Following the GS

[cessna_driver2]

What happens if the GS is NOTAMed out of service or you don't pick it up on the receiver? Just use the VASI/PAPI?

-mini

Shoot it as a localizer approach?

 

[minitour]

Shoot it as a localizer approach?

well....yeah of course if there are LOC only minimums on the approach plate....but we were referring to a visual

-mini

 

[Crosswind79]

I'll stay on it to DH....After DH, the glide slope is not accurate under a category one approach - only category II and III

 

[Dr Pokenhiemer]

Crosswind--got slap your instructor! Really hard!! If you look at the ILS approaches to 36R at CLT, you'll see that the ILS 36R as well as the CAT II and CAT III ILS's ALL have the SAME localizer freq. of 108.9. (I'm not going to say, "That being said" because I think it's stupid and overused.) Now, if the localizer is not accurate below DH, how can these airliners follow it all the way down with an RVR of 600 or less or do an auto-land? The pilots have to shoot 3 CAT III approaches in order to be quailified to do this on their own. (I think.) The localizer IS accurate, your average instrument rated pilot ISN'T accurate enough. It's like a VOR--the closer you get to the station the less correction it takes. Try it on your Microsoft FlightSim. you'll see what I'm talking about.

 

[avbug]

Aaah, microsoft sim. The definitive reality experience. Not.

The question has been raised as to weather the ILS is accurate below minimums (200' has been given, suggesting category 1). It's not an issue of weather or not the ILS is accurate, but weather it's flight checked.

A category 1 ILS is not flight checked below minimums, and use of the glide slope below minimums is not authorized for vertical guidance. You can certainly reference it, but you cannot rely on it.

If that ILS has Cat II or III minimums published for it, then it's flight checked right to those minimums. In that case, the glide slope will be approved and has been regularly proven to minimums, including touchdown for Cat III with autoland, but the restriction then becomes one of pilot and aircraft, rather than the approach system.

It may be that the pilot is not approved for category II or III approaches, even though those minimums are published for the runway. The pilot may not descend below the Cat I minimums in this case, using the electronic glideslope for guidance, even though other minimums are published and the glideslop has been flight checked lower.

Bear in mind that many ILS don't go to 200'...many are higher. In these cases, the glide slope has been flight checked to the published minimums, and you may not rely on it below those altitudes.

In other cases, such as the Reno ILS (19R, I believe...foggy brain this AM), the approach goes to 1100 HAT. That's the decision height. However, approved operators are individually permitted the Silver ILS, which permits a 200' DH. In this case, the approach has been flight checked to 200', and the higher restriction and minimums are published in general due to missed approach and obstacle criteria. The silver minimums are assigned after an operator is able to demonstrate the ability to meet the higher climb gradient criteria from the lower DH.

To make a long story short, the issue of weather the glideslope is useable or reliable or accurate below minimums is superfluous. Who cares? It should be reliable, but may not be...but it's not legal for use below minimums, except as a reference. Further, it's not flight checked below minimums; you have no gaurantee.

Personally, I stay with the glide slope to touchdown, unless a visual indicator intervenes. If I'm on glideslope below minimums, visually landing and I start to get a low indication on the visual indicators, I'll reduce the rate of descent slightly to remain above the visual indicators, touch down a hair farther, and everybody is happy. When staying with the glideslop, I recognize that below minimums, I'm visual, and that I'm relying on my visual perception of the approach, and not the glideslope. It's now a reference, only.

 

[philo beddoe]

As far as autoland goes, I had been told that the last 50 or 100 feet is not done on the GS but uses radar altitude and computed descent rates. This is because the last 50ft of the GS can do some funny stuff.

 

[typhoonpilot]

This is because the last 50ft of the GS can do some funny stuff.

Actually, the aircraft needs to flare so it will usually enter a flare manuever at approximately 50 feet. Following the GS down all the way without flaring might be what causes funny stuff to happen .

TP

 

[FarginDooshbahg]

Dr. Pokenputz needs to pay attention. This thread is about the GLIDESLOPE. You keep referencing the LOCALIZER. Maybe if you put down the MS Flight Sim long enough and read a book, you will understand the difference.

 

[minitour]

be nice guys...

sheesh...I was curious about a VISUAL approach and if you reference or "follow" the GS on that...

no need to get mean with each other...

-mini

 

[Dr Pokenhiemer]

DOOSH,

I WAS talking about G/S. Last time I checked, I dial up the localizer freq. and automatically get a G/S signal also. The post was about the G/S being accurate below DH. I haven't seen MS SIM in several years, just using that as an example before this young gun goes out and tries an IFR ILS to the runway in a real plane just because it CAN be done.

 

[Crosswind79]

Slap the instructor...hmmm - I'll stick with what I was taught, what I currently teach, Avbug, and almost everyone else on this thread EXCEPT for Dr. Know-Nothing....Cat I ILS is not certified down to the runway - thats why the DH is usually 200 feet above the runway ( higher in places like reno and tahoe )...If it was certified to the runway it would be a CAT IIIa or higher. Most of the people on this board know what they are talking about...As for the microsoft pilots, put down the joystick and read 1-1-9 of the AIM. Cat I is NOT usable to the runway for a number of reasons such as local anomalies, glide slope antena location, and aircraft siz and TCH.


There's the computer flying, and then the real world flying.....

 

[Dr Pokenhiemer]

I'll stay on it to DH....After DH, the glide slope is not accurate under a category one approach - only category II and III

I think you missed my point. I was trying to show you that it's the same GS for a CAT III approach as it is for a normal ILS. The only difference is YOUR certification or authorization to use CAT II or III. I believe you said the GS is not accurate below DH."

 

[Crosswind79]

I did say that its not acurate below DH...


ON A CATEGORY I APPROACH.....

If your shooting a CAT II or CAT III then the wx is probably pretty crappy in which case your going to follow the glide slope down to alert height or to the runway, depending on the type of approach your using. But if its a CAT I approach fly it to the DH and don't rely on anything below DH.

 

[avbug]

And said so incorrectly.

Is the glideslope inaccurate for a category I approach below DH? Almost certainly, yes. That, however, is irrelevant. It is not legal for use. The glideslope isn't flight checked nor approved for use below DH.

It's not a matter of accuracy. In most cases, it certainly is. However, it's a matter of legality; the GS isn't approved for use below DH. You can use it as a supplement to visual guidance beyond that point, and should remain at least above it until you have acquired visual vertical guidance.

 

[side stick-n]

Gotta chime in here. If it is not legal to use the GS below 200' on a CAT I approach, then please explain how it can be legal to continue below minimums to 100' above the TDZ with only the approach light system in sight. Uh, what do you plan to use for vertical guidance between 200' and 100'?