I haven’t found any discussions of how people have set up their tx. For instance, starting out and being new to the apm 2.5 and ardupilot, I would like some feed back of how users have set up functions of their radios vs apm’s control. Does apm prefer to have full control of full rate or does apm bypass d/r? I would think that it would be preferable to have flight mode switch not change the actual throws of the plane much at all but using the 3 pos sw just to change out of manual and into diff apm modes? Remember, I’m a new user and want to get my plane in the air and start with basic things but could really use some knowledge. I have a DX7 tx and using a 6ch rx but having trouble with my plane setup when apm is connected. I have my ale’s setup using two ch’s and i had flaps working using the aux sw on tx (ch 5), so my 3 pos sw isn’t showing up anywhere? Missing out on some great weather 
Hi Kevin,
For the APM you definitely need to assign a 3 position switch to an available receiver channel for mode select.
The Spektrum will allow you to select which receiver channel it gets out put on and you need to connect that receiver channel to channel 8 of the input channels on the APM.
Normally you would have the first 4 channels for your rudder, elevator, ailerons and throttle.
And that plus mode is 5 channels on a 6 channel receiver you have one channel left over (for you flaps I guess), but not 2.
if you need another channel for something else you are going to need a 7 channel receiver.
This is what I installed in my DX7 to get a six position switch. Simply replace the rotary pot switch with this switch. Works well and is easy to install. (UNIVERSAL Mode switch 6 POSITIONS - ArduCopter ArduPilot - READYMAD E-bay item number 110938433765)