Glide slope problem

This is normal.

The GS in FS is designed to guide you to a TD rather far down the runway. If you do not have visual as you are passing over the threshold, you should not be landing there and certainly not depending on the GS to get you on the runway without visual.

However, if you accept that within 500 ft AGL of the runway, and acquiring visual you then ignore the GS and put it down, OR accept that relying on the GS will place you a considerable distance past threshold, then you will be able to cooperate with the intended design of the system in FS. That's the way it is.

-Pv-

I just flew that approach on ILS and the indicator was ok until I got to end of runway at about 40 ft AGL. Of course the TD point is not at the end of the runway as indicated with the arrows and can't land there. Then about 10 ft and at edge of TD the indicator suddenly shot up from being centered to moving up and pegging just as I touched down. Weird.

Then on taxi I saw a bunch of regular AI vehicles crossing in front of me on tarmac after I turned right off runway (maybe it's traffic going to the 'Speedway' racing track?). Also weird.

Chuck B

I just flew that approach on ILS and the indicator was ok until I got to end of runway at about 40 ft AGL. Of course the TD point is not at the end of the runway as indicated with the arrows and can't land there. Then about 10 ft and at edge of TD the indicator suddenly shot up from being centered to moving up and pegging just as I touched down. Weird.

 

Then on taxi I saw a bunch of regular AI vehicles crossing in front of me on tarmac after I turned right off runway (maybe it's traffic going to the 'Speedway' racing track?). Also weird.

Chuck B

I don't know if the issue is just with that runway. I will try some more landings with the jet. I did another landing at KBOS ( Boston Logan) with a Beechcraft Baron and things looked normal.

AIUI, in an ideal world all ILSs would be perfectly aligned with the runway, in all three pertinant ways - at the touchdown zone, at the correct (same) angle as the runway heading, and along the centreline. However in the real world this isn't true.

For example, have a go at flying into Nice (LFMN) runway 04R, or just take a look at its approach plate. Not only is the ILS displaced quite significantly to the right, its also 5 degrees off alignment.

Thus, once the ILS has got you "nearly" there, the last few hundred feet of the approach is visual and should be flown manually ie autopilot turned off. Also, regarding touch down zones, if you're landing a "small" aircraft" at a "long" runway (all things being relative), you may have plenty of excess runway available so you can continue a little way along to stabilise the approach/landing. In a bigger plane/shorter runway where the available landing distance is much closer to the required, there is a call for more precise flying since there is not so much of a margin for correction at the end (of the approach).

ILS Cat 3 is a more precise upgrade but as standard FSX doesn't support this etc

Each runway has 1 transmitter for glideslope. It is placed in the middle of the runway. And works in all directions. Not only pointing in the approach directions.

So, naturally, at the runway end at ground level, the glideslope is above you.

And the longer the (half) runway is, the higher it will be above you at that point.

The localiser is a transmitter at the far end of the runway. It points down the centerline. At a runway with two Ils direction approaches there will be two localiser transmitters. One at either end.

But only one glideslope transmitter.

This is exactly like it is in real life.

Google: ils localiser glideslope

And read the Wiki.

I realised "the middle" is not clear enough.

The glideslope transmitte is halfway down the length of the runway.

A little off to one side of the runway, in the grass.

You see it in fsx as a small black box with a small antenna on it.

AIUI, in an ideal world all ILSs would be perfectly aligned with the runway, in all three pertinant ways - at the touchdown zone, at the correct (same) angle as the runway heading, and along the centreline. However in the real world this isn't true.

 

For example, have a go at flying into Nice (LFMN) runway 04R, or just take a look at its approach plate. Not only is the ILS displaced quite significantly to the right, its also 5 degrees off alignment.

 

Thus, once the ILS has got you "nearly" there, the last few hundred feet of the approach is visual and should be flown manually ie autopilot turned off. Also, regarding touch down zones, if you're landing a "small" aircraft" at a "long" runway (all things being relative), you may have plenty of excess runway available so you can continue a little way along to stabilise the approach/landing. In a bigger plane/shorter runway where the available landing distance is much closer to the required, there is a call for more precise flying since there is not so much of a margin for correction at the end (of the approach).

 

ILS Cat 3 is a more precise upgrade but as standard FSX doesn't support this etc

I normally fly a jet manually as soon as I see the rwy under normal vfr conditions. I will do so even with visibility less than 1/4 mile. I like the challenge and have always been interested in difficult landings. That's why I pay so much attention to what the gs is telling me. I will need to compensate based on the level of accuracy of the gs taking into account the information given here.

