others from getting in similar predicaments.

I have lot's of questions, but I'll just stay quiet now and let the more knowledgeable fliers give tips on ways you could have controlled the Mavic in that RTH gone bad... ?
 
Wow I want to know how to cancel the RTH in that situation now. How can we make the emergency landing ourself?
 
It is possible that in the heat of the moment I thought I was pulling the stick back and I was really pushing it forward. Humans can do crazy things in emergencies without realizing it.

I will read about it and test it when my home point is in a safe location.
 
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Experience is a hard way to learn.
It test first and teaches later.
 
Thanks for sharing! For me these types of stories are excellent reminders.
 
That's a bit odd ... as according to the user guide ( page 14 ) unless the MP has decided it only has enough power to land then you should always be able to cancel the RTH and just land manually .....

Have you looked at the .txt file in MavicHelp https://www.phantomhelp.com/LogViewer/Upload/

it might provide a bit more detail of your flight.
 
I thought to cancel RTH you hit the pause button or you can flip the switch to sports mode and then back to PMode. I heard so many RTH horror stories I'm scared to use it now. That was one of the main features I wanted this drone for. So I can fly it around then hit RTH and it comes back. Not so, I do all my come backs manually now.

I did learn that in criticle battery situations it will shut off the Obsticle Avoidence and start dropping the bird to the ground fast. I tried to stear it and ended up hitting my fence. It was metal as well so there was even a compus error notice right around the time it crashed. Go figure.
 
I can with absolute confidence say that my RTH has worked perfectly every signal time, have you tried to update the RTH during the flight ?? or used your mobile as the RTH point ?
 
Dji has a built in safety feature. On the controller if you move both the control levers simultaneously down and in to their corner positions the motors will stop immediately. Some new flyers do this by mistake and their aircraft falls from the sky. The manual has more information on this.


Sent from my iPhone using MavicPilots
 
I've always told my kids that experience is what you get right AFTER you needed it. This was one of those situations.

Yep, experience is a tough teacher...she gives the exam first, and THEN teaches the lesson!
 
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Dji has a built in safety feature. On the controller if you move both the control levers simultaneously down and in to their corner positions the motors will stop immediately. Some new flyers do this by mistake and their aircraft falls from the sky. The manual has more information on this.


Sent from my iPhone using MavicPilots


That's only true if you select that option. The other option is that it will not shutoff the motor in midair unless it detects a fault, such as crashing into tree branches, then you can move the sticks together to shut it off.
 
Thanks for sharing! My guess is that you pushed up on the stick instead of pulling down. You can see your stick movements on the flight log on your phone. Your story should keep us all on our toes!
 
That's a bit odd ... as according to the user guide ( page 14 ) unless the MP has decided it only has enough power to land then you should always be able to cancel the RTH and just land manually .....

Have you looked at the .txt file in MavicHelp https://www.phantomhelp.com/LogViewer/Upload/

it might provide a bit more detail of your flight.

I haven't yet.
 
I thought to cancel RTH you hit the pause button or you can flip the switch to sports mode and then back to PMode. I heard so many RTH horror stories I'm scared to use it now. That was one of the main features I wanted this drone for. So I can fly it around then hit RTH and it comes back. Not so, I do all my come backs manually now.

I did learn that in criticle battery situations it will shut off the Obsticle Avoidence and start dropping the bird to the ground fast. I tried to stear it and ended up hitting my fence. It was metal as well so there was even a compus error notice right around the time it crashed. Go figure.

I had read about switching from P to S mode but in my panic I forgot which is also why I didn't hit the pause button. I will test these this evening when I get home.

My previous RTH tests were very successful with the Mavic landing within a few inches of takeoff location.
 
I can with absolute confidence say that my RTH has worked perfectly every signal time, have you tried to update the RTH during the flight ?? or used your mobile as the RTH point ?

Not sure who this question is directed to. I have not used my mobile as a return to home point but this isn't a bad idea.
 
Dji has a built in safety feature. On the controller if you move both the control levers simultaneously down and in to their corner positions the motors will stop immediately. Some new flyers do this by mistake and their aircraft falls from the sky. The manual has more information on this.


Sent from my iPhone using MavicPilots

This is how I ended up shutting it down.

I read all the documentation cover to cover so I have been exposed to all the information. Can't say I retained it all unfortunately.
 
The landing behaviour of the Mavic is possibly one of the things that takes some getting used to. Under normal situations the aircraft will descend until it's 50cm from the ground, if you continue to hold the left stick down it will descend to the ground. Once this starts descending past 50cm if you let go of the left stick it will continue to land. Then shut down.

If you try to hand catch while it is decemding and the VPS sensors detect the 'ground' too quickly it automatically increases power in order to arrest the decent, if the ground continues to close in then it will increase power again to arrest the decent. So if it detects your hand approaching and you have the left stick held down it interprets this as a rapidly approaching ground and apples more power, if you now have a hold of it, it can't get away to provide more separation, so it piles in the power as it thinks it's about to hit the ground! Result is you have a hold of a Mavic that has applied full power to arrest its decent, in this case even with the stick held back it will apply a lot of power to arrest its perceived impact with the ground.

You can try this if you're brave descend to a hover put your hand under to catch it and then pull the left stick back, move your hand up and get a hold of it, the Mavic will try to accelerate away, it can pull quiet hard so be careful!!
 
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@JohnC , in the example you give above, will the Mavic eventually shut off?

I have watched several videos of people hand catching Mavics, and I suspect most haven't take then time to turn off VPS (or claim they haven't). So how do you shut it off when you have a drone in one hand and a controller in the other?
 
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