diydrones/ardupilot — pull request #1643 by samsonact (2014-11-29 09:22:19+00:00)
Title: PX4: Provide a way to enable px4io sbus1 output

Simplest way to turn on "px4io sbus1_out" for ArduPlane.

The other option is to add a new parameter and pass through to PX4 (I think it is just one ioctl). This would be a little more invasive I guess.