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Which approach to choose?

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Member
Registered: Jul 2014
Posts: 170
Location: Antwerp
Hi,
Looking at some approach charts for example Frankfurt I am a bit overwhelmed by the different options given for the same runway!
Not being a pilot and no training I have some questions regarding these charts.

The first thing I wonder is, lets assume RWY 25 L is the landing RWY, has the pilot the option to choose which approach to take, or is it ATC that is in charge?

For example,

We have ILS OR LOC 25 L, that is a straight ILS approach with localize and glideslope.

Then there is GLS Z 25 L approach, if I understand correct this is a GPS satelite based Cat 1 approach to DA

The next is RNAV GPS Y 25 L approach, to MDA
Then there is RNAV GPS Z 25L approach, to MDA, this one has VNAV guidance, or what I assume is LPV.( localizer performance vertical guidance)
The FAF for the Y approach is TITUT at 2000 feet
The FAF for the Z approach is LEDKI at 4000 feet.
Why the difference?

So, if given the choice, what is the one to pick?
And is tuning in the ILS , as a backup when the choice is a RNAV good policy?
Any help in the matter would be kindly appreciated
Ivo
Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
I'm not a FFM expert but this is about the only airport in the world that has separate landing thresholds so that aircraft can "land after" .

TITUT is only 5 miles out - hence 2000ft - LEDKI is 11 miles, hence 4000ft...

I would suggest ILS, then RNAV, although in the airport notes they seem to suggest that RNAV is favourite before ILS - I don't know. It would be an ATC thing..

GLS is not allowed on 747. It doesn't have a channel for the necessary GPS updating.

For each particular approach type, the most used is normally the Z, followed by Y etc..
RNAV will automatically tune the appropriate ILS for you if there is one.. :-)

I am sure Hardy and others will have the insight..is it because of wake vortex?

Peter
« Last edit by Britjet on Tue, 21 Jul 2015 19:44:14 +0000. »
Member
Registered: Sep 2014
Posts: 165
Location: Near Paris
I am not familiar with Frankfurt either, but at CDG, it is definitely an ATC thing, because using a procedure or another can have lots of implications regarding other traffic and the separation required.

Basically at CDG we use ILS all the time. LLZ-DME or VOR-DME are used in case of technical problem/maintenance (and we had lots of them in the past year !), or on pilot's request for training, but VERY rare.
RNAV approaches are just used by AirFrance if I remember correctly, but they are just "test" procedure and require ILS monitoring (unless it has changed recently).

At LeBourget (for which we provide approach control at CDG), the use of LPV procedures is on pilot's request only (but need ATC aproval).

So no short answer, except it is highly deendent on the airport, ATC, etc. To know for sure you should get the info from a Frankfurt ATC !

Charles
Member
Registered: Jul 2014
Posts: 170
Location: Antwerp
Thanks for Your help.
i chose Frankfurt as an example, but it can be any other airport!

i did not thought about the fact one is not alone up there and the approach has to fit into the master ATC plan.Certainly at big bussy airports

May I say in general then that the ILS procedure is the prefered one when available ?
And how about visual approaches? In nice clear weather, given the option and the ok from atc, and an ILS approach is also available?

Ivo
Member
Registered: Aug 2014
Posts: 60
Hi,

If an approach uses the same navigational aid approach to an existing approach, but has a difference in the minima, approach angle, missed approach proc, etc it gets a letter appended. The 'default' approach is Z and each subsequent approach goes back a letter.

For example at Heathrow we have Z and Y RNAV approaches. The Z is a bog standard RNAV approach, the Y is identical apart from it is 3.5 degrees rather than 3.

I believe at EDDF the runways are not far enough apart for independent parallel approaches for wake turbulence (they need to be more than 760mtrs apart), therefore the deeper landing approach means the following aircraft is above the wake of the the one the R and therefore wake turn spacing isn't required.
Member
Registered: Sep 2014
Posts: 165
Location: Near Paris
And regarding visual approaches, they are basically forbidden at CDG for "environmental" reasons (meaning noise...).
There were visual approaches at CDG for 20 years but I am too young to have known them.
They are only allowed for emergencies, medevac, etc.
The only visual approach that we use "frequently" is a visual sidetep inside a pair of runways (eg from 26L to 26R). These approaches are allowed on a day to day basis, on pilot's request or ATC proposal (on tower frequency only).
As you see, once again rules are very dependent on where you go. Might be for technical, environmental, or different rules that apply. Even inside a country you can have very specific rules that apply to an airfield only.