I normally fly a jet manually as soon as I see the rwy under normal vfr conditions. I will do so even with visibility less than 1/4 mile. I like the challenge and have always been interested in difficult landings. That's why I pay so much attention to what the gs is telling me. I will need to compensate based on the level of accuracy of the gs taking into account the information given here.

I find that often the autopilot simply can't capture the ILS guidance well enough to usefully use it. Sure, if you're really careful you can set up the route before capturing the ILS, eg by intercepting it at 20 degrees or less, but often the phases before that simply aren't possible so if you capture it at too high an angle, there's an inevitible overshoot then "hunting" around side to side for the path. So, often this part is done manually for me. I'm not good enough yet to do it just off of the instruments, if I can visually see the runway and the plane is a nice one to fly and I'm used to it (still getting used to the bigger ones! I have just started really, so started with smaller planes) I can normally do as good or better a job than the autopilot. Once I'm manually on it, sometimes its handy to turn the autopilot back on (in approach mode) and let the autopilot do the trim corrections while I slow the plane down, get the gear down and get the flaps configured for landing.

You may already know, but I'll say just in case;

The glideslope is usually 5% angle.

(that is around 3 degrees)

The altitude vs distance relationship on that angle is around

300 foot down, for every mile forward. That's the miles on the dme.

So 3miles out, around 900ft,

2 miles out, 600 ft

1 mile out, 300 ft

Usually the Ils also shows you a DME indication.

Sometimes there is a ADF beacon near the runway end. Or a (short range) Terminal VOR close to the runway. Those can be used at airports without ILS also of course.

I realised "the middle" is not clear enough.

 

The glideslope transmitter is halfway down the length of the runway.

A little off to one side of the runway, in the grass.

 

You see it in fsx as a small black box with a small antenna on it.

"The middle" is a bit of a stretch.

You find them abeam of the touchdown bars.

And they look like this...

peace,

the Bean

You may already know, but I'll say just in case;

The glideslope is usually 5% angle.

(that is around 3 degrees)

 

The altitude vs distance relationship on that angle is around

300 foot down, for every mile forward. That's the miles on the dme.

So 3miles out, around 900ft,

2 miles out, 600 ft

1 mile out, 300 ft

 

Usually the Ils also shows you a DME indication.

Sometimes there is a ADF beacon near the runway end. Or a (short range) Terminal VOR close to the runway. Those can be used at airports without ILS also of course.

I was aware of the angle but not the distance info. That's useful. Thanks.

I find that often the autopilot simply can't capture the ILS guidance well enough to usefully use it. Sure, if you're really careful you can set up the route before capturing the ILS, eg by intercepting it at 20 degrees or less, but often the phases before that simply aren't possible so if you capture it at too high an angle, there's an inevitible overshoot then "hunting" around side to side for the path. So, often this part is done manually for me. I'm not good enough yet to do it just off of the instruments, if I can visually see the runway and the plane is a nice one to fly and I'm used to it (still getting used to the bigger ones! I have just started really, so started with smaller planes) I can normally do as good or better a job than the autopilot. Once I'm manually on it, sometimes its handy to turn the autopilot back on (in approach mode) and let the autopilot do the trim corrections while I slow the plane down, get the gear down and get the flaps configured for landing.

I flew props for years before getting into jets. Props are still my favorite. I love airport hopping to little remote airports in a Cessna using vor navigation and low altitutde enroute charts. Lots of fun.

I find that often the autopilot simply can't capture the ILS guidance well enough to usefully use it. Sure, if you're really careful you can set up the route before capturing the ILS, eg by intercepting it at 20 degrees or less, but often the phases before that simply aren't possible so if you capture it at too high an angle, there's an inevitible overshoot then "hunting" around side to side for the path. .

That's probably with a default plane though.. They don't fly the localizer too well, and

do act as you describe. But the better planes don't have that problem.

IE: the 737NGX can handle even a 90 degree turn to the localizer no problem at all.

Once I get to minimums for a visual, say 200 ft or whatever, I'm not watching the

glideslope much anymore past that point.

I see peculiar behavior of the glideslope at quite a few of the artificial airports.

I don't worry much about it. By the time I start getting close, I'm usually watching the

VASI more than the glideslope if visual. In fact, if the glideslope says one thing, but

the VASI says something else, I usually let the VASI lights rule over the radio signal.

The lights will never lie, assuming no bulbs are out.. lol. :rolleyes:

 

I see peculiar behavior of the glideslope at quite a few of the artificial airports.

I don't worry much about it. By the time I start getting close, I'm usually watching the

VASI more than the glideslope if visual. In fact, if the glideslope says one thing, but

the VASI says something else, I usually let the VASI lights rule over the radio signal.

