Urgent IREX Question! ILS-Y or ILS-Z in the DAPs

[MerlinV8]

Could some please explain to me the main difference in the DAPs between an ILS-Y and an ILS-Z?

For example I have been looking at the approach plates for YSSY and the ILS-Y or LOC-Y RWY 07 and comparing it to the ILS-Z or LOC-Z RWY 07 and the only differance I can find is the DME Distances? which raises another question, how can the distance's be different over head the markers when both they and the DME are fixed aids?

Also why are you given two different options? what is it you are considering when making a choice which one to use?

I am currently self studying the IREX and have practice cyber exams, some of the questions are obviously out of date because they will ask a question on an ILS approach, neither mentioning Y or Z only to find that I am now presented with two choices, firstly do CASA and ASL keep their exams up to date that this won't happen in the actual exam, and if it did which one would I choose?

I have kept my DAPs up to date and also noticed that Z does not always come after Y so does the sequence of the lettering mean anything at all?

Exam not too far away so any help at all no matter how small would be appreciated!!

Thanks!

[Di_Vosh]

There may be a couple of reasons for the Y/Z approaches.

If you look at the reference beacon for the ILS's you've given in your example, the ILS-Y uses the SY DME, and the ILS-Z uses the ILS DME. SO, you'd be foolish to use the ILS-Y if the SY DME was notamed U/S.

If you look at the CBR 35 ILS Y and Z the reference DME is the same. BUT the CBR 35 ILS-Y allows you to have a DA of 2070', much lower than the CBR 35 ILS-Z, which only allows you down to 2100'. The one you use in this case will be dependent on what missed approach climb gradient you aircraft is capable of.

There may be other reasons, but they're the two that I've had experience.

Cheers,

DIVOSH!

[MerlinV8]

Fantastic! Thanks Di Vosh!!

Of course it's obivious after its been pointed out! you know whats like when you've had your head in the books a little too long, things start to blur..... time for a coffee break I think!

Cheers

[MerlinV8]

Ok guys I have another question if anyone can help?

What does IMS stand for regards the DME on the approach plates, its was on a IREX question I came across and can't find the definition anywhere.

YMML ILS-Z RWY 16 in DAPs, look at the approach profile and above NM from RWY it says NM BY IMS DME, what does this mean?

Does anyone know where there might be a more comprehensive legend to the DAPs than just what in the front?

Cheers

[Capt Chambo]

IMS is the ILS's ident.
The legend below is a little confusing as I think it should read "nm from IMS DME" and not "nm by IMS DME".
Hope that helps.

[MerlinV8]

Thanks CC,

I have done some searching on the net but the actual definition is hard to find, can you confirm that it stands for "Interference Monitoring System"?

Also I got asked at what is the distance at which I must reduce to the FAF maximum IAS regards YMML ILS 16 and the choice's included 5.5 and 5.7, as far as speed restrictions go which distance would be the correct one to use? IMS or RWY

[atr725]

The "Y" and "Z" are just identifiers for multiple approaches based on the same navigation equipment to the same runway with diffrent procedures.

[hollingworthp]

They use multiple letters in Italy all the time - the only difference appears in most case to be the missed approach - so I guess it depends which 'dignitary' is at home and doesn't wish to be disturbed by a go around ;-)