A critical issue has been discovered with the FrSky SPort Passthrough telemetry feature (i.e. SERIALx_PROTOCOL = 10) in Copter-4.0.0, Plane-4.0.2 (or 4.0.0 or 4.0.1) and Rover-4.0.0 which can lead to an in-air lockup and crash. The issue is a race condition meaning that while apparently rare it is difficult to say when it might occur.
This issue only affects FrSky SPort Passthrough telemetry users who are on ArduPilot’s 4.0.x releases. This does not affect Copter-3.6.x, Plane-3.9.x or Rover-3.5.x users.
We strongly recommend 4.0.x users disable the FrSky SPort Passthrough telemetry feature by changing the SERIALx_PROTOCOL parameter from “10” to “0” until a fix is released.
Thanks for your patience and support!