The lights will never lie, assuming no bulbs are out.. lol. :rolleyes:

Indeed. A lot of the approach charts have text something like "ILS glideslope doesn't coincide with VASI lights" on them. I'm not sure but I imagine if runway length was critical, a pilot would need to look at where the ILS glideslope took you vs where the lights are situated vs where the marked touchdown zone is on the runway, and late into the descent ignore either or both to aim for the touchdown zone and get the max runway length available.

AIUI, in an ideal world all ILSs would be perfectly aligned with the runway, in all three pertinant ways - at the touchdown zone, at the correct (same) angle as the runway heading, and along the centreline. However in the real world this isn't true.

 

For example, have a go at flying into Nice (LFMN) runway 04R, or just take a look at its approach plate. Not only is the ILS displaced quite significantly to the right, its also 5 degrees off alignment.

 

Thus, once the ILS has got you "nearly" there, the last few hundred feet of the approach is visual and should be flown manually ie autopilot turned off. Also, regarding touch down zones, if you're landing a "small" aircraft" at a "long" runway (all things being relative), you may have plenty of excess runway available so you can continue a little way along to stabilise the approach/landing. In a bigger plane/shorter runway where the available landing distance is much closer to the required, there is a call for more precise flying since there is not so much of a margin for correction at the end (of the approach).

 

ILS Cat 3 is a more precise upgrade but as standard FSX doesn't support this etc

Here's an example of how the ILS is misaligned with a runway, albeit horizontally. The visual suggests the runway centreline is to the left, while the ILS indicator suggests its way over to the right. I am sure if I keep searching, I can find an example where the glideslope is displaced too, but its probably much less common since it would be quite unnerving if so.

Nice shot paul_c2,

This illustrates the issue very well. Though I've seen instances where the ILS is even more misaligned than you show.

I'm a firm believer that ILS is not a usable Auto Landing System. I use both hands and both feet during the last parts of every final.

Misaligned sounds like it is an fsx error, it is not. An offset ils is used at those airports in the real world as well. This is to avoid terrain or other obstacles, or for noise abatement.

The ils signal is intended to help you descend (through cloud) to decision height only. Then you are supposed to take manual control and land.

You are only allowed to go below decision height if you can positively identify the runway at that time and with that confirm you are in the correct position to land from.

Respecting that its horizontal (not glideslope), I Google'd around and found this interesting thread:

http://www.pprune.org/tech-log/10442-runway-alignment-ils-approaches.html

I knew Isle of Man was a Special Airport Qualification, but not exactly why - now I do!

Nice shot paul_c2,

 

I'm a firm believer that ILS is not a usable Auto Landing System. I use both hands and both feet during the last parts of every final.

Only certain ILS approaches will be usable for autoland in the real world.

Of course, in the sim, any ILS which is properly aligned can be used for an autoland,

but that sure won't be the case in the real world.

Autolands are actually not that common overall. But will depend on the company, how

much nasty wx they fly in, etc..

As an artificial SWA buoy, I never do autolands. The HGS is used to hand fly catII-III

approaches instead.

I usually fly the BBJ's much the same as I rig them up pretty much the same as a SWA

jet with HGS, etc.

The only time I do an autoland is if I just want to do one for giggles just to watch

the machine fly itself. Maybe one out of every 100 or so..

I had a friend of mine that was an A&P. For a while he was working on choppers

at the Chino, Ca airport. He told me a story about one GA pilot who tried to use the

ILS all the way to the ground in low viz one night. It didn't end well. :(

A glide path transmitter essentially sets up a conical surface for you to follow, with the tip at the foot of the GP mast. If you are on this cone, your GP needle will be centered.

As has previously been stated, each ILS has a GP transmitter located to the side of the touch down zone - and therein lies the crux of the matter.

When you are on the extended runway centerline approaching the runway, visualize following a vertical "cut" through this cone*, just to one side of the tip. When far out, it will for all practical purposes be a straight line aimed at the touchdown zone. When you get close to the GP mast, the GP signal will curve upwards, or 'flare'. It will never really touch the runway surface but level off at a height above the runway at the touchdown zone. To actually fly the GP down to the ground, you'd have to fly straight at the GP transmitter mast and hit the ground at the base of the mast rather than on the runway.

In other words, if you fly a straight path to the touch down zone, the GP needle will indicate 'fly up' (rise) as you get near the TDZ. If this is what it does in FS, FS is Doing It Right™.

*) Those with a background in mathematics will recognize this as a hyperbola

(Various tricks are used to improve the signal beyond the basic geometry described here, but that's beyond the scope of this discussion I think.)