Go Back  PPRuNe Forums > Ground & Other Ops Forums > ATC Issues
Reload this Page >

CTOT/Slot vs. Taxi Prediction

ATC Issues A place where pilots may enter the 'lions den' that is Air Traffic Control in complete safety and find out the answers to all those obscure topics which you always wanted to know the answer to but were afraid to ask.

CTOT/Slot vs. Taxi Prediction

Old 5th Jul 2017, 11:50
  #1 (permalink)  
Thread Starter
 
Join Date: Jul 2014
Location: England
Posts: 77
CTOT/Slot vs. Taxi Prediction

Hi Guys,

I was recently thinking about this and after giving it a bit of a Google, I didn't seem to come up with much of an answer.

Say a flight at LHR is given a CTOT of 09:30 by the EuroControl CFMU, is it the pilot's responsibility to estimate the taxi-time to ensure that he can be ready for take-off within the 15-minute window?

My main area of confusion comes by the fact that airports such as LHR etc. can have huge taxi queues and delays, so who's job is it to ensure an aircraft compensates for taxi-time to ensure it pushes back from the gate with enough time to be -5/+10 CTOT?

Thanks in advance!
GetTheQRH is offline  
Old 5th Jul 2017, 13:03
  #2 (permalink)  
 
Join Date: Aug 2012
Location: FL390
Posts: 149
As a pilot I always ask ATC the current taxi time and earliest startup time.
737aviator is offline  
Old 5th Jul 2017, 13:41
  #3 (permalink)  
 
Join Date: Nov 2009
Location: Poland
Posts: 127
I don't know how is it done at LHR, but my guess is to report ready for startup as soon as you are. Then it is ATC responsibility to deal with your estimated taxi time.
samotnik is offline  
Old 5th Jul 2017, 15:58
  #4 (permalink)  
 
Join Date: May 2000
Location: Scotland
Posts: 260
The CTOT is based on your filed off-blocks time (EOBT), plus a nominal taxi time which is usually pre-set by the departure airport. For example, if you have filed EOBT at 0900 and the airport uses a 20-min taxi time, a zero-delay CTOT will be 0920. A 15-minute delay due, for example, to weather or capacity at destination [or any other reason, in fact] would result in a CTOT of 0935.

The taxi time might be varied by local ATC - for example, due to WIP, LVPs or congestion, it might take up to 30 minutes to get you to the runway. The taxi time might be increased in this case to avoid lots of missed slots.

Everything is based on you being ready to push back on your EOBT: that's all you have to do! Let local ATC sort out all the taxi timings etc.
NudgingSteel is offline  
Old 5th Jul 2017, 16:51
  #5 (permalink)  
 
Join Date: Dec 1999
Location: LHR/EGLL
Age: 41
Posts: 4,316
At an A-CDM airport (such as LHR) the taxi time will not be a blanket value, but will depend upon your stand/parking location, aircraft type, runway in use, and time of year, perhaps also modified by your particular airline. This is the VTT (Variable Taxi Time)

At such an airport the CTOT will be based on your TOBT+VTT+runway holding point buffer (if any). As long as you've called ready within the TOBT tolerance, that's your job done.

Call ready as soon as you are ready, that's all you can do.
Gonzo is online now  
Old 6th Jul 2017, 00:35
  #6 (permalink)  
 
Join Date: Jun 2002
Location: Wor Yerm
Age: 63
Posts: 0
Airports like LHR are not the problem. They want you gone ASAP. But other airports like AMS appear to do all they can to foul up your schedule. Typically, you start with a delay and it carries on throughout the day, regardless of traffic. On on-time is virtually impossible. Unfortunately they are not unique.

PM
Piltdown Man is offline  
Old 6th Jul 2017, 08:38
  #7 (permalink)  
 
Join Date: Feb 2006
Location: Rapunzel's tower
Posts: 445
Ideally call for start a few minutes prior to EOBT...at peak times, however, this is unlikely if there have been, say, weather regs all around the patch.
If the CTOT delay is 0 minutes and pilot calls for start after EOBT then ATC will assess whether aircraft can still make the CTOT.

The CTOT time should be regarded as the time aircraft are #1 at the holding point and ready for departure.
The CTOT window (-5 to +10mins) is for ATC to best manage departure order (e.g. departure routes, aircraft speed groups, wake turbulence).
It's not uncommon at "smaller" airports (with short taxi times, e.g. 5-10mins) when delays are present, that pilots request start just before CTOT with an expectation that they can be airborne before CTOT+10.
If there is no other traffic ATC might take the risk and give start approval at/just before CTOT (3-4minutes to start + 5minute taxi + 1minute to line-up and depart = 9 or 10minutes).
In all likelihood though there will be other traffic, there will be taxiway delays, there will be a number of other aircraft which have called in good time to make their CTOTs, etc, etc.

So, ideally call for start just before EOBT (but only call if you are actually ready!).
In practice call for start by CTOT minus the taxi time minus a few minutes for start up. That way ATC should have at least 10 minutes of "slack" for unexpected delays and to juggle the departure order to achieve the most efficient operation.
The most important thing is that if you know you're not going to be able to make CTOT (do not rely on CTOT+10) get a DLA message in early. The earlier you can adjust your expected EOBT the better the result will be for your new CTOT. If you leave it to the last moment and ATC refuse your start the likelihood is you'll get a pretty hefty CTOT delay.
good egg is offline  
Old 1st Aug 2017, 15:04
  #8 (permalink)  
 
Join Date: Aug 2017
Location: Globe
Posts: 1
And I would like to add always keep your EOBT updated according to Eurocontrol requirements. Any change to you EOBT for a period greater than 15 min before or after your EOBT must be communicated.

With an EOBT 0900 in an aerodrome with 10min taxitime a CTOT of 0910 is considered a No delay. But if you are ready for startup at 0835 (meaning roughly a 0840 off blocks) then you will perceive the CTOT as a delay.

Always keep in mind that a REA message will be rejected automatically by the NM if it is received earlier than EOBT-15min. I think that is an incentive for AOs to keep their EOBTimes updated.
Dionys is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.