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View Full Version : Faf?


BEWELCH
12-01-2006, 02:42 PM
Does The Ils Have A Faf? If It Does How Can You Identify It If The Mm And Glide Slope Is Out??


Pilotpip
12-01-2006, 02:55 PM
If the glide slope is out you're not dealing with an ILS approach.

TonyC
12-01-2006, 02:55 PM
Don't you remember the thread you started a little over 2 weeks ago?

http://www.airlinepilotforums.com/showthread.php?t=6934&highlight=FAF







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AVIVIII
12-03-2006, 02:59 PM
Does The Ils Have A Faf? If It Does How Can You Identify It If The Mm And Glide Slope Is Out??

I read your other post and understand why you still have questions....


All approaches have a Final Approach Fix (or FAF) which can be identified in any number of ways depending on the particular approach. It could be defined by an Outer-Marker (OM) it could be a co-located outer marker (LOM), a radar fix, an intersection, a GPS fix, a DME fix, an NDB, a VOR, etc. Middle Marker (MM) has absolutely nothing to do with it though.

If you are looking at the plate for an ILS approach (precision approach), check out the profile view. You will see a lightning bolt in there somewhere. That lightning bolt is showing you minimum decent prior to crossing the outer marker if you have not intercepted the glide slope or minimum glide slope intercept altitude. The FAF is usually marked by a Maltese cross on the profile view, however, some ILS procedures do not show the Maltese cross, just the lightning bolt. The FAF is defined on the plate usually by one of the methods that I mentioned above. The point of having a FAF on an ILS doesn't go to much further than a place to start your time for the missed (in case you loose the glide slope) and a convenient place to put the gear down (its more than that, but for simplicity's sake...).

Now, about the glide slope. If you are cleared for the approach, have course guidance with the localizer and you are above the minimum altitude for that portion of the procedure, you can intercept the glide slope and start tracking it down, even if you are 10 miles out at 6000 feet. If none of the things that I mentioned earlier are working or you are unable to identify that particular point, there is one more way to find it. Looking at the profile view of the plate again, you will find that where the glide slope intersects the FAF, there is a little number there. If you are flying dead-nuts on the glide slope, when you descend through that altitude, you have reached your final approach fix.

If you are flying an ILS procedure and the Glide slope is INOP, then the procedure just became a non-precision approach, more specifically, a localizer only approach.

As far as I can tell, this is the scenario that you are presenting: You are setting up for an ILS approach with the glide slope INOP and the outer marker OTS and you are trying to define the FAF. You have a couple options. First, pick another approach. You either don't have the equipment to receive all of the appropriate information or the ground equipment is malfunctioning. If that approach is your only choice, see if ATC can call the FAF for you. You also might be able to find a cross radial from a near-by VOR. It may not be depicted on your plate, you might find it on the low chart, or as part of a different approach, but as long as it is the same fix, the numbers will work.

I hope that all of this helped!

TonyC
12-03-2006, 04:31 PM
The above posts contains generalizations that are not universally correct.


BEWELCH, do you have a particular approach you're interested in?



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AVIVIII
12-03-2006, 05:42 PM
The above posts contains generalizations that are not universally correct.
.

Like What? Besides the part where I said "for simplicity's sake..."

And I'm going to guess at your response: "There is no FAF, per se, on an ILS Approach."

The point of the post was geared toward the question. The scenario is that there is not a glideslope (lightning bolt and GS intercept are no longer factors) and there was no OM. And we are trying to identify a point in space, namely the point that lets us descend.

The other thing is that maybe people want to have a back-up plan. I don't know about anyone else, but I time all of my ILS approaches from the FAF (even if it is just for non-precision) just in case I lose my glide slope. If I am FAF inbound and I lose my GS, I'm not going to go around, I switch gears to a LOC approach. Its the same procedure with new mins. If you are picking up ice like a bad habit or trying to beat WX or any other situation which is not conducive to a do-over, you are going to want a back up.

TonyC
12-03-2006, 08:01 PM
The above posts contains generalizations that are not universally correct.




Like What?






All approaches have a Final Approach Fix (or FAF) which can be identified in any number of ways depending on the particular approach.



Not true.

