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LTU932
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Question On The ILS System

Fri May 19, 2006 10:16 am

This came up in Aviation Hobby, and I decided to ask around here on this. Is the category for which the ILS is certified also a factor on whether it has a DME as well? Some airports have an ILS/DME approach (SJO is one), and some others don't have a DME.

For example, if the ILS is a CATIIIb, would it be required to have a DME? And if a DME equipped ILS is required for a CATIIIb or CATII ILS, which categories require the DME equipment for the ILS overall?
 
Pihero
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RE: Question On The ILS System

Fri May 19, 2006 10:36 am

Quoting LTU932 (Thread starter):
if the ILS is a CATIIIb, would it be required to have a DME? And if a DME equipped ILS is required for a CATIIIb or CATII ILS, which categories require the DME equipment for the ILS overall?

The basic requirement for an ILS is to provide, along with the final path (glide and localizer ) a distance information, at a Final approach fix so that the altitude of the glide slope could be verified.
That distance information can be provided by a marker beacon, a VOR radial on the side or a DME regardless of its position on the runway extended centerline.
Precision approaches approval only depends on the quality of the glide and Loc beams and the redundancy of the equipment, electrical power supply and so on.
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LTU932
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RE: Question On The ILS System

Fri May 19, 2006 11:01 am

Quoting Pihero (Reply 1):
Precision approaches approval only depends on the quality of the glide and Loc beams and the redundancy of the equipment, electrical power supply and so on.

I see now. So in the end, a DME is not required for the ILS itself, though it would be useful for the equipment redundancy you mention.

Quoting Pihero (Reply 1):
That distance information can be provided by a marker beacon

Since you're mentioning the distance information at the final approach fix of the respective runway, which marker are you referring to (Outer, Middle or Inner)? And how far away are those three markers from each other?
 
PhilSquares
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RE: Question On The ILS System

Fri May 19, 2006 11:24 am

Quoting Pihero (Reply 1):
The basic requirement for an ILS is to provide, along with the final path (glide and localizer ) a distance information, at a Final approach fix so that the altitude of the glide slope could be verified.

Just a minor technicality, there is no FAF with an ILS. The "maltese cross" is the FAF for the Localizer only portion. I do agree about the altitude check, although I don't believe it's actually required.
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Pihero
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RE: Question On The ILS System

Fri May 19, 2006 6:50 pm

Quoting Philsquares (Reply 3):
there is no FAF with an ILS

You are righ, Phil. But I can't find any better english word for what we call in France "la porte",litterally "the door" at which you validate the altitude interception of the glide.
Lack of this info makes the DA a lot higher.
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pilotpip
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RE: Question On The ILS System

Sat May 20, 2006 5:15 am

The only time that DME is required in an ILS approach is if the name specifies so. The ILS/DME you ask about requires DME to identify some sort of fix on the approach, perhaps an initial approach fix or something on the missed approach procedure. If you're not DME equipped you cannot utilize this approach. GPS may take the place of DME.

Typically, Outer markers are about 5 to 6 miles from the runway. I don't know exactly about middle markers because none of the approaches I frequent have them and the FAA is in the process of decomissioning them.
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Mir
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RE: Question On The ILS System

Sat May 20, 2006 10:36 am

Quoting Pilotpip (Reply 5):
I don't know exactly about middle markers because none of the approaches I frequent have them and the FAA is in the process of decomissioning them.

IIRC, they're about half a mile from the runway. I find them pretty handy, since when I start hearing them I know I'm pretty much at minimums (assuming standard ILS minimums) and need to see that runway ASAP unless I want to go around.

-Mir
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Ralgha
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RE: Question On The ILS System

Mon May 22, 2006 2:48 am

Quoting Philsquares (Reply 3):
Just a minor technicality, there is no FAF with an ILS.

Yes there is, the FAF on an ILS is on the glideslope at the lowest intercept altitude, however it is not marked with the cross as non-precision approaches are.
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Pihero
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RE: Question On The ILS System

Mon May 22, 2006 2:55 am

Quoting Ralgha (Reply 7):
the FAF on an ILS is on the glideslope at the lowest intercept altitude, however it is not marked with the cross as non-precision approaches are

Ralgha, DON'T YOU START ANOTHER DISCUSSION ON DIFFERENCES BETWEEN NATIONAL REGULATIONS ! Smile
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Ralgha
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RE: Question On The ILS System

Mon May 22, 2006 3:08 am

Philsquares started it by saying there isn't a FAF so point the finger at him!  bigthumbsup 
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zeke
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RE: Question On The ILS System

Mon May 22, 2006 3:49 am

Quoting LTU932 (Thread starter):
For example, if the ILS is a CATIIIb, would it be required to have a DME? And if a DME equipped ILS is required for a CATIIIb or CATII ILS, which categories require the DME equipment for the ILS overall?

A DME is not required, however it becoming more of the norm, its a cost saving to have one DME serving both ends of a runway than having multiple markers. Some countries allow the use of GPS in lieu of DME.

