A yellow flashing light indicates that a safety pre-check must be completed in order to properly arm and use the copter (note that this procedure is for your own safety).
To see what has caused Pre-Arm safety check failures.

  1. Connect your Flight Controller to Your Computer via the USB port.
  2. Start Mission Planner and select the “Connect” button on the upper right of the page.
  3. Turn on your radio transmitter and hold your throttle down and to the right (normal arming procedure).
  4. The first cause of the Pre-Arm Safety Check failure will be displayed in red on the HUD window.
  5. Address and correct each problem that is reported when you attempt to arm as above.
  6. When all problems have been corrected, you will see verification of “Arming” in the HUD window.
  7. You can then disconnect from your computer and have good assurance that arming will proceed normally.

To fix specific Pre-Arm check failures.

  • If Radio Calibration check fails re-do the Radio Calibration.
  • If Accelerometer Calibration check fails re-do the Accel Calibration.
  • If there is a Compass failure try to re-do the Compass’s Live Calibration.
  • If the Barometer check fails then your board likely has a hardware problem with the barometer.
  • If the GPS position check fails


  • Wait for your GPS’s hdop to drop below 2.0 before attempting to arm.You can make this more easily visible in the Mission Planner’s Flight Data screen’s Quick area.


  • Disable the Geofence in the Mission Planner’s Config/Tuning >> Geofence screen
  • Arm in Stabilize mode and switch to Loiter later (this is not recommended because a good GPS position is required for Loiter and the hdop is a good indication that the position is good)
  • increase the GPS_HDOP_GOOD parameter from 200 to 250 (this is also not recommended for the same reasons as the point above) If the board voltage check fails: If the board voltage check fails:
    8. If the board voltage check fails:
  • check the BEC being used to supply voltage to the APM is producing between 4.5 and 5.5 volts (the closer to 5V the better)
  • check if any peripherals that are being powered by the APM have too high a current draw.
    9. If Channel 7 was set to the same thing as Channel 8, change one of them using the Mission Planner’s Config/Tuning >> APM:Copter Pids screen

There is actually a way to deactivate these pre-arm safety checks (not recommended).
If you are confident that the pre-arm check failure is not a real problem you can disable the checks by:

  • Connecting your APM/PX4 to the mission planner
  • Go to Mission Planner’s Config/Tuning >> Standard Params screen
  • set the Arming Check drop-down to “Disabled” or if you are using AC3.1 (or higher) you can Skip the item that is causing the failure.
  • Push the “Write Params” button

Ideally however you should determine the cause of the pre-arm failure and if it can be resolved, return the Arming Check parameter back to “Enabled”
For more information about this please click here.