Here's one example of an approach that has no FAF:

FAA Instrument Flying Handbook (Chapters 8-11) (http://www.faa.gov/library/manuals/aviation/instrument_flying_handbook/media/faa-h-8083-15-2.pdf)

Figure 8-11. More IAP profile view features on page 8-22 (Page 22 of 118 in the PDF Document). This figure shows various configurations of approach procedures. The third example from the top is a classic procedure turn where a VORTAC serves as both the Initial Approach Fix and the Missed Approach Point. Notice the absence of the Maltese Cross. Also notice the notes in red to the right:



No FAF symbol. FAF begins when established inbound.




Another note points to a Missed Approach Timing box with blank spaces where times would be:


MAP based on station passage (VORTAC). Note absence of timing criteria.








If you are looking at the plate for an ILS approach (precision approach), check out the profile view. You will see a lightning bolt in there somewhere. That lightning bolt is showing you minimum decent prior to crossing the outer marker if you have not intercepted the glide slope or minimum glide slope intercept altitude.



The lightning bolt is the Glideslope Intercept Altitude. It may be a minimum, or it may be a mandatory altitude.

ILS or LOC RWY 08 CASPER/NATRONA COUNTY INTL (CPR) (http://204.108.4.16/d-tpp/0612/00072IL8.PDF)

Glide slope intercept altitude, depicted by the number with solid horizontal line below and above the altitude (7,100') - Mandatory altitude.

Crossing altitude at JOHNO LOM is 6,696' -- that's the altitude you should be at when you're on the glideslope passing that point.

Minimum FAF altitude is 6,700' (for the Non-Precision Approach)

In fact, this approach even includes a note, "Glideslope unusable above 7100."


If this approach is flown as a LOC, the minimum altitude prior to the Non-Precision FAF is 6,700', a full 400' lower than the Glideslope Intercept Altitude, 7,100', as your description would indicate.







The point of having a FAF on an ILS doesn't go to much further than a place to start your time for the missed (in case you loose the glide slope) and a convenient place to put the gear down (its more than that, but for simplicity's sake...).




The point of the FAF is to define the beginning of the Final Approach Segment of the Non-Precision Approach.

FAA Instrument Flying Handbook (Chapters 1-7) (http://www.faa.gov/library/manuals/aviation/instrument_flying_handbook/media/faa-h-8083-15-1.pdf)

Figure 7-23. Instrument Landing System on page 7-28 (or Page 151 of 163 in the PDF Document) is a diagram of the components of the ILS. It says this about the Outer Marker:



Provides final appraoch fix for non-precision approach





FAA Instrument Flying Handbook (Chapters 8-11) (http://www.faa.gov/library/manuals/aviation/instrument_flying_handbook/media/faa-h-8083-15-2.pdf)

Figure 8-10. IAP profile legend on page 8-21 (or Page 21 of 118 in the PDF Document) is a legend of symbols used on Instrument Approach Procedures. It says this about the Maltese Cross symbol:



Final Approach Fix (FAF) (for non-precision approaches)









Now, about the glide slope. If you are cleared for the approach, have course guidance with the localizer and you are above the minimum altitude for that portion of the procedure, you can intercept the glide slope and start tracking it down, even if you are 10 miles out at 6000 feet.




Sometimes, yes, sometimes, no.


Refer again to the approach at Casper:
ILS or LOC RWY 08 CASPER/NATRONA COUNTY INTL (CPR) (http://204.108.4.16/d-tpp/0612/00072IL8.PDF)

Since the Glide slope intercept altitude is a Mandatory altitude, 7100', you cannot start tracking the glideslope anywhere you please. Again, look at the note, "Glideslope unusable above 7100."






If none of the things that I mentioned earlier are working or you are unable to identify that particular point, there is one more way to find it.
Looking at the profile view of the plate again, you will find that where the glide slope intersects the FAF, there is a little number there. If you are flying dead-nuts on the glide slope, when you descend through that altitude, you have reached your final approach fix.



Nope.

That little number is the Glideslope Outer Marker Altitude. It does not depict the final approach fix. Again, back to the Casper approach. The Final Approach Segment of the ILS RWY 08 begins when intercepting the glideslope at 7,100. That altitude you refer to, 6696, is not encountered until some 1.4 NM later.





If you are flying an ILS procedure and the Glide slope is INOP, then the procedure just became a non-precision approach, more specifically, a localizer only approach.



Maybe.

Not in this case:

ILS RWY 14 ANCHORAGE / TED STEVENS ANCHORAGE INTL (ANC) (http://204.108.4.16/d-tpp/0612/01500I14.PDF)

Notice there is no Maltese Cross, no Final Approach Fix depicted. There are also no LOC minimums published. If you lose the glideslope after established on the Final Approach Segment, execute the Missed Approach Procedure.




