ILS/DME Approach

[knightflt]

Greetings my fellow aviators. I have been pondering this for a while and have not satisfied myself with a proper answer (reinforced by a paper reference). What is the main difference between the ILS and the ILS/DME approach when you consider that a typical Cat 1 approach, the localizer is intercepted at a specified altitude until GS intercept, then down to a DH where a decision is made to land/Go Around. At no point is a distance required on the approach.

My only thought is that the DME portion would only be pertinent in a missed approach when a DME would be required in the Missed approach phase. My other thought of the pertinence of the DME on the localizer would be for a LOC only portion in case of a failure of the GS while on the approach which reverts to a LOC approach. If the LOC requires distance based on the DME of the LOC rather than a VOR , then I would again see the significance.

The simple question is this, why not just call it an ILS approach rather than the ILS/DME approach?. Also if the DME of the LOC is notamed inoperative, can you fly the ILS/DME approach (localizer and GS operative), and what is your DH? Is it a LOC MDA or the published ILS DH?

[clivewatson]

Good question. The answer in part may be found here:

Instrument Procedures Handbook (IPH) (http://www.faa.gov/library/manuals/aviation/instrument_procedures_handbook/)

(Chapter 5 refers)

The navigation equipment that is required to join and fly
an instrument approach procedure is indicated by the title
of the procedure and notes on the chart. Straight-in IAPs
are identified by the navigation system by providing the
final approach guidance and the runway with which the
approach is aligned (for example, VOR RWY 13).
Circling-only approaches are identified by the navigation
system by providing final approach guidance and a letter
(for example, VOR A). More than one navigation system
separated by a slant indicates that more than one type of
equipment must be used to execute the final approach (for
example, VOR/DME RWY 31). More than one navigation
system separated by the word “or” indicates either
type of equipment can be used to execute the final
approach (for example,VOR or GPS RWY 15).
In some cases, other types of navigation systems, including
radar, are required to execute other portions of the
approach or to navigate to the IAF (for example, an NDB
procedure turn to an ILS, or an NDB in the missed
approach, or radar required to join the procedure or identify
a fix). When ATC radar or other equipment is required
for procedure entry from the en route environment, a note
is charted in the planview of the approach procedure chart
(for example, RADAR REQUIRED or ADF
REQUIRED). When radar or other equipment is required
on portions of the procedure outside the final approach
segment, including the missed approach, a note is charted
in the notes box of the pilot briefing portion of the
approach chart (for example, RADAR REQUIRED or
DME REQUIRED). Notes are not charted when VOR is
required outside the final approach segment. Pilots should
ensure that the aircraft is equipped with the required
NAVAIDs to execute the approach, including the missed
approach.


I assume Europe have a similar document.

[roljoe]

Hi,

well according to me..I always keep the thing simple...This means that if the title of the approach plate is ILS/DME..you need both system to work 100% to be able to shoot this approach..and this in respect of the stated minima..
This lead me to the rest of the question...if any of the system required is not available..specific minima must be stated..w/o dme >>> or G/S out>>etc..

hope this help you a bit...:)

[clivewatson]

exactly as the first three lines of my post states - couldn't be any simpler!

i've edited with bold type face to make it REALLY simple!

[Bullethead]

Another point worth considering, some ILS approaches don't have an outer marker beacon with which to make a glideslope height check and so use a DME/height check instead. If the DME is U/S then the approach, ILS or LLZ, can't be used.

Regards,
BH.

[knightflt]

Thank you all for your informative replies. I felt like I was a contestant on the game show "Who wants to be a millionaire" and I had to use the "ask the audience" lifeline. The point of the G/S intercept height check without an outer marker was well taken. Again..thank you all

Knightflt

[flyburg]

Another point to consider. The inoperative component table. On top of my head it states "any other means to identify" The 73's we fly all have 2 GPS's. That to me satisfies the requirement,in any case that's the general opinion at my company.

