Unexpected behavior on RC fail in Auto mode


Thanks to the open-source autopilot community, I was able to test drones to deliver goods between islands. However, I encountered a problem during my flight. Please find the details below, along with the attached log.


  • Flight Controller (FC): Pixhawk Orange
  • Firmware: Ardupilot (4.3.4)
  • Large Hexacopter
  • Companion computer: Jetson TX2, programmed by another company (not by me), used for LTE control and video stream for multiple drones. As far as I know, this companion computer and custom GCS generate fake RC signal for LTE control with no rc receiver(joystick).
  • Transmitter (TX), Receiver (RX): SIYI MK15 (RX connected to Pixhawk telemetry port, QGC running on MK15)
  • FS_OPTIONS: 15 (Continue if in Auto on RC failsafe, Continue if in Auto on GCS failsafe, Continue if in Guided on RC failsafe, Continue if landing on any failsafe). Both RC Failsafe and GCS Failsafe were turned on.

[Details of Flight]

  • Objective: Delivery with LTE between islands.
  • Traditional TX was on the destination island with another operator. Only joystick and LTE GCS were used for takeoff.


  • I was able to take off with only LTE. However, after flying out to sea, the LTE connection was lost. When the LTE reconnected, I found the copter was flying to waypoint #1 instead of continuing auto or RTL. This was a very strange situation. In auto mode, although failsafe was triggered, if it returns to auto mode, it should continue to next waypoint. However, it was heading to waypoint #1. I was able to reproduce this problem many times that day.
  • Before this day’s flight, during the experiment, only LTE with joystick flight was possible. There was no problem with no RC and LTE joystick flight. during experiment, I turned off RC or LTE, but nothing happend. but in actual flight there was problem.

[Timeline for the Log]

[11:08] Took off with the custom GCS’s joystick mode and set the copter to auto mode.

[11:09] Normal flight (to waypoint #2).

[11:10] Normal flight (to waypoint #3).

[11:11] Normal flight (to waypoint #4).

[11:11] Arrived at a poor LTE connection point. Turned off the custom GCS and turned it on again. The copter’s heading changed to the home position, which seemed to perform RTL. In the log, the copter was headed to “#1, #2” waypoint.

[11:11] After this happened, in the log, there was a message “Radio Failsafe - Continuing Auto.”

[11:11] Changed to loiter with LTE joystick to stop the copter.

[11:12] Performed “auto” flight again with custom GCS.

[11:12] LTE connections was lost again, and reconnected. so changed to loiter to stop the copter heading to waypoint #1. Didn’t do anything other than that. There should not be a brake mode, but there is a “brake” mode record in the log.

[11:13] Changed to loiter to go to the destination manually.

[11:14] Because it was heading to waypoint #1 if triggers auto, some waypoints were removed and uploaded again. (“Flight plan received” message in the log.)

[11:20] Arrived at the destination.

[11:21~] I have omitted to write the events that occurred after that time, as they are not relevant to this issue, I believe.
anyway, copter returned to take-off position successfully.

Today I performed experiment, but couldn’t regenerate this problem.

we turned off GCS and RC in the air with many configurations.

GCS maker said they debugged the GCS and there is no reason to return to waypoint #1.

it turned out that problem was because of my companion computer.