Confusion about the IO failover to servo power/manual control

While reading through the Pixhawk 2 documentation on the ProfiCNC website I noticed an interesting statement on page 6 under “PWM Outputs” and page 8 under “Servo Power” and “Servo rail”. It states that in the event that the two main power sources fail, manual control should be obtained with just the servo rail being powered for plane configurations.

My current setup is running Arduplane and an SBus input to the Pixhawk. When both the Power 1 and Power 2 blocks are removed I can see the carrier board is still powered through the servo rail, however I no longer have control of the servos on the Main Out channels as is suggested by the documentation. Has anybody else ever successfully tested this or am I misunderstanding what is being said? Any insight would be greatly appreciated.

Attached is the link to the Pixhawk2 specifications pdf.

Do you have pass through set up? Look it up on

Can you give me a little more direction? I’m still kind of new to the Pixhawk community and am having trouble finding information on pass through on the supplied website.

@philip Bump for assistance. Method for testing IO co-processor on FMU failure on the hardware (CubeBlack).