Final Approach Fix (FAF)

[Black_Dawn]

Can someone tell me why some non-precision approach procedures (VOR/VORDME NDB) show the Maltese cross as FAF in the profile view and some other non-precision apps don't do that? :confused:

As an example look at the LIML/LIN VORDME18L (with FAF) and LIML/LIN VORDME36R (no FAF:no Maltese cross)

What's the criteria to show or not to show the FAF on a non-precision approach profile view?

thanks
B_D

[frogone]

The charts I'm looking at are both dated 24/02/2006.

36R, you are correct there's no FAF, fair point, I'm not too sure why. However in the footnote 'Changes' it says "Fix withdrawn".

The deal with 18L, is the FAF I believe has been added.

I can't answer the initial question, maybe misprint? However the VOR shoud suffice for the FAF even though it is not marked on the chart with standard cross.

IR

[PRNAV1]

Minimum obstacle clearance (MOC)
for the final segment

Fixed margin for all aircraft
90 m (235') without FAF
75 m (246')with FAF

(FAF -final approach fix)

Relationship of obstacle clearance altitude/height (OCA/H) to minimum descent altitude/height

(MDA/H) for non-precision approaches (example with a controlling obstacle in the final approach)

In the absence of a FAF. descent to MDA/H is made once the aircraft is established inbound on the final approach track. Procedure altitudes/heights will not be developed for non-precision approach procedures without a FAF.
In procedures of this type, the final approach track cannot normally be aligned on the runway centre line.

Whether OCA/H for straight-in approach limits are published or not depends on the angular difference between the track and the runway and position of the track with respect to the runway threshold.

Hope this helps :ok:

[OzExpat]

Yes, PRNAV1 has given you the answer - although 90 metres equates to 295 feet and, under Pans Ops the actual value is 294 feet which is rounded to 90 metres for the equivalent SI value. Thus, for reasons best known to the procedure designer, obstacle clearance in the final segment is 294 (or 295) feet.

Just as a matter of professional interest, can you tell me how far away from the THR was the FAF in the previous procedure? That might help me to explain why it was withdrawn.

[Black_Dawn]

OzExpat

i can't remember the distance :O

If you can look at some Frankfurt non-precision app you'll see they put the FAF (cross) at 12nm. (rulebook states to put the FAF around 5nm!).Maybe the distance is not a factor :confused:

Another good example is LIEE/CAG VOR,VORDME 14, no FAF, but Lctr DME 14
has the FAF (cross).

My question is: why, along the same rwy, do we have a Locator DME proc. with a final fix and a VORDME app without it (no cross)?

B_D

[High Wing Drifter]

Something similar cropped up in my IR sim session today. There are non-precision approachs which permit both DME and non-DME approaches. For such approaches, in the case where the FAF is defined as a distance and not a time from the DME and the DME is not available (for whatever reason) then, once base is complete and within +/- 5deg of the inbound QDM you may begin the descent.

[OzExpat]

(rulebook states to put the FAF around 5nm!)
Not quite. The FAF can be further away but, if it's beyond 5 NM from the THR, the MOC must be at least 294 feet (90 metres). The 5 NM rule allows reduction of MOC to 246 feet (75 metres). Therefore, distance is most definitely a factor.

My internet connection isn't fast enough or cheap enough to allow me to surf the web for any approach procedures but if you look at them in relation to distance from the THR, this might provide a clue. There is just one other possibility, however, which has just occurred to me as a result of your statement :-
Another good example is LIEE/CAG VOR,VORDME 14, no FAF, but Lctr DME 14 has the FAF (cross).
The protection area for a VOR-based procedure is smaller than for a NDB-based procedure. The larger protection area for the latter might include some high obstacles that are not encompassed by the protection area for the former. So, it might be that the FAF is needed to ensure that aircraft are well clear of those obstacles before allowing descent in the final segment.

Or maybe it's for ATC traffic management, or lateral separation, purposes. They need to provide broader separation for aircraft tracking by reference to a NDB because it's less accurate than a VOR.

As you can see, it's a bit difficult to provide any substantive comment without an evaluation of the actual procedures. However, as long as you abide by the specifications on the approach chart, it won't actually matter whether there's a FAF or not.

[Black_Dawn]

OzExpat and the others

thanks for your help

i've scanned the procedure plates for LIEE, but i don't know how to upload them: the insert immage command ask me for a url, but the images are on my computer's harddisk.

any help?
B_D

[dolly737]

Hi B_D,
you need to upload the pic onto an "Image host" server. You'll get an url there which you can link.
There are lots of free sites available, google might help. You may have to downsize the image though (most servers have a max size limit).

[OzExpat]

Black_Dawn... If you're going to upload them to a site, as suggested by dolly737, please downsize them as I can't download large images. This action will also speed your upload.

[Black_Dawn]

Hi all
here are the approach plates (hope i ain't infringing any copyrights!)

This one with FAF
http://i46.photobucket.com/albums/f113/Almd82/Cag_LCTR_DME14.jpg

These ones same runway but no FAF:confused:

http://i46.photobucket.com/albums/f113/Almd82/Cag_VOR14.jpg
http://i46.photobucket.com/albums/f113/Almd82/Cag_VORDME14.jpg
thanks for your help
B_D

[OzExpat]

There's no reason that I can put my finger on as to why the LCTR/DME needs a FAF or why the VOR/DME procedure does not need it. The VOR procedure can't use one because there's no way to identify the fix.

The place is obviously difficult, with lots of obstacles in the vicinity, a Restricted area close by and some other sort of area that cannot be overflown below 1500 feet AGL. That's a useless note, by the way, because there's no indication of the elevation of ground level in that area.