Charles
Member
Registered: Jul 2014
Posts: 170
Location: Antwerp
Hi,
First of all thanks again to you all for the explanation, as always I learn a lot of it!

i must say that this forum (meaning his members) ar one of a kind , no matter how many questions one ask, there is always an answer, and most important, always in a kind and polite manner!
Even the dumb or ignorent questions I ask somethimes :-)

---dumb question removed---

And Peter told that on a RNAV approach the ILS is autotuned if available.
So if cleared by ATC for a RNAV approach, at any given time ,when the glideslope and localizer are active , is it allowed to push the APPR button and continue as an ILS approach?

And one more question for You Peter, in your training videos you say "always disconnect autothrottle first"
I have seen many clips and videos where the opposite is done, first the autopilot.
Why the autothrottle first?
Ivo
« Last edit by Ivo de Colfmaker on Wed, 22 Jul 2015 17:36:12 +0000. »
Member
Registered: Sep 2014
Posts: 165
Location: Near Paris
I would definitely say don't push the APPR button !

The aircraft auto tunes the ILS if available but does not know if the signal is correct.
If you have not been cleared by ATC for an ILS approach then you are not sure the ILS is working properly.
Example: you hear ILS 27R in use in the ATIS (which you will probably get 15-30 minutes before arrival). Then between the moment you get the ATIS and the moment you are in contact with approach control, ILS 27R fails. ATC might clear you for another procedure (RNAV or VOR DME for example) because of that failure ! In that case I agree that ATC might warn you that ILS is broken but you never know.
Here is a more vicious example: in the ATIS you hear LLZ DME 27R IN USE. When you are on final you receive full ILS signal. Something that can happen is that ATC clears you for a LLZ DME only because glide is on maintenance. But it will still transmit ! Except that transmitted data MIGHT be totally wrong.

I hope that clarifies things a bit.

And for your last question, Peter comes from a country where they drive on the other side of the road from the rest of us...maybe they do the same when they disconnect automations... :roll:
Okay, I leave...
Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
He he....

We drive on the right side of the road ;-)

About the autopilot/Autothrottle sequence.....
Option 1: take out the autopilot first, leave the Autothrottle in....
You are now hand-flying the aircraft, and any pitch change you make (or maybe a wind change) will cause an aircraft moment due to the thrust couple from the Autothrottle which actually destabilises the aircraft. Eg Suppose you raise the nose slightly - maybe in error....the speed will try to decay and the Autothrottle will increase thrust, causing a nose-up pitching moment, which you now have to fight to correct. As you push forward the Autothrottle will reduce, and you will now have to pull back. etc etc.

Option 2: Take out Autothrottle first. Hands on, get the feel of the thrust lever position. When ready take out the autopilot, and you are now completely manual of course with no annoying pitch couple effects.

Other possibility ( and quite easily done) - take out autopilot and leave Autothrottle in, then forget that you have it engaged, and man land with Autothrottle engaged. Potentially quite dangerous on a manual landing.,.


Peter
"I'm a VERY good driver" ;-)
(actually the Brits drive on the left so that their naturally right-handed horse riders could whip out their swords quickly if they met anyone on the road that they didn't like. Big countries like USA drive on the right ( and so sit on the left) so that they can use whips on the chuck-wagon horses and still judge the clearance to the chuck-wagon coming the other way. (although I personally drive on the left sometimes in the U.S. - it helps in the rush-hour)
I think the French drive on the right because they can...
« Last edit by Britjet on Wed, 22 Jul 2015 18:55:49 +0000. »
Member
Registered: Jul 2014
Posts: 170
Location: Antwerp
Hi Peter,
Thanks for explaining.
It looks like you drive on the (right) side of the road after all!
Ivo

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