# Estimator watchdog: velocity and horizontal position check bit \>\> descend (fast...)) **URL:** \ **Category:** PX4 Autopilot\ **Created:** [January 31, 2019, 12:41pm UTC](https://discuss.px4.io/t/estimator-watchdog-velocity-and-horizontal-position-check-bit-descend-fast/9437 "2019-01-31T12:41:10Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Galloist](https://discuss.px4.io/letter_avatar_proxy/v4/letter/g/85e7bf/32.png) [@Galloist](https://discuss.px4.io/u/Galloist)\ **Post date:** [January 31, 2019, 12:41pm UTC](https://discuss.px4.io/t/estimator-watchdog-velocity-and-horizontal-position-check-bit-descend-fast/9437/1 "2019-01-31T12:41:10Z")
Hello everyone, I´m not sure what exactly caused such a sudden descend. Plane: History of 169 flights/missions. 167 successful and 2 problems (logs links posted here). 1200 mm (47 in) wingspan flying wing; 1,7kg; 3DR Pixhawk mini. The plane entered Descend Mode while executing a mission @ 230m AGL (about 1000m ASL). I can see that the altitude setpoint goes to 0m ASL causing the plane to rush to the ground. I would be immensely thankful if someone could help me to figure out. 2019 incident: [https://review.px4.io/plot\_app?log=39401392-e997-46cf-a2e3-d76c68537d1d](https://review.px4.io/plot_app?log=39401392-e997-46cf-a2e3-d76c68537d1d) 2018 incident (apparently the same issue but recovered before descend mode kick in): [https://review.px4.io/plot\_app?log=a6f9471d-1a1c-421c-9bee-5afae6f5fcc8](https://review.px4.io/plot_app?log=a6f9471d-1a1c-421c-9bee-5afae6f5fcc8) ---
**Author:** ![Galloist](https://discuss.px4.io/letter_avatar_proxy/v4/letter/g/85e7bf/32.png) [@Galloist](https://discuss.px4.io/u/Galloist)\ **Post date:** [January 31, 2019, 12:52pm UTC](https://discuss.px4.io/t/estimator-watchdog-velocity-and-horizontal-position-check-bit-descend-fast/9437/2 "2019-01-31T12:52:06Z")
I have already updated the firmware on the board. The airframe was ok regarding vibrations, flight characteristics and magnetic interference. The day the plane misjudges the altitude setpoint, we had thermal column of ascending air on the area. Maybe this is the start of the problem, or maybe the fact that the plane was running older firmware. ---
**Author:** ![Antiheavy](https://discuss.px4.io/user_avatar/discuss.px4.io/antiheavy/32/6398_2.png) [@Antiheavy](https://discuss.px4.io/u/Antiheavy)\ **Post date:** [February 2, 2019, 11:36pm UTC](https://discuss.px4.io/t/estimator-watchdog-velocity-and-horizontal-position-check-bit-descend-fast/9437/3 "2019-02-02T23:36:00Z")
you should try the newer 1.8.x firmware. There was a lot of bad stuff for fixed wing in older firmware, especially certain EKF2 and PX4 failsafe behavior. In particular this change allowed relaxing a number of settings for fixed wing vehicles: > ---
**Author:** ![Antiheavy](https://discuss.px4.io/user_avatar/discuss.px4.io/antiheavy/32/6398_2.png) [@Antiheavy](https://discuss.px4.io/u/Antiheavy)\ **Post date:** [February 2, 2019, 11:43pm UTC](https://discuss.px4.io/t/estimator-watchdog-velocity-and-horizontal-position-check-bit-descend-fast/9437/4 "2019-02-02T23:43:39Z")
However, the root cause of your issue in the most recent log is some sort of problem on the aircraft. Some unusual Y-accel and gyro measurements when the failsafe kicked in, some strange vibration or flutter? ![](https://discuss.px4.io/uploads/default/original/2X/c/c3bc509ac851e7ed54acacdbeb16a5b14a79c40e.png) which probably is what is causing the EKF starts getting upset: ![](https://discuss.px4.io/uploads/default/original/2X/d/d7d079b47af7e8a6fda5bf3a40d2491390115e92.png) ---
**Author:** ![Galloist](https://discuss.px4.io/letter_avatar_proxy/v4/letter/g/85e7bf/32.png) [@Galloist](https://discuss.px4.io/u/Galloist)\ **Post date:** [February 4, 2019, 12:40am UTC](https://discuss.px4.io/t/estimator-watchdog-velocity-and-horizontal-position-check-bit-descend-fast/9437/5 "2019-02-04T00:40:27Z")
> [@Antiheavy](#): > > hen the fa Thanks a lot for the reply. I will check the vibrations.