not descending down the glide slope

APM Guest

Hi everyone,

I was flying from KLAS to KSFO, got to 18nm outside of SFO, was at 6,000 ft, 180knts with flaps at 30 in the default B747.

I had the nav 1 radio tuned in to runway 28R, with the course set at the right heading.

I turned the knob above the PFD from GPS to Nav and hit the approach button on the autopilot, and striaght away it knocked out the altitude ALT and climb rate buttons and the aircraft started climbing irractically.

I restarted and tried again, this time the alt and vr buttons stayed lit and the aircraft got in line with the runway but didn't decend down the glide slope. The alt button stayed lit at 6,000 ft right over 28R.

Does anyone have any ideas why the aircraft is not decending down the glide slope?? I tried it again on 28L and also at LAX (moving the aircraft on the world map) and the same thing happened!!! Can someone please help!



6 Responses

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

Read this:

It sounds as though you are too high. Your altitude should be half what it is currently for the ILS glideslope to be intercepted - an altitude of 2800ft is a good starting point. A lot higher than 3000ft and you'll encounter false glideslope lobes. Also, make sure you don't engage the AP before 12nm out or it won't lock on.

Pro Member First Officer
to_coolguys First Officer


I use the following procedure with PMDG 737.This is the procedure that i follow to get it down the glideslope.But in your case i found you to be at a much higher altitude..Normally the default ATC brings you down to 3700/2600 or 4600 ft.

1) As I am 20 nm away from the airport I am flying at 180 KIAS with 1 degree of flaps.I put in the appropriate frequency for the runway into the radio stack NAV1.Here I am still on A/P switched on and the speed controlled through Autothrottle.At this point I also put in the exact runway heading in the CRS i.e course selector.I hold this altitude with the ALT switched on

2) By the time I am 15 nm miles from the aiport I am on 170 KIAS with 10 degrees of flaps.

3) At this point generally the localiser symbol gets activated on the Attitude indicator and it starts moving.

4) Once it starts moving I press the APP for approach and also set the speed to 160 with 15 degress of flaps.

5) The autopilot aligns the aircraft to the runway.At this point I pull down the landing gear and arm the spoilers.I set the autobrake to 2.

6) Once aligned and stable,I reduced the speed to 150 KIAS with 20 degrees of flaps.

7) After some time the glideslope gets activated and starts moving downwards.As soon as it approaches the centre tha autopilot disables the ALT which is Altitude hold and starts following the glideslope

8 ) From here on as i start descending I set the speed to 145 with 20 degrees of flaps and then to 140 with 25 degrees and when I am about 1000 AGL i put it to 135KIAS and 30 degrees of flaps.

9) The autopilot follows the localizer and glideslope perfectly.

10) Around 100-200 ft AGL i disengage the autopilot and close the autothrottle and the manually land the aircraft.

11) When 50 ft above the runway I flare the aircraft to about 3-5 degrees and hurray I hit the centre line.

Now this is the procedure that i follow when I completely approach using the autopilot.It could vary from person to person and obviously the aircraft.I learnt it with the help of good and knowledgeable people on this forum and reading post .Also I did watch a video of PMDG 737 found on site and observed the config parameters for the aircraft as they were doing a landing.And it helped...Hope this helps you too... 🙂

APM Guest

ok thanks for all your help guys, I will try it out again tonight.

Hope it works cause I have to be up for work at 6AM Sad

Pro Member First Officer
to_coolguys First Officer

in a default 747 you would need to add 20 knots to all my speeds mentioned above as default 747 stalls at 135 knots.. 😞

APM Guest

hey guys

just wanted t let u know i followed your advice and landing perfectly at SFO, LAX, IAD and LGW!!

thanks again!!

Pro Member First Officer
to_coolguys First Officer

cool man. so you are on ur way to be a pilot.

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