As far as I can tell, this is the scenario that you are presenting: You are setting up for an ILS approach with the glide slope INOP and the outer marker OTS and you are trying to define the FAF.



I did not interpret the scenario quite the same way you did. There were two questions:

1) Does the ILS have an FAF?

This question was addressed in the referenced thread. The Final Approach Segment for an ILS begins at the point where the airplane joins the glideslope, at (or below in some cases) the published glideslope intercept altitude. Prior to this point, the airplane is on the Intermediate Segment. Beyond this point, the airplane is on the Final Approach Segment (and depending on the operation, some rules regarding weather may apply). Since this point is not necessarily assoicated with a geographical FIX, the answer to the above is NO. If you want to press the issue, you might get away with saying, "Not exactly."

The second question is conditonal on the first:

2) If it does, how can you identify it if ...

Well, the answer to the first makes the continued reading of the second moot. If there is no Non-Precision approach published in conjunction with this approach, there's no sense discussing how to find where the Glideslope Intercept Altitude intersects with the glideslope. If there's no glideslope, it's just not there.





You also might be able to find a cross radial from a near-by VOR. It may not be depicted on your plate, you might find it on the low chart, or as part of a different approach, but as long as it is the same fix, the numbers will work.



Feeder routings are useful for situational awareness, but they do not define FIXes.







The point of the post was geared toward the question. The scenario is that there is not a glideslope (lightning bolt and GS intercept are no longer factors) and there was no OM. And we are trying to identify a point in space, namely the point that lets us descend.



If there is no glideslope, the theoretical Precision FAF doesn't exist, so it's futile to look for it. Unless there is a non-presicion approach built into the procedure, it can't be flown.

No sense in chasing windmills, right?





... I time all of my ILS approaches from the FAF (even if it is just for non-precision) just in case I lose my glide slope.



If you've been fortunate to have that option on every ILS you've ever flown, that's great. I'm here to tell you that's not an option on every ILS out there. Icing is no excuse for making bad decisions.




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AVIVIII
12-03-2006, 08:30 PM
You are right, I did make some generalizations. However, I do believe that the exceptions that you are citing are so specific that they completely make it impossible to give a general model. Each approach is going to have some deviations, but how is someone to know whether or not its normal or abnormal unless they have some sort of basis of knowledge.

I did jump to the conclusion that there was not a specific approach in mind, based on the question. But then a general question demands a general answer.

Some of the options that I gave obviously were not ideal, but if you were in that situation that you needed to fly that approach, you would get information wherever you could as well.

One last thing, is that no where did I ever say that that any of this is an excuse for bad decision making. You forgot to quote the part where I said "Choose a different approach." But if your experience is commensurate with your knowledge, I'm sure you have wound up in a spot that you didn't want to be in either.

Again, i apologize for the generalizations, but the goal was to give a basic picture and wait for a further question. Unfortunately, this thread has turned into a carbon copy of the last one that was posted by the same person, and I can't help but feel that he is no closer to understanding his question.

TonyC
12-03-2006, 08:54 PM
Fair enough. It was the end of a long post... perhaps I should have shelved it and reviewed it before I posted. I probably misinterpreted your mention of icing or bad weather to mean you'd be in a situation where you couldn't do the approach over. As long as we both understand that you can only revert to the non-precision approach if there is actually a non-precision approach "under" there, then I'm happy.


As far as this thread taking a turn...

I'm of the opinion that this is a subject that requires precise language to accurately understand. It requires great care when answering specific questions, because the "generic" language we used when we were first introduced to these animals does not always produce the exactly correct answer. It is often the case that the misunderstandings that pop up are a direct result of misapplying those generalizations that we first heard. I'm not perfect -- far from it -- but I try to be as accurate and precise as possible when talking about this kind of stuff in order to AVOID misunderstandings. Correct terminology is critical to effective communication here.



And it really helps when we get away from the vanilla training world and into the raspberry and strawberry and macadamia nut world of "unusual" approach procedures in the real world.


:)



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AVIVIII
12-03-2006, 09:13 PM
Very well put and I do understand where you are comming from.

I'm just glad that this board is differentfrom many of the pilot boards that are out there. I could see this getting to a flame-fest real quick if it was posted out there. So thank you for your knowledge, experience and understanding as well.