747 Autoland below glidesope.

[Guest chris493]

Hi all,Once again sorry for my HUGE mistake and I hope we can get along.Anyway, I've noticed that when I'm autolanding the 747 at any airport I could be at 2000 ft for the start of the approach and select approach hold and the aircraft would start descending.Then the "Glidescope" callout would be heard for about 5 seconds and then it would go silent for the rest of the approach yet it shows I am bang on glidescope from the bars beside the Flight Director and on the approach page on the ND(cant remember what they're called-help me out).I would be using autothrottle at about 150-170 with flaps 30 (depending on gross weight) and on a clear day.Any help will be greatly appreciated.Thanks ChrisP.S:Here's some points to help you out:- 1-I am tuned to the correct ILS freq. and heading. 2-I am using autothrottle (150-170 knots) 3-Weather is mainly clear (usually) 4-Gross weight not over the maximum landing weight. 5-I am using flaps 30 6-I only tried it at WMKK, EGLL, EGKK, LIMC and LIRF all of which I have add-on scenery for. (Heathrow Pro and Gatwick Extreme-UK2000 (payware version), Project KLIA V2 (freeware) and ISD Projects LIMC and LIRF) 7-Rounding up no.6 no default scenery tested. 8-Aircraft still lands at roughly the touchdown zone markers. 9-Touchdown Zone elevation is correct.So basically it always takes a low (sometimes very low) approach.

[craig_read 43]

Hi Chris,Not sure what you mean here.. As I approach the runway for an ILS landing, first obviously the PFD lights up with the ILS vertical and horizontal magenta markers... Usually for me it's LOC on the MCP as I approach the track to the runway until I am established, and then when given permission to approach and descend with the ILS I set APP on the MCP.. APP is usually set before the vertical marker passes through the centre point (where it should stay on an ILS landing till flare), as it passes the aircraft will then pitch down and I set my missed approach altitude.. If you are setting the APP too late, perhaps your warning is an indication you are not descending at all and yet the glideslope is falling below you? This would explain the 5 seconds or so warnings to have.. as the aircraft pitches down dramatically and attempts to get the G/S back.. It also might explain any strange behaviour on it's way down.. the A/P can be funny in MSFS sometimes.. I've seen some very strange effects on other aircraft too..For me.. if the glideslope is below me.. I take control and manually attempt to get the aircraft back on the glideslope.. once close I re-engage the a/p for an autoland if I want to... I've found that sometimes the A/P (and not just in PMDG) can be a bit funny and bob about a bit.. pitching up.. down.. up.. down when attempting to follow a path.. this usually helps the plane on it's way..BTW.. 170 knots is high for an approach speed? The weight must be quite significant.. Typically on circuits I'm below 160 knots for landings I'm not sure what weight you're using.. sounds high to me.. could be wrong though..Not sure if that helps or not..CheersCraig

[michal 44]

>Then the "Glidescope" callout would be heard for about 5>seconds and then it would go silent for the rest of the>approach yet it shows I am bang on glidescope from the barsUnless you see "GS" in green annunciated on the PFD vertical mode indicator your are **not** flying a glideslope. So pay attention to what PFD is telling you.But regarding your question I have hard time understanding whhat is this "low approach" and how do you determine it is really low.

[rgamurot 1]

If you mean the aural glideslope warning, then this does mean you are below the glidepath. This is the only time this audio warning sounds. I've also never heard it farther than maybe 2 miles out so it may only happen close in. But then again I know I'm too low; I'm hand flying at that point! As far as when I fly a CAT3, I don't recall hearing any audio warning unless something goes wrong.Anyway, there is a G/S INHIBIT button on the MISC panel that will prevent the warning from sounding. As far as low, do you mean that the PAPI is showing 3 red and 1 white yet your indications show you are on the glidepath, or is it something else?Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png

[Guest chris493]

Yes the PAPI is showing 2 red and 2 white to start with then it goes to 3 red and 1 white.

[rgamurot 1]

I remember something about the ILS receiver being mounted on the tail which is high above the aircraf, of course. This would cause the aircraft to think it's correct but the PAPI to think you're a touch low. As you flare, the tail is blocked by the nose and the receivers in the nose (wheel well I think) take over and are now high off the ground themselves. Once again, I'm not 100% sure if this is the case in real life or if PMDG modelled this. But it would make sense. Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png

[Qavion 19]

"I remember something about the ILS receiver being mounted on the tail which is high above the aircraf, of course. This would cause the aircraft to think it's correct but the PAPI to think you're a touch low. As you flare, the tail is blocked by the nose and the receivers in the nose (wheel well I think) take over and are now high off the ground themselves."Actually, the 744 glideslope antennae are mounted behind the nose radome and on the nose gear (small) doors (You were perhaps thinking of the localiser antennae which switch between the tail and the nose?).So... when the gear goes down, the glideslope antenna are switched from the nose to another set of antenna mounted on the nose gear doors (even lower). This means that whilst the aircraft is tracking the glidepath nicely, the flight crew are 20~30 feet higher than the antenna, so you may see more WHITE than red in real life.However, the PMDG 744, for reasons unknown to me, is tracking low (in Chris' scenario) .Rgds.Q>

[Guest chris493]

Thanks that eplains everything

[Guest shogun007]

Just to add to QAVION's reply here is what the Boeing 744 Maintenance Manual has about it. If it's a bit too technical I apologise but there may be some of you who will appreciate it.Regards Steve PowerS/O 744Qantas 34.31 − INSTRUMENT LANDING SYSTEM − INTRODUCTION B744 − RADIO BOOK 3 INSTRUMENT LANDING SYSTEMGeneral DescriptionThe ILS receiver calculates vertical deviation from the G/S beam andhorizontal deviation from the LOC beam. Interfacing systems use thecomputed data from the ILS to aid in the precision navigation of theairplane.There are three instrument landing systems on the airplane, a left (L),center © and right ®. Each ILS consists of:

[Qavion 19]

"There are three instrument landing systems on the airplane, a left (L),center © and right ®. Each ILS consists of:

[Guest shogun007]

Thanks for the updated info Qavion