Greetings

[poldek77]

Does anyone have any idea about ILS procedures without a fix for altimeter check? Recently I flew to Antalya, Turkey (LTAI) and they serve ILS36C approach w/o DME, markers or locators but DH=200' (for those using Jepp RM it's page 11-6)? - sorry, I'm not able to paste the chart here...
Greetings

[Tinstaafl]

Does the approach use a cross bearing from a VOR or NDB to fix the correct GS intercept location?

[poldek77]

Does the approach use a cross bearing from a VOR or NDB to fix the correct GS intercept location?


No, it doesn't. You start over Locator Middle Marker at 3000' (the only locator and marker in the procedure) - that's 0.6NM from the threshold, follow LOC outbound for 2 minutes descending to 1500', then 45/180 procedure turn, to intercept and follow the ILS. In fact there is one published fix with altitude - over MM 410'(234'), and DA/H 376'/200'. But MDA/H for LOC(GS out) is 510'(334').

[411A]

descending to 1500'....

With this type of ILS procedure, a crossing height check is not required, nor desired, because....if you follow the procedure as outlined, no glidepath problems will be encountered.

Quite common in many parts of the world.

[downwindabeam]

Usually a procedure is developed as an ILS/DME if no other means are available to reference important parts, points and segments of that approach.

For instance, let's say there is no VOR with which you can verify your location over the outer marker. Or let's say there is no way of verifying your missed approach point when the GS becomes suddenly inoperative and you revert to a LOC non precision approach? (Remember you can climb but are requested to not turn anywhere until you get to that golden MAP).

Also in modern installations the DME has become a cost effective solutions to replacing the marker beacons in their entirity. You can verify the equipment from one centralized location and don't have to worry about 2 sometimes 3 more installations (ref: OM, MM, IM).

As for your original second and subsequent questions. If a procedure is named an ILS/DME approach, you can consdier that a contract between you and the local aviation authorities. Therefore if the DME portion is notamed out of service, the procedure cannot be used.

Usually most of these procedures will note RADAR or DME required, and then as long as you are within positive RADAR control, you are allowed to use that approach even if the DME is notamed.

As a final note. Please search on youtube for an Air Newzeland 757 (maybe it was a 767) that had made an approach to an unmonitored ILS and have gotten errornous glide slope indications. Referencing a DME or any other kind of locator, intersection verification vs. altitude provided their life saving ticket.

Air NZ and errornous ILS indications.

Good luck!

[poldek77]

descending to 1500'....
With this type of ILS procedure, a crossing height check is not required, nor desired, because....if you follow the procedure as outlined, no glidepath problems will be encountered.


Why is the altimeters check not required/desired here? Maybe the glidepath is working properly but what about my altimeters?


(...) an Air Newzeland 757 (maybe it was a 767) that had made an approach to an unmonitored ILS and have gotten errornous glide slope indications...

the original title is "A free lesson. Flight NZ60".

[snips]

ICAO Annex 10 Vol 1 has the specs for ILS systems. Should be a link to the docs at the top of the flight deck forum.

The complete ILS system has markers in it, though these can be replaced by DME system. If the markers or DME are not available then the system is not complete/cannot be used.

However the may be a chance to use it as a NPA ie LOC only with different minima but that down procedure design and CAA

[Tinstaafl]

Oh. You didn't say it was a procedural reversal type of ILS. Like 411 says, the procedure ensures you capture the correct GS.

Poldek, the check using the altimeter at the OM isn't to check the altimeter. You're using the altimeter's altitude at the OM to check & confirm that you have intercepted the correct GS and not a side lobe.

[411A]

If the markers or DME are not available then the system is not complete/cannot be used.



The ILS has been in use since 1938, was developed by Reed Pigman and Sperry jointy at that time, and has many installations where there is no marker, LOM, DME fix, VOR crossing radial etc, and is easy to use.
Pilots should not try to re-invent the wheel nor throw up obstacles to its use, without good reason.

If, on the other hand, you (or your company) using a procedural course reversal ILS procedure without any of the afore mentioned fixes, the choice is quite simple....divert, and land somewhere else, if necessary.:rolleyes:

NB.
Capt Pigman, being quite a clever guy, also had a hand in developing the VOR system of navigation

[poldek77]

the check using the altimeter at the OM isn't to check the altimeter. You're using the altimeter's altitude at the OM to check & confirm that you have intercepted the correct GS and not a side lobe.

