High glideslope interception altitude
 

Is it possible to start autopilot coupled ILS approach from altitude more than 2500 ft with non-ready data from radio altimeter (RA out of range)?

Thanks.

yep...
though the approach might have some limitations...
ie normal GS range is 10 nm unless more is required...

I mean - Is an APP mode of AP operational while rad alt out of range?
(For example - with Collins ALT-4000 radio altimeter)

Nagative the AP will continue searching (flashing) until signal is obtained , yes if you keep the AP on engage APP and line it up it will continue the app as soon as intercept has occured

false glideslope
 

Automation will pick up the glide, but with no valid RA cat2 and cat3 is not possible.as you fly along and once RA input gets validated it will upgrade to autoland capability. caution watch out for false glideslope intercept !!!

I have seen many guys try this and not successfully. KLAX has a long drawn out arrival that intercepts the G/S about 25 miles out, if you want to. But, using the VNAV profile works much better. The signal is too erratic beyond 10 nm.

Gf

Of course it all depends on the aircraft you are speaking of. Normally LOC allways captures first and will do so as long as it is within the beam, having said beam think of it as a weaker but wider signal at distance from the ground equiptment. GS capture will occur as the same, just expect more hunting at further distance.

Aircraft are usually set up to adjust gain to finer tolerances as you get closer to the threshold, this is usually done first for the loc on gs cap, sometimes marker beacons trigger stages and RA.

RA input to most autoland systems is not much more than a valid at altitudes but the aircraft w/o it will still fly the ils to the ground, just will not flare in it's absence.

Really any ILS coupled A/P is more or less cat III w/o flare.

On the 744 GS will capture as long as LOC is captured. On the 742 in ILS mode, some will capture GS even before LOC; again, RadAlt altitude is not considered.