Avro85
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LOC And Appr Modes On A318

Sun Dec 04, 2005 12:10 am

Hi all,

I have a question regarding both LOC and APPR mode on the A318.

I was told by a pilot that when doing an ILS approach you first select the LOC mode until the localizer is established and then you select the APPR mode to catch the GS.
is this true ? Because from what I know, in other planes i.e the B727, you directly select the APPR which will first intercept the localizer and then the GS.

I doubt the above statement I was told is true since it would mean that the APPR mode of the new airbus planes is less sophisticated than on the B727....

Anyway, some help would be appreciated.


Cheers
Chris


[Edited 2005-12-03 16:19:10]

[Edited 2005-12-03 16:19:57]
 
wing
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RE: LOC And Appr Modes On A318

Sun Dec 04, 2005 12:23 am

I am not sure about the 318 but on the 320 and 321 you can select the approach button directly when you are cleared for an ILS approach.I dont see why 318 should be any different though.

The only time I use the LOC button when you are cleared only to intercept localiser and the approach clearence is issued later by the ATC.Also it may be a good idea to use the LOC button first if you are outside of the 8/18 NM cone to prevent a false capture with other airport in the vicinity.
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Avro85
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RE: LOC And Appr Modes On A318

Sun Dec 04, 2005 12:35 am

Alright, many thanks for your answer Wing.
 
jush
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RE: LOC And Appr Modes On A318

Sun Dec 04, 2005 1:20 am

You can hit the Appr button immediately but you can use LOC first as well.
How things are handled in different airlines? I don't know. But i guess it's a question of how long your approach is anyways.

Regds
jush
There is one problem with airbus. Though their products are engineering marvels they lack passion, completely.
 
julesmusician
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RE: LOC And Appr Modes On A318

Sun Dec 04, 2005 2:44 am

Ah there are reasons behind this. Often when on approach air traffic will place you at an altitude and ask you to let you know when you have captured the localiser. Obviously if ATC have given you an altitude they want you to be at then if you hit the APPROACH button you will start trying to find the localiser and the glideslope and start ascending/descending to capture it, that is why ATC often ask you to stick to localiser and an altitude first.

Typical approach ATC conversation on the last bits of approach:

"descend 4000ft, QNH 987, turn 210 degrees, contact when localiser established speed 180 knots please"

then

"descend on the ILS, speed now 160 knots until 4 DME"

So it is useful to have both features.
African Civil Aviation Commission president "You don't want to fly out as a passenger and come back as cargo."
 
VuelingAirbus
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RE: LOC And Appr Modes On A318

Sun Dec 04, 2005 3:19 am

Quoting Julesmusician (Reply 4):
if you hit the APPROACH button you will start trying to find the localiser and the glideslope and start ascending/descending to capture it, that is why ATC often ask you to stick to localiser and an altitude first

The autopilot or flight director does not capture the glide slope before capturing the localizer. The plane will not decent and if you capture the LOC and you are above the glideslope it will not capture either. ATC often asks you to only lock on the localizor (and descent and maintain altitude) if you have parallel runway operations to protect the other traffic from overshooting the LOC and as soon as you are established you get the approach clearance. The localizor established call is normally used to hand you over to tower for the landing clearance.
 
Avro85
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RE: LOC And Appr Modes On A318

Sun Dec 04, 2005 3:28 am

Thanks again for your inputs. I know now that we were both correct. The APPR on the 320 family would do the job as well, but due to operations it is sometimes asked to only establish on LOC while holding at specific altitude.



Quoting Wing (Reply 1):
Also it may be a good idea to use the LOC button first if you are outside of the 8/18 NM cone to prevent a false capture with other airport in the vicinity.

But there could be some interferecne with different localizers from different close airport as well then. I mean the GS pattern has a smaller range than the LOC pattern. So if the GS can interfere the LOC can certainly as well.... OK it's less dangerous to be off centered for a while than at a wrong altitude on aproach  Wink

Chris
 
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Jetlagged
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RE: LOC And Appr Modes On A318

Sun Dec 04, 2005 9:59 pm

Quoting Avro85 (Thread starter):
Because from what I know, in other planes i.e the B727, you directly select the APPR which will first intercept the localizer and then the GS.

A 727 with APPR mode? An unheard of luxury for production 727s I think, even the -200adv  Smile
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
NAV20
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RE: LOC And Appr Modes On A318

Sun Dec 04, 2005 11:06 pm

I'd have thought that it's a matter of 'discipline'. You're cleared to intercept the runway line, but you're not cleared to descend until you get landing clearance. So you've got no business programming the aeroplane to descend anyway at that early stage.

In the event of something going wrong ahead of you the controllers will be busy! They're entitled to assume that you'll continue on the vector/altitude assigned to you until further advised. Not go ahead and start down anyway.  Smile
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VuelingAirbus
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RE: LOC And Appr Modes On A318

Mon Dec 05, 2005 1:38 am

Quoting NAV20 (Reply 8):
You're cleared to intercept the runway line, but you're not cleared to descend until you get landing clearance.

The landing clearance has usually nothing to do with the approach. The approach controller or director will issue an approach clearance and that includes the vertical profil as well. According to ICAO standard phraseology you will get instuctions (speed, heading, altitude...), advisories (traffic, wake turbulence...) and clearances (take off, approach and landing). If you are not cleared it will sound like that (ALN = AirLinersNet):

ALN 221, left turn heading 300 to intercept localizer 27L descent and maintain 4000 feet until further advised.

or in case of clearance:

ALN 221 , descent 4000 feet, turn left heading 300 final vector, you are cleared for the ILS 27L, advise established.

And there are busy airports like paris cdg with parallel runways where you MUST intercept the localizer if you are on an intercept course (according frensh authorities), which is not an approach clearance. However an approach clearance ALWAYS includes the vertical profil as well.

hope that helped
 
wing
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RE: LOC And Appr Modes On A318

Mon Dec 05, 2005 6:13 pm

Quoting Avro85 (Reply 6):
But there could be some interferecne with different localizers from different close airport as well then. I mean the GS pattern has a smaller range than the LOC pattern. So if the GS can interfere the LOC can certainly as well.... OK it's less dangerous to be off centered for a while than at a wrong altitude on aproach

A false capture is a little bit different than you have imagined. Wink If you are cleared for the APPROACH at 30 NMs you select the LOC first and press the APP button around 20-18 NMs.
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