I note that in both the LCTR/DME and VOR/DME procedures, the commencement of final segment of the procedure is markedly different (6.5 and 12.0 respectively). This is probably due to the larger protection area for the base turn in the NDB-based procedure, in relation to it's proximity to the Restricted Area. The protection area for the VOR-based base-turn would be somewhat smaller but I wouldn't have thought that it would make such a great difference (ie 5.5 NM), when the distance between the VOR and NDB doesn't seem to be more than about 3 NM.

Significantly, the 3-degree profile (shown on the VOR/DME chart) starts at 6.4 DME. This seems to be 6.3 NM from the THR, so the MOC on final must be at least 294 feet. The 6.5 DME position identified on the LCTR/DME chart seems to be 6.1 NM from the RWY so, once again, MOC must be at least 294 feet.

In each case, the position at which final approach is commenced can be identified by the pilot without reference to DME (ie by being within the standard tracking tolerance for the final approach track). Thus, I wouldn't have thought that there was any need for a FAF on the LCTR/DME chart. So the best answer I can give you is... "beats the heck out of me!". Had I been designing these procedures, I feel sure that I wouldn't have included a FAF on the LCTR/DME chart.

[Black_Dawn]

OzExpat

thanks for your help:ok:

do you have any suggested reading or book, maybe a site, where i could get something about instrument procedures design?

again thanks
B_D

[discountinvestigator]

ICAO Doc 8168 V2 is the main reference book
For severe techie questions, try the owner of the www.asap.sk (http://www.asap.sk) site if it is still in that area. He is a Kiwi and knows a lot.

However, there are several nasty errors on those plates. I will try to take a look at them later today. My record is finding 18 errors on a plate. Still, actually none of them were related to the reason that the aircraft hit the mountain!

[OzExpat]

Black_Dawn... As stated by discountinvestigator, ICAO document 8168-OPS/611, Volume 2, is the only reference. It's pretty heavy reading and, without some training, will be very difficult for you to understand as it's a very highly technical document.

However, if you want to have a crack at it, think I read, in another thread somewhere on PPRuNe, that the Danes have a lot of ICAO publications online. I don't know if Pans Ops will be one of them, or whether it's completely up to date, but worth checking. Perhaps someone else can identify the thread, or the URL for the Danish website.

[dusk2dawn]

The "Danish URL" is here (http://www.pprune.org/forums/showthread.php?t=214601).

[discountinvestigator]

The Swedes have a good guide as well. However, from someone qualified to oversee designers of these procedures, do not design your own!

[Black_Dawn]

thanks everybody! :)

you were very useful :ok:

B_D

[212man]

The answer may be simply that it is not depicted in the national AIP. At the end of the day, Jeppessen and Aerad do not design the approaches: they copy the National Procedures and present them in their own style.

Having operated in some of the less well regulated areas inthe world, I have seen some abysmal plates from respected companies, but they are hamstrung if the information is eroneous or incomplete: they can't add bits or fill in the gaps themselves.

[discountinvestigator]

I disagree with the previous post by 212 man. I have worked in several areas of the world where the jepps and aerads have had the navigation aids at the correct end of the runway whereas the national AIP has been incorrect.

In addition the commercial companies have published procedures for navigation aids not shown in the AIP.

I routinely work in countries where the AIP is between 2 and 15 years out of date. Of course, your company audit of the airport prior to starting flight operations will detect these issues and then appear on the Captain's brief. And for diversion airports as well. At least in theory....

[212man]

I stand corrected! While not surprised to hear about Navaids being placed correctly (I've reported two errors to Jepp myself) I'm surprised to hear they publish inhouse procedures. There must be some interesting litigation issues there in the event of an accident during an approach.

[OzExpat]

I don't know about Aerad but do know a bit about Jeppesen, having been involved with them for many years. First point is that, when they reproduce a States' charts in their own format, they depend on the data from the State being correct. If it is wrong, their chart will be wrong, simple as that, Of course, they are usually very quick to correct errors when notified.

Jepps have quite a large commercial procedure design office in Atlanta. They do contract work for anyone who wants it - using TERPs or Pans Ops, as dictated by the customer. They also prepare complete AIP to order. I feel sure that they carry a LOT of insurance for this work and am equally sure that it's included in the prices they charge for these services.

I guess that Aerad probably does much the same thing.

[discountinvestigator]

They do carry a lot of insurance. The have designed charts for operators who visit Africa which have been significantly more up to date than the AIP. As stated earlier, they do publish more accurate stuff where possible! I have even been known to send them the odd photo of a VOR which has grown up overnight and nobody seemed to know was there, etc.

[alfalpha]

On a slightly related question can anyone please explain to me the difference between a FAF & FAP?

Thanks in anticipation.

alf

[212man]

Ozexpat and discouninvestigator,
thanks: I didn't doubt their ability or fact that they can design procedures; I was implying it would be unlikely that they would add 'missing' bits to an existing AIP procedure, such as the FAF off their own back.

[OzExpat]

alfalpha, a FAF is associated with non-precision approaches. It is a positive fix.

A FAP, OTOH, is associated with precision approaches because it marks the position for commencement of the precision segment (ie glidepath). It is not, strictly speaking, a positive fix because the actual point of intercept will only be exactly the same as the nominal point if standard ISA conditions exist at the time of GP intercept. To a lesser extent, the point of interception can differ due to altimeter error or a higher altitude at the point of intercept (ie intercepting the GP further out than the nominal distance that's shown in the chart).

212man... there can be many other reasons. Firstly, it might've been an error in the chart produced by the State, which Jeppesen simply copied to ensure that their depiction is identical to the State's own depiction. Secondly, it could simply be an error in the Jepp production.

The only sure way to find out for sure is to ask Jeppesen about it.