Hold on here, I had the impression (from flying simpler sims) that the "app" button could capture BOTH the localizer and the glideslope, in other words, I could just press the "app" button when I got close to intercepting the runway course and the plane would grab it (the horizontal course), and when it hit the glideslope from below, it would also grb the glideslope., If I read the above correctly, in this plane pressing the "app" button is not enough to grab both the horizontal and vertical guidance? If so, there should be a "warning" in the manual addressed to fans flying other models. I have also read that this plane, contrary to most, can grab the glideslope from above? Henri

Yes, the Approach button can capture both !! Fred.

. I have also read that this plane, contrary to most, can grab the glideslope from above?Henri

REALLY !! Out of curiosity, where did you read that ?? Geoff

I haven't looked in the FCOM yet but what is the logic behind arming VOR/LOC on approach, then the APP function on the AFDS?

I haven't looked in the FCOM yet but what is the logic behind arming VOR/LOC on approach, then the APP function on the AFDS?

VOR/LOC also lets you follow a VOR course !! APP doesn't !! Some pilots like to capture the localizer and then fly the glideslope manually.Don't ask me why !! Fred. Fred.

Don't ask me why !! Fred. Fred.

Why?Only kidding. I understand the logic. It does seem odd that if you're planning on shooting an ILS approach that this method of capturing on VOR/LOC then arming APP mode is the standard. I alway do it this way but never know why apart from it's an SOP

Why?Only kidding. I understand the logic. It does seem odd that if you're planning on shooting an ILS approach that this method of capturing on VOR/LOC then arming APP mode is the standard.I alway do it this way but never know why apart from it's an SOP

I am in the habit of presing VOR/LOC for localizer capture but could just press APP.In the NGX i try and fly VNAV all the way down to glideslope capture.So VOR/LOC knocks out LNAV and APP knocks out VNAV. Fred.

I believe, on Boeings, it is a user option to have the G/S capture with or without the LOC. So, if a company buys some planes from Boeing, leases a few from GE, merges with Airline ABC, etc. they'll have several different plane versions. So rather than have to remember which planes do what, you could write your SOP to cover the most conservative methods. That's one possible explanation. Another might be that the people who wrote the SOPs don't understand Boeings or just feel like making us press extra buttons. And yes, you can intercept the G/S from above. Your prissy Instrument Written Exam covers this many times, but the wings don't fall off if you intercept from above. ;)

REALLY !! Out of curiosity, where did you read that ?? Geoff

Hmmmm...Maybe in the manuals, maybe on this forum, who knows? Wish I could remember... henri

I've never heard of an auto-pilot that wouldn't capture the G/S from above. Just watch your descent rate and vertical bearing for a false G/S.

I haven't looked in the FCOM yet but what is the logic behind arming VOR/LOC on approach, then the APP function on the AFDS?

One reason would be to avoid a situation of capturing the glideslope when the localizer is either not present, or not yet captured. Doing so is potentially dangerous, as the aircraft will begin descending in APP mode once the glideslope is captured, but if it is not yet established on the localizer, there is no guarantee of being properly aligned with the runway centerline, and thus, having clearance from underlying terrain. (Picture an airport in a valley, with high terrain on either side - where the ILS is aligned with the center of the valley - a scenario that exists in many r/w approaches). One way to avoid this situation is by the option of configuring the autoflight system so that the aircraft will not capture the glideslope without a valid localizer being present. This option is enabled by default in the PMDG NGX, but can be disabled via the CDU PMDG Options menu. Even assuming that a given ILS system is working perfectly, the localizer ground transmitter radiates more power, and on a lower radio frequency than the glideslope transmitter. Therefore, it's possible to receive and capture the localizer well before a valid glideslope is received - (depending on how far out the aircraft is from the runway threshold at localizer intercept) By capturing the localizer in VOR/LOC mode, the pilot has the assurance that the aircraft will not commence a descent until such time as the glideslope is clearly being received well - at which time the APP button can be pressed so that the aircraft will begin descent when the G/S needle centers. Certainly no reason why the approach cannot be conducted in APP mode exclusively - as long as both LOC and G/S are being received - but the pilot has to monitor the PFD closely to make sure that G/S capture and ensuing descent does not occur before localizer capture.