Today I intercepted and tracked a programmed GPS leg, using the NAV mode on the 225 as is normal for GPS nav enroute.
Then I pressed APR. This is the first time I tried that in the 12 years since I got the plane.
Normally APR is used to intercept an ILS localiser, and that in turn sets up the autopilot’s “logic” to expect and intercept the glideslope.
It has however been suggested that APR in GPS mode makes the tracking tighter. So I tried it…
On the KFC225 display, “NAV” changes to “APR” and nothing else happens. Pressing NAV changes the “APR” back to “NAV”.
Then I tried intercepting and tracking the programmed leg, using first the usual NAV mode and then the APR mode.
No visible difference! I didn’t capture the GPS track but it was pretty obvious that the behaviour was as identical as one could tell. (The KLN94 was set to 1nm FS throughout).
So I don’t think the KFC225’s APR mode does anything different to its NAV mode, when tracking a GPS track. In most installations, this corresponds to the “NAV/GPS” switch (normally mounted somewhere in the panel) being set to “GPS”, and that drives a relay which connects the GPS’s deviation outputs to the autopilot. Otherwise, that relay connects the NAV1 radio’s deviation outputs to the autopilot.
