airbazar
Topic Author
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Boston (BOS) Centerfield Taxiway

Wed Apr 25, 2012 7:02 pm

After much debate, Boston Logan's centerfield taxiway was finally built. But I've always wondered why it wasn't built exactly between the two runways (4/22 L&R). Does anyone know the reason why the centerfield taxiway was built much closer to runway 4L/22R?

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Photo © Urs Hess

 
vikkyvik
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RE: Boston (BOS) Centerfield Taxiway

Wed Apr 25, 2012 7:38 pm

If you look on Google Maps/Earth at the approach ends of 4R and 22L, you'll see that there are ILS hold points just off of the centerfield taxiway heading toward the runway:

http://maps.google.com/?ll=42.353073...009&spn=0.003088,0.005144&t=h&z=18
http://maps.google.com/?ll=42.376217...098&spn=0.003087,0.005144&t=h&z=18

That'd be my primary guess. You don't want that taxiway to be within the ILS clear zone (or whatever it's called), or you won't really be able to use it during instrument landings.

4L-22R has no ILS, so you can locate the taxiway closer to that runway.
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mmedford
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RE: Boston (BOS) Centerfield Taxiway

Thu Apr 26, 2012 1:07 am

Quoting vikkyvik (Reply 1):
ILS clear zone

ILS Critical Area...


*fill*

*fill*
ILS = It'll Land Somewhere
 
rfields5421
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RE: Boston (BOS) Centerfield Taxiway

Thu Apr 26, 2012 2:40 am

You can clearly see in the picture above the ILS Critical Area markings - and the center taxiway is built as close to those as possible.
 
vikkyvik
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RE: Boston (BOS) Centerfield Taxiway

Thu Apr 26, 2012 6:59 am

Quoting mmedford (Reply 2):
ILS Critical Area...

Thank you! Never remember stuff like that....
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
airbazar
Topic Author
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RE: Boston (BOS) Centerfield Taxiway

Thu Apr 26, 2012 1:42 pm

Quoting vikkyvik (Reply 1):
4L-22R has no ILS, so you can locate the taxiway closer to that runway.

Thanks. I did not know that 4L/22R do not have ILS.
It's interesting however, that at the beninning of the 4's the centerfield taxiway is closer to 4R (and the ILS equipment), then is swerves left and away from 4R.

[Edited 2012-04-26 06:45:04]
 
unattendedbag
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RE: Boston (BOS) Centerfield Taxiway

Thu Apr 26, 2012 1:48 pm

Quoting airbazar (Reply 5):
I did not know that 4L/22R do not have ILS.
http://www.airnav.com/airport/KBOS
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mmedford
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RE: Boston (BOS) Centerfield Taxiway

Thu Apr 26, 2012 5:13 pm

ILS Critical areas, iirc (not in work atm to look at the citing order), it's 35 Degrees from center of the mast (glideslope) or distribution box (localizer), and 1000 feet out. For our CATII/III sites, must be clear during CATII/III operations.

#1 reason, being reflections...also on a localizer, that's CAT II/III. We have what's known as a Far Field Monitor, which monitors the radiated signal. Unexplainable loss in signal can cause a downgrade in category. But i think the caveat with that, is if we enter CATIII & say we lose a transmitter (Our equipment is dual transmitter, with hot standby). We can still maintain CAT-III ILS, but if weather improves, we leave CAT-III and then weather degrades again...we are not allowed to re-enter CAT-III. Assuming no qualified technician is avaliable to look at the equipment.

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ILS = It'll Land Somewhere

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