ILS landings with autopilot problem

[baldo]

I seem to be having problem with altitude when trying to let the autopilot follow the glideslope when flying the heavies. I hit the Approach button just outside the glideslope flying at about 180 KIAS at around 2500 to 3000 ft above runway alt. or whatever altitude ATC directs me to. The Heading light goes out first and the plane turns perfectly to intercept the runway. But then when the Altitude light goes out the plane starts dropping out of the sky and crashes way short of the runway. The strange thing is this only happes about half the time, I can refly the same flight moments later with the same exact speed and approach and it's fine.

Any thoughts for a beginner flight simmer?

Gary

[Bart]

Numerous posts on this subject...search "ILS Landing" for starters.

Default 747 a/c don't perform well when it comes to GS. Several posters have offered mods to the aircraft.cfg file to help with this problem. Downloaded 3rd party 747's are much better...POSKY for example. Even so, with a full load of fuel on board, you'll need more speed than 180 kts to maintain the initial reaction to the GS. On a full load of fuel, I usually intercept the localizer at about 210 with say 5° flaps. I also intercept the GS with this configuration as well and once established...then I reduce speed, lower flaps and gear accordingly in the approach.

Tom

[psolk1]

The speed is the key factor. If I try to slow down to 180 before the glideslope intercept, I will usaully fall short as well. I try to maintain my speed until the G/S has been captured and then slow down and hit the flaps and gear.

[baldo]

Thanks for the responses. I did do a search and have read many of the other posts. I haven't tried the 747, the problems I'm having are with the 737 and 777. In many of the other posts they suggest intercepting the G/S at 180, that was the reason I was flying at that speed. But it does seem to happen with a short flight which would mean a full load of fuel.

I will try a faster approach speed and see what happens.

Thanks

[doncarlos]

Sounds like you have way too much fuel on board...at approach you should only have enough left to reach your alternate + 45 min

Also, in my opinion too fast ... try less fuel, slow down to
160 - 170 and capture from below ....but it is a known issue in
02.


doncarlos

[cascadesss]

I agree with doncarlos.

You are carrying way too much speed and fuel. I usually intercept the localizer at 15-20 miles out with a speed of around 160, then slow to 140 (flaps at 20) with less than 25% fuel. When the aircraft intercepts the glide slope (at around 8 miles out), I set flaps to 30 degrees. It works every time


Rick - KPDX - Private Pilot
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[baldo]

OK, I guess there's 2 schools of thought here trying to decide on speed. But it does seem everyone agrees that it's difficult with too much fuel. When you plan a flight does it aadjust your fuel accordingly based on the distance of your flight or do you always get full tanks?

Gary

[Bart]

I always get full tanks on a new flight....my understanding is that its up to us, the pilots, to adjust the fuel based on what the flight plan calls for. I know FSNav gives an estimation and there are several fuel calculators out there as well.

I don't disagree with the lower speed approach posted above, but my only point was IF you have a full fuel load, don't expect to be able to intercept the GS and maintain it at those low speeds. I was merely offering a solution that works for me in a 747 WITH a full fuel load.

Do a search for the following fuel calculators...and take your pick.

B747Fuel.zip
Fucalc2k.zip Excel based calculator
Fuel11.zip

Note they all produce different quantities as they all seem to use different assumptions.

Tom