Telemetry Loss While Flying in Autonomous Mode

PX4 Autopilot
1

Hi everyone,

I recently experienced a crash with my custom-built fixed-wing aircraft (7.5 kg, high wing loading) while flying in autonomous Mission Mode.

The Incident: During the mission, the telemetry connection was lost. Since NAV_DLL_ACT was set to Hold Mode, the aircraft transitioned to Hold. Due to the energy management logic, the throttle was instantly cut to 0%. Given the aircraft’s weight and drag, it lost airspeed rapidly during the bank and stalled.

Proposed Solution: To prevent this from happening again, I am planning to apply the following parameter changes. Could you please verify if these changes are sufficient and safe for a heavy airframe?

  1. NAV_DLL_ACT → Disabled (Currently: Hold)
  • Logic: I want the aircraft to continue its mission even if the GCS link is lost, avoiding unnecessary mode transitions.
  1. FW_THR_MIN → 15% (Currently: 0%)
  • Logic: To ensure the motor never stops completely during descent or Hold modes, keeping airflow over control surfaces.
  1. FW_THR_SLEW_MAX → 0.2 (Currently: 0.00)
  • Logic: To prevent instant throttle cuts that destabilize the aircraft pitch.

My Question: Do you agree that these three changes are the correct solution to prevent a stall in this scenario? Are there any other “hidden” parameters I should check to ensure the throttle doesn’t drop unexpectedly?

Log File: https://review.px4.io/plot_app?log=0b3a9596-8e7b-40ac-b5eb-978261cfd616

Thanks for your advice.