I think it's even easier to detect a false GS lobe looking at your VSI at any moment after GS capture, not only at OM.

[Tinstaafl]

Rate of descent is proportional to Groundspeed. Into a strong headwind you will have a much reduced ROD. Without a DME to give groundspeed wrong GS capture is not so obvious using the VSI.

[punkalouver]

Another point worth considering, some ILS approaches don't have an outer marker beacon with which to make a glideslope height check and so use a DME/height check instead. If the DME is U/S then the approach, ILS or LLZ, can't be used.




Not necessarily true. Here in Canada and the U.S. if the DME is u/s an aircraft can use an appropriately approved GPS unit using a DME waypoint retrieved from a current database as a substitute for an unserviceable(or serviceable DME) waypoint based on DME.

[senshi]

Punkalouver... beat me to it!

Are you able to advise of what is classified as "an appropriately approved gps unit"? Does that mean TSO129c at the minimum?

S

[411A]

Does that mean TSO129c at the minimum?



Yup, and installed and approved for IFR terminal/approach procedures.

[JAR]

1ILS:
Acft unable to receive DME
advise ATC. Radar ranges will
be provided at 7 NM outbound
and 4 NM inbound.

[411A]

All very interesting, IGh, however, one is not going to be assured about inaccurate glidepath signals without fault monitoring in the aircraft and on the ground.
DME readouts on approach, while assisting to some extent, are not, IMO, the ultimate solution.
Likewise for the localizer signal.

A better solution was the MLS, but that seems to have slipped into oblivion.

[BOAC]

Bring back the marker beacon (and the NDB - as long as I don't have to fly an approach on it...................................)

[Graybeard]

Igh: "Alitalia DC-9 / 14Nov90 DC-9-32 I-ATJA , ILS- CFIT; … flew about 900' too low on approach to Zurich … into a hill about 9.6 km from the city's airport at night. Fatal=40 passengers + six crew. … false Glide Slope indication with no Flag … "

That accident was a combination of Alitalia's complex ILS cockpit configuration, which left just one ILS receiver usable on that approach, and a KNR-6030 VOR/ILS receiver that had a history of intermittent false indications with no monitor channel to catch errors.

A DC-8 cargo captured a false localizer beam at Cold Harbor in Alaska in the mid-1970s, and hit a mountain in the dark.

GB

[eckhard]

One important lesson I picked up from the ANZ incident is that it is important to check DME against altitude (not the other way round).

In other words you should say,

"We're now passing 1800ft, what should the DME be reading?"; instead of,

"We're now at 6DME, what should the altimeter be reading?"

The reason is that if you are inadvertently low, it may be dangerous to wait until a certain DME check point before verifying the altimeter reading.

For example: "We're now at 6DME, the altimeter should indicate 1800ft. Hey! It indicates only 1500ft! Why is that?.. -- >::Sound of impact::<

Far better to say, "We're now at 1800ft, the DME should indicate 6DME. Hey! It indicates 7DME! We must be too low! ::Sound of engine power increasing::

What does your company teach?

[Tinstaafl]

'DME' to Altitude or 'Altitude to DME' I think is much of a muchness, although I'm willing to be convinced otherwise. In the scenario given above for the favoured technique the final event could equally have been <crunch!> instead 'Sounds of engine power increasing' (or even a 'Sounds of engine power increasing...<crunch!>'.

[Graybeard]

Further to my post above, IIRC, they had tuned the number 2 VOR/ILS receiver to VOR on field, to get DME distance, and had followed a dead GS needle. GPWS gave no warning, of course, since it was receiving the same 0 GS deviation.

GB

[BOAC]

Always worked on GS intercept point. If below published 'platform', you work out a new one. DME ranges v Heights are not always published on charts.

[BOAC]

IGh - yes. Subject to any range/altitude minima and descent rates, once ESTABLISHED on the localiser, it would be ok. Of course, assuming eventual G/S capture:). Good job too, or I might have 'missed' a few times in AMS:}