# Error SITL **URL:** \ **Category:** Uncategorized\ **Created:** [April 15, 2020, 11:19pm UTC](https://discuss.px4.io/t/error-sitl/16255 "2020-04-15T23:19:06Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Juatarto](https://discuss.px4.io/letter_avatar_proxy/v4/letter/j/b9bd4f/32.png) [@Juatarto](https://discuss.px4.io/u/Juatarto)\ **Post date:** [April 15, 2020, 11:19pm UTC](https://discuss.px4.io/t/error-sitl/16255/1 "2020-04-15T23:19:06Z")
Hello, I am trying to use QGC to do missions, but when I start a mission I get these errors. What are they for? What do they mean? ERROR [sensors] Accel #0 fail: TIMEOUT! ERROR [sensors] Sensor Accel #0 failed. Reconfiguring sensor priorities. WARN [sensors] Remaining sensors after failover event 0: Accel #0 priority: 1 ---
**Author:** ![JulianOes](https://discuss.px4.io/user_avatar/discuss.px4.io/julianoes/32/30_2.png) [@JulianOes](https://discuss.px4.io/u/JulianOes)\ **Post date:** [April 16, 2020, 6:31am UTC](https://discuss.px4.io/t/error-sitl/16255/2 "2020-04-16T06:31:33Z")
What SITL (jMAVSim or Gazebo or something else) are you using? What version of PX4? It basically means that the accel data had a timeout. ---
**Author:** ![Juatarto](https://discuss.px4.io/letter_avatar_proxy/v4/letter/j/b9bd4f/32.png) [@Juatarto](https://discuss.px4.io/u/Juatarto)\ **Post date:** [April 16, 2020, 12:09pm UTC](https://discuss.px4.io/t/error-sitl/16255/3 "2020-04-16T12:09:36Z")
I have created a bridge between PX4 and FlightGear to use it. Right now I run PX4 with “make px4\_sitl none”, PX4 receives the HIL\_SENSORS and HIL\_GPS messages and FG receives the HIL\_ACTUATOR\_CONTROLS message with no problems. The acceleration information comes in HIL\_SENSORS right? If that information did not arrive, it would not respond with the message of HIL\_ACTUATOR\_CONTROLS ---
**Author:** ![JulianOes](https://discuss.px4.io/user_avatar/discuss.px4.io/julianoes/32/30_2.png) [@JulianOes](https://discuss.px4.io/u/JulianOes)\ **Post date:** [April 17, 2020, 10:58am UTC](https://discuss.px4.io/t/error-sitl/16255/4 "2020-04-17T10:58:16Z")
Ok, have you read this? [https://dev.px4.io/master/en/simulation/index.html](https://dev.px4.io/master/en/simulation/index.html) ---
**Author:** ![Juatarto](https://discuss.px4.io/letter_avatar_proxy/v4/letter/j/b9bd4f/32.png) [@Juatarto](https://discuss.px4.io/u/Juatarto)\ **Post date:** [April 17, 2020, 1:18pm UTC](https://discuss.px4.io/t/error-sitl/16255/5 "2020-04-17T13:18:50Z")
Yes, I have read it, but i dont see where the problem may be. ---
**Author:** ![Juatarto](https://discuss.px4.io/letter_avatar_proxy/v4/letter/j/b9bd4f/32.png) [@Juatarto](https://discuss.px4.io/u/Juatarto)\ **Post date:** [April 17, 2020, 4:06pm UTC](https://discuss.px4.io/t/error-sitl/16255/6 "2020-04-17T16:06:05Z")
From what I understand from the lockstep, PX4 does not calculate a new iteration of control actions until it receives a message from sensors with a different timestamp than the previous one, so simulations can be done at different times than the real one. I do not understand how there can be a timeout in this configuration ---
**Author:** ![JulianOes](https://discuss.px4.io/user_avatar/discuss.px4.io/julianoes/32/30_2.png) [@JulianOes](https://discuss.px4.io/u/JulianOes)\ **Post date:** [April 17, 2020, 5:56pm UTC](https://discuss.px4.io/t/error-sitl/16255/7 "2020-04-17T17:56:41Z")
Since you’re trying to get this going with FlightGear, have you seen this PR? > ---
**Author:** ![Juatarto](https://discuss.px4.io/letter_avatar_proxy/v4/letter/j/b9bd4f/32.png) [@Juatarto](https://discuss.px4.io/u/Juatarto)\ **Post date:** [April 17, 2020, 5:59pm UTC](https://discuss.px4.io/t/error-sitl/16255/8 "2020-04-17T17:59:11Z")
Yes, thank you, I have downloaded it and I have been seeing how it does it but it does not use the lockstep and for me it is very important since I am going to simulate many things at the same PC. So I would like to understand well how it works