Mr Spaceman
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A Taxiway With "3" Hold Short Lines...Why?

Thu Mar 20, 2003 1:54 am

Hi guys.

I noticed somthing interesting to me in the photo below.

The taxiway seems to have "3" Hold Short lines. What would be the reason for this?

Also, is this something that is only done at airports in Britain, or can you find taxiways like this in other parts of the world to? I've never noticed more than 1 Hold Short line at airports in the USA and Canada, but then again, I've probably never noticed anything in detail when looking out the window of an airliner that's taxing into postion because I'm always to darn excited!

I know there's different types of Hold Short lines (some are solid, some are solid with dash lines on one side or the other, some have multiple dash lines), for the purpose of identifying whether or not the runway past the hold Short line is ILS equiped, etc, or not and what category it is.

So, I'm going to venture a guess as to why this particular taxiway has 3 Hold Short lines. Could it be that pilots have to stop short of the line which indicates what landing system is currently in use?


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Photo © Thorbjørn Brunander Sund - Birdlike Multimedia



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777236ER
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RE: A Taxiway With "3" Hold Short Lines...Why?

Thu Mar 20, 2003 1:59 am

The far one is the CAT II/III holding point, the one in the foreground is the holding point for aircraft entering the runway in non CAT II/III conditions. The centre one is a holding point for aircraft EXITING the runway (look at the arangement of it).
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Mr Spaceman
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RE: A Taxiway With "3" Hold Short Lines...Why?

Thu Mar 20, 2003 2:28 am

Hello 777236ER.

Thanks for your reply.

OK, so my suspisions about the purpose of 3 lines was on the right track.

I guess the different positions of these lines is based on safety. If the runway is being operated under CAT II/III conditions, then there's likely a very low ceiling (200 AGL or lower), or fog, etc, and the farther back from the active you are, the better .... incase an arriving aircraft is off the centerline!

I see what you mean by the arrangement of the middle line. So once exiting the runway, if you're going to stop for ATC, etc, your tail needs to be past it.

Do you know whether or not multiple Hold Short lines is a method that's only used in the UK?


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Rick767
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RE: A Taxiway With "3" Hold Short Lines...Why?

Thu Mar 20, 2003 2:59 am

"If the runway is being operated under CAT II/III conditions, then there's likely a very low ceiling (200 AGL or lower), or fog, etc, and the farther back from the active you are, the better .... incase an arriving aircraft is off the centerline!"

The actual reason is to keep taxiing aircraft outside a calculated zone of interference. If they came forward to the CATI position their prescence may interfere with the localiser or glideslope signal (at a time when landing aircraft may be doing CATII/III Autolands onto the same runway). Like you said though, any increased separation with the runway is equally beneficial in low vis.

I'm sure you know this already but the solid line of a holding point is that which you must hold short of, so the centre holding point in that picture is obviously for aircraft vacating the runway at that intersection and holding short of the taxiway. The CAT II/III holding point is also a different pattern from the standard ones.
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Mr Spaceman
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RE: A Taxiway With "3" Hold Short Lines...Why?

Thu Mar 20, 2003 3:36 am

Hello Rick767.

There was another thought bouncing around in my head that I was thinking about and wanted to mention regarding the different line positions, but I couldn't get a grip on it. Your explanation was it. I've read about this before, regarding taxing aircraft interfering with the ILS signal if the Hold Short line is to close to the runway ..... thus the calculated distance of the lines from the runway to keep aircraft out of the "zone of interference" as you mentioned.

I'm sure it wouldn't be a pleasant experience for a flight crew to be gliding down the slope through dense fog to a DH of 200 ft AGL or lower, while hunting for any sign of the runway environment, then suddenly the ILS's localizer & glideslope signals go "haywire" because an aircraft on the ground taxied to close to the runway and caused interference.

I suspect that in a scenario like that, as a 767 pilot yourself, you wouldn't have much time to react and recover if your airliner's needles started chasing signals that were erratic!

What would you do? Perhaps quickly disconnect the autoland/autopilot and apply full throttle to go around. Have you practiced this scenario in a 767 simulator?


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cdfmxtech
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RE: A Taxiway With "3" Hold Short Lines...Why?

Thu Mar 20, 2003 3:42 am

All of the Flight Control Computers that I am familiar with do checks of the localizer sognal. If it senses erratic behavior of localizer and glideslope signals for long enough, the A/P will disconnect automatically.
 
Mr Spaceman
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RE: A Taxiway With "3" Hold Short Lines...Why?

Thu Mar 20, 2003 4:07 am

Hello Cdfmxtech.

Thank You for that information. That's pretty interesting to learn.

Obviously the Flight Control Computers would disconnect the A/P far enough out, as to give the pilots enough time to decide on whether or not to continue the approach while hand flying, or to go around and choose an option such as flying to an alternate airport where the ceilings are higher, etc, etc.

> Rick767, do you have regulations, company policy or perhaps personal limits which govern how low you would "hand fly" a 767/757 while in IMC ..... even if the winds were calm?


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