Silly Question G/P vs G/S

[Ty53650 1]

I understand (I think) G/P is a mode of VNAV, but while on approach, no matter what I do it locks onto G/P and not G/S, and thence will not allow me to engage the 2nd autopilot for an autoland. Am I right to leave VNAV/LNAV on with APP mode armed when I'm turning to intercept the LOC? I managed a full autoland once but can't for the life of me get it to go again. I'm beyond sure it's pilot error, so if anyone can enlighten me It'd be much appreciated! Thanks

[Chaos81 110]

What approach are you having this problem on?

[Ty53650 1]

KGTF (Great Falls, MT) ILS 3, which is the same one that worked for me the ONE time

[usmc3073 3]

I was having this problem on an approach to KIAH it was picking up the back course and indicating BCRS on the PFD. I forget the specific PMDG option but it has something to do with fsx ils crs drift i think. I notice after I dial the CRS in that it changes to compensate for the drift I was on a CRS of like 087 and the drift ended up at like 289 degrees picking up the Back Course and then not allowing auto land. I found that if I either capture the VOR before it compensates for drift I am fine or I can just re dial the front course. That is what was causing it for me anyway... Guthrie Z

[Ty53650 1]

Hmm, I do recall having the course selector locked to the APR course the first time it worked, but this time I was still able to change the course. I have noticed that the app course on the PFD is different than the actually approach plate app CRS. Is that the reason I can't engage the other autopilot channel ya think?

[Tabs 2,790]

Guys, G/P (glidepath) is the Integrated Approach Navigation (IAN) pitch guidance mode. FAC (final approach course) is the roll guidance mode in IAN. This is the Boeing airliner equivalent of the WAAS LPV approach capability on the Garmin 430/530W units. You can use these modes to effectively make non-precision approaches fly as if they were ILSes. (higher minimums still per the charts, but the concept is the same) FAC is a computerized localizer and G/P is a computerized glideslope. If you press APP before you're actually recieving the glideslope radio signal it's going to engage G/P mode. You need to wait until you're actually receiving the full ILS signal before you press APP. If you're only getting the localizer, descend to the minimum altitude for the next fix on the approach and engage VOR/LOC only.

[Chaos81 110]

Ty, Just to confirm what Ryan said, I did a test with the approach you mentioned at KGTF and found that if I activated APP mode too far out, I got G/P indication like you mentioned. When I waited a bit, I got the G/S as expected. I suspect that's what you did differently when you were able to get the full autoland, you probably just waited a little longer to hit the APP button.

[Ty53650 1]

Excellent guys! Much appreciated, will be trying this out first thing tomorrow, boy I've got a long way to go before I feel completely comfortable in this baby, and that's the kind of simulations I like! Thanks again.