Timothy,
Any airplane I have flown with A/P has had either a VOR/LOC button and an APP button, or has had a VOR/LOC and a GS button. In the first instance, pressing APP the aircraft will NOT climb to capture the GS. In the second case, it’s a bit harder to say because I can’t remember the A/P model and it was a very very weird and defective airplane, however pressing GS in it would make it climb to intercept. I stress again that this was a very quirky airplane with lots of problems so can’t really suggest that this is normal.
Flying an ILS we use APP mode which as stated above will only hold the aircraft level until it intercepts.
flying an LNAV/VNAV approach we use LNAV and VNAV modes (naturally). Pressing VNAV when above the ‘glideslope’ will make the aircraft either descend, or fly level until the point at which it can descend to the FAF at idle thrust, at which it will start the descent as long as we have the platform altitude in. If we are already are below the ‘glideslope’ pressing VNAV will command level flight until intercept.
I can not (part from the quirky aircraft mentioned above) think of any approach or any normal autopilot approach modes which would cause a climb to intercept a glide path.
With an Stec 60-2 one can force the autopilot to track the GS by pressing the ALT button. The normal sequence is to intercept from below and to accomplish this with the aircraft in heading mode and altitude hold mode flying the vector to final, the pilot presses HDG and Nav simultaneously to fly the final vector heading heading until the intercept to capture the localizer or lateral course (NAV, HDG, and ALT should be annunciated). On intercept of the course, HDG will extinguish and APR will annunciate. , ALT will remain on until all the correct signals are present for a period of time and then GS will also annunciate to indicate it is armed. When the intercept point is reached, ALT will extinguish. If the conditions are not met for the GS to arm, and the pilot presses ALT (already engaged), this extinguishes ALT and turn on GS, the result being a sharp move towards the GS from above or below.
Autopilots other than the CIII that have GS tracking capability can also intercept from above or below the GS. If APR is engaged and the aircraft is directed thru the GS zero indication (from above to below or the more normal case from below to above), GS tracking will take over just past the cross over.
