Crashed in take off with firmware "Arduplane 3.7.1",Why?

Hello everyone! Can anybody help me analysis why my palne failed to climb in the begining of take off ?
Here is my log and tlog:
and flight vedio:

I noticed again in this log that POS.RelAlt = 0 for the whole flight, while POS.Alt is non-zero. Remeber that we found this on a previous problem that you raised: Big alt lose when switch into RTL

Has your firmware been custom-modified? If yes, will you try the latest standard firmware versions (ArduPlane 3.8) and see if that fixes the problem?

@hunt0r Thanks! The log you see :

I use the firmware “ArduPlane 3.7.1”.I do not correct it’s code.Is it maybe a bug of “ArduPlane 3.7.1”

I have tested the “ArduPlane 3.8”,it fixed the problem( see following figure).

Interesting, when I did an auto analysis on my crash after takeoff I got this:

Size (kb) 70284.86328125
No of lines 974877
Duration 0:17:51
Vehicletype ArduPlane
Firmware Version V3.8.2
Firmware Hash f829f561
Hardware Type
Free Mem 0
Skipped Lines 0
Test: Autotune = NA -
Test: Balance/Twist = NA -
Test: Brownout = GOOD -
Test: Compass = FAIL - Large change in mag_field (64.92%)
Max mag field length (744.10) > recommended (550.00)
Test: Dupe Log Data = FAIL - Duplicate data chunks found in log (444120 and 585587)
Test: Empty = GOOD -
Test: Event/Failsafe = GOOD -
Test: GPS = GOOD -
Test: IMU Mismatch = WARN - Check vibration or accelerometer calibration. (Mismatch: 1.14, WARN: 0.75, FAIL: 1.50)

Test: NaNs = FAIL - Found NaN in POS.RelOriginAlt

Test: OpticalFlow = FAIL - FAIL: no optical flow data
Test: Parameters = GOOD -
Test: PM = NA -
Test: Pitch/Roll = NA -
Test: Thrust = NA -
Test: VCC = UNKNOWN - No CURR log data

I set " ‘AHRS_EKF_TYPE’=2, ‘EKF_ENABLE’=1, ‘EK2_ENABLE’=0, in firmware ‘ArduPlane 3.7.1’", but " ‘AHRS_EKF_TYPE’=2, ‘EK2_ENABLE’=0, ‘EK3_ENABLE’=1, in stable firmware ‘ArduPlane 3.8’".

I guess that

is related to EKF parameters I set.

@innovation Thanks for the explanation about the EKF_ENABLE and AHRS_EKF_TYPE. I remember a previous conversation about this, but I don’t remember if it was conclusive.

So is your problem solved now, with ArduPlane 3.8?

@Chad_Frazer Sorry, I didn’t understand… are you linking information from this post? Or something else?

@hunt0r Yes,“The POS.ReAlt=0” is revolved in ArduPlane 3.8.

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