Quoting Philsquares (Reply 3):
Just a minor technicality, there is no FAF with an ILS. The "maltese cross" is the FAF for the Localizer only portion. I do agree about the altitude check, although I don't believe it's actually required.

This is from the ICAO Procedures for Air Navigation Services, Volume II, you can in extreme cases have a FAF on an ILS. You are correct in most cases you do not, you have a FAP. Most FAFs depicted on charts are not for the ILS approach, they are the LLZ,, they are a ILS/LLZ charts with both approaches overlaid.


1.4 PRECISION SEGMENT

1.4.1 General
The precision segment is aligned with the localizer course and contains the final descent for landing as well as the initial and intermediate phases of the missed approach segment See Figure 11-1-1-5.

1.4.2 Origin
The precision segment starts at the final approach point (FAP), that is, the intersection of the nominal glide path and the minimum altitude specified for the preceding segment. The FAP should not normally be located more than 18.5 km (10.0 NM) before threshold, unless adequate glide path guidance beyond the minimum specified in Annex 10 is provided.

1.4.3 Descent fix

1.4.3.1 A descent fix may be located at the FAP to overcome certain obstacles located before the FAP as an alternative to increasing the glide path (GP) angle. When so located, it becomes the final approach fix. The extension of the precision surfaces into the precision segment is then terminated. . The descent fix should not normally be located more than 18.5 km (10.0 NM) before threshold, unless adequate GP guidance beyond the minimum specified in Annex 10 is provided. The maximum fix tolerance is +/- 0.9 km ( +/- 0.5 NM). Where DME is used to identify the fix, the range shall he stated in tenths of kilometres (nautical miles).
Note.- Guidance material for determining the distance to the descent fix froom the threshold is contained in Appendix D.

1.4.3.2 Obstacle clearance at the descent fix

1.4.3.2.1 When a descent fix is provided , the precision approach surfaces start at the earliest point of the FAF tolerance area (see Figure 11-1-1-2). The provisions of Part 1, Section 3, Chapter 2, 2.7.4, "Obstacle close to a final approach fix or stepdown fix" which allow obstacles close to the fix to be ignored, apply in the area below the 15 per cent gradient within the precision surfaces (Cat H, 15 per cent gradient or the nominal gradient multiplied by 2.5,
whichever is greater).

1.4.3.2.2 Where a descent fix is not provided at the FAP, no curtaibnent of the precision surfaces is permitted (see Figure 11-1-1-3).

1.4.3.2.3 if the precision surfaces are extended into the preceding segment, they shall not be extended beyond the intermediate approach segment.
1.4.4 Glide path verification check A fix (outer marker or DME) is necessary so as to permit comparison between the indicated glide path and the aircraft
altimeter information. The fix shall not have a fix tolerance exceeding i 0.9 km (A 0.5 NM). When DME is used to identify the fix, the range shall be stated in tenths of kilometres (nautical miles).
Note.- Guidance material for determining the height crossing the outer marker is contained in Appendix D

1.4.5 Missed approach
The missed approach point is defined by the intersection of the nominal glide path and the decision altitude height (DNH). The DNH is set at or above the OCAIH, which is determined as specified in 1.4.7 to 1.4.9 and 1.5.

1.4.6 Termination
The precision segment normally terminates at the point where the final phase of the missed approach commences (see Part I, Section 4, Chapter 6,6.1.2, "Phases of missed approach segment") or where the missed approach climb surface Z (starting 900 m past threshold) reaches a height of 300 m (984 ft) above threshold, whichever is lower.

Quoting Ralgha (Reply 7):
Yes there is, the FAF on an ILS is on the glideslope at the lowest intercept altitude, however it is not marked with the cross as non-precision approaches are.

I think your referring to the FAF on the LLZ, most ILS approaches do not have a FAF, most only have a FAP. A FAF is normally only included on an ILS where extreme terrain exists.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
Pihero
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RE: Question On The ILS System

Mon May 22, 2006 5:28 am

After a conference like that, we bow and say thank you, Sir.
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PhilSquares
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RE: Question On The ILS System

Mon May 22, 2006 7:56 am

This is from the ICAO Procedures for Air Navigation Services, Volume II, you can in extreme cases have a FAF on an ILS. You are correct in most cases you do not, you have a FAP. Most FAFs depicted on charts are not for the ILS approach, they are the LLZ,, they are a ILS/LLZ charts with both approaches overlaid.

Zeke, thanks for the link. However, just a point of clarification, those fixes are called PFAF. See http://www.faa.gov/about/office_org/..._guidance/tils/media/TIL01023A.pdf
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zeke
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RE: Question On The ILS System

Mon May 22, 2006 10:41 am

Quoting PhilSquares (Reply 12):
Zeke, thanks for the link. However, just a point of clarification, those fixes are called PFAF. See http://www.faa.gov/about/office_org/...A.pdf

That is yet another non standard FAA term, it is not ICAO, thats a TERPS term. Have a look in th introductory section of the Jepps next time you fly, you will see the terms defined, and see how the FAA could not be standard yet again.
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