@astrojohn,
Only the Pixhawk has the capability to run the Extended Kalman Filter (EKF).
You can run the latest Arduplane firmware on your APM2.6 without out a problem.
I always use telemetry so that I can see how many sats have been acquired and the resulting HDOP. Then there is no issue as to when it is good to launch.
I don’t have telemetry? Isn’t that a load more weight and money? Not to meantion the ground part. Which I don’t have. If it was say £20 and 3g airbourne weight to add it then it might be worth it.
Not sure why plane code section to assign leds cannot be the same as copter software is a problem.