P4P crash: why???

[leoconti]

I was passing under a little bridge over a small river in Italy, as soon as the Phantom enters under the bridge it stopped and begun to rise... since it was about 2 meters under the "ceiling", after a couple of seconds it hit the ceiling and splashed in the water... I recovered it after 3 hours, dried with mild air and keeping it in the rice for a few days. When I tried to switch it on the drone was ok, perfectly flying, but there is an error "no image transmission" and "gimbal disconnected". Now, since I've seen in the flight record that it suddenly lost satellite signals, dropping from 14 to 4... and right after that it begun the suicide rise, I was wondering if that behavior is normal or is a failure, having any chance to claim a warranty substitution...

 

[Meta4]

I was passing under a little bridge over a small river in Italy, as soon as the Phantom enters under the bridge it stopped and begun to rise... since it was about 2 meters under the "ceiling", after a couple of seconds it hit the ceiling and splashed in the water... I recovered it after 3 hours, dried with mild air and keeping it in the rice for a few days. When I tried to switch it on the drone was ok, perfectly flying, but there is an error "no image transmission" and "gimbal disconnected". Now, since I've seen in the flight record that it suddenly lost satellite signals, dropping from 14 to 4... and right after that it begun the suicide rise, I was wondering if that behavior is normal or is a failure, having any chance to claim a warranty substitution...

You've already found that the bridge blocked the Phantom's view of the sky and GPS satellite reception.
This would have left your Phantom in atti mode and subject to drifting with any wind but it doesn't explain the Phantom climbing.
There's a good chance the cause will be in the recorded flight data.

Go to DJI Flight Log Viewer
Follow the instructions there to upload your flight record.
Come back and post a link to the report it provides.

 

[leoconti]

Thank you Meta4, I'let you know the results...

 

[leoconti]

Hello Meta4, this is the link...
DJI Flight Log Viewer - PhantomHelp.com
Hope you have any suggestion. Thanks.
Leonardo

 

[Pharm]

You've already found that the bridge blocked the Phantom's view of the sky and GPS satellite reception.
This would have left your Phantom in atti mode and subject to drifting with any wind but it doesn't explain the Phantom climbing....

Either that or it lost contact with the RC and RTH initiated. That would explain the climb.

 

[Bakersfield Quad]

RTH is a possibility, but the log shows no changes in altitude, until the last 1/10th second, is shows it going down. I suspect that the altimeter was getting fluctuating pressures, near the water and bridge, it tried to stay at what it thought was the correct altitude.

 

[Meta4]

Hope you have any suggestion. Thanks.

Here is the relevant data:

Everything below the yellow line is after the crash and shows the Phantom tumbling into the water
You can see the number of GPS sats drop and the Phantom slips into atti mode.
The left stick remains in the centre (far right column - stays on 1024)
Altitude drops from -4.9 feet to -5.6 feet, then rises a little to -5.2 feet (pink)
This rise is approx 0.12 metres which isn't enough to hit the bridge if it was 2 metres below the deck.
Perhaps the underside of the bridge was not flat and there wasn't 2 metres clear space?
If close to the bridge deck, there may be some suction force with the props pushing air down from above the Phantom.
This is sometimes seen with people flying indoors - their drones get sucked toward the ceiling.
The barometer reading might not give an accurate height measurement in the semi-enclosed space near the bridge deck.
Pulling air from above the Phantom to push downwards could reduce the air pressure above the Phantom and make the barometer show a slightly smaller rise?

Climbing for RTH is not a possibility as the flight record is complete past the small climb till the end with no indication of RTH happening.
Also, with only 3 sats, the Phantom can't RTH as it has no sense of position.

 

[leoconti]

So, could it be a failure in the positioning system? Anyway I have send it to assistance... let's see what is their analysis... hoping the problem will be covered by warranty. Thank you for your support.

 

[Meta4]

So, could it be a failure in the positioning system?

Position holding did not fail.
Out in the open, everything would have been fine but once the Phantom loses GPS and slips into Atti mode, there is no position holding ability.
The VPS sensors are not reliable in poor light or on water so that won't be much help either.

 

[BudWalker]

.....
The VPS sensors are not reliable in poor light or on water so that won't be much help either.

But the VPS sensors might be reliable. And, in this case it shows the rise seen by the pilot. Your theory about increased air pressure seems right here as the OSD.sWaveHeight shows the AC rising in order to compensate for the increased air pressure.

I thought the OSD.sWaveHeight value comes from the ultrasonic sensor on the bottom. Not so?