Taxiway centre line off a runway, lead on or lead off?

[Pin Head]

For performance and professionality, are yellow taxiway centrelines for lead on or lead off purposes?

I always thought the latter as you need help in getting off in a hurry rather than getting on. It also gives you an excuse to make a smooth 90 turn on and use all runway rather than a slow gradual kind of sweep if you follow the centreline in most instances.

A reference would be really useful too.

Thank you.

[B737900er]

Best get your PPL books out and have read.

[Pin Head]

Hi

I have but can't see a reference.

Please help.

[Intruder]

Both. FAA AIM 2-3-4:b. Taxiway Centerline.
1. Normal Centerline. The taxiway centerline is a single continuous yellow line, 6 inches (15 cm) to 12 inches (30 cm) in width. This provides a visual cue to permit taxiing along a designated path. Ideally, the aircraft should be kept centered over this line during
taxi. However, being centered on the taxiway centerline does not guarantee wingtip clearance with other aircraft or other objects.

Note that SMGCS lighting (green lights) will overlie the yellow lines (AC 120-57A).

[Pin Head]

Think I have it;

5.2.8.1 Taxiway centre line marking shall be provided on a paved taxiway, de-icing/anti-icing facility and apron where the code number is 3 or 4 in such a way as to provide continuous guidance between the runway centre line and aircraft stands.

So starting off on the runway centre line, LEAD OFF to the aircraft stands??

[Pin Head]

But then again are they lead off??

http://www.aaib.gov.uk/cms_resources.cfm?file=/Boeing%20737-436,%20G-DOCT%2006-07.pdf

[B737900er]

For someone with over 2000 hours on B737 alone your questions worry me and a lot of posters on here.

[Pin Head]

But we have contradicting words here!

Which is right!

RTFQ or in this case RTFA

[Pin Head]

Yes I agree but the fairly well respected UK CAA was hinting that they are also lead on?

[Pin Head]

I agree but the report says the lines which are not at 90 degrees are referred to as lead on/lead off.

Tax way W at Aberdeen A rport requ red a turn through slightly more than 90o to line up with the centrel ne of Runway 6.

Thank you.

[Musket90]

Interesting question. The taxiway markings at a runway/taxiway intersection are considered mainly for lead-off purposes so ensuring a vacating aircraft following the marking doesn't leave the paved surface. The markings do serve as lead-on guidance for take-off but often once the aircraft goes beyond the holding point onto the runway pilots deviate from the line to reduce the line-up allowance knowing there should be sufficient pavement runway width to do this safely. Airports should bear this in mind when designing blast pads at runway ends to ensure they are secure and can cope with the increased jet blast from this type of manoeuvre.

[AerocatS2A]

I agree but the report says the lines which are not at 90 degrees are referred to as lead on/lead off.

Tax way W at Aberdeen A rport requ red a turn through slightly more than 90o to line up with the centrel ne of Runway 6.

Thank you.

The report says they are colloquially known as lead on/lead off lines. It is an everyday name given to the lines, it is not an instruction on how to use them!

This line is variously described colloquially as the ‘lead on’ or ‘lead off’ line depending on whether an aircraft is entering or vacating a runway

If you follow them to line up and you are performance limited then you have probably just invalidated your performance calculations. If you've done your performance from a more limiting intersection, then sure, use them as lead on lines.

[FlightDetent]

Line up allowance for loss in turn from 90° TWY is in the region of 14 meters on A320 family. And the performance figures are based on that number.

[noflynomore]

I think what the OP is asking in a roundabout way is where is an intersection TODA is measured from, an imaginary intersection of an (extended) taxiway centreline and the runway centreline or where the yellow taxi line eventually meets the Rwy centreline which is somewhat shorter, for those willing to gamble with an odd 10 metres or so in their t/o performance calcs.
The inelegant and uncomfortable swerve away and swerve back again line-up manoeuvre is a sign to me that either margins have been left too short (requiring more distance or more thrust) or the crew disn't look at the excess runway available.

In my old company it was endemic but few could rationalise why it was needed.

It also puzzles the hell out of ATC and following traffic who thought you'd been cleared for an intersection departure only to see you turning back towards the threshold.

[Driver 170]

Not a certified pilot but in no way do you use the yellow taxi line when entering a runway to line up.

Its kind of worrying you don't know this and even more frightening if your performance is based on this runway entry and you are at your Takeoff field length limit weight :(

[Intruder]

Not a certified pilot but in no way do you use the yellow taxi line when entering a runway to line up.
So, then, what do you do in Cat II or Cat III visibility, when using SMGCS lighting, which follows those yellow lines?

[Driver 170]

Are they available at any Europe airports or even any Europe based airlines?

[Chesty Morgan]

The only time I follow the yellow line during line up is in low vis.

[Driver 170]

Is that incase if you try to do a 90* turn you could end up off the runway?

[FlightDetent]

So, then, what do you do in Cat II or Cat III visibility, when using SMGCS lighting, which follows those yellow lines?
Given the fact that LVTO requires mnm of 125 m RVR, easily taxi trough 90 deg turn using Mk I eyeball. LVP does not magically improve the ASDA/TODA/TORA over what's calculated by the flight ops engineering folk.

The green-yellow coded runway turnoff light are simply ignored just as they are in good vis.

[Driver 170]

Doesn't aerodromes that are approved for Low Visibility Operations have a stop bar and lead on lights?