Change to Oceanic time tolerance?

[RMC]

Relatively new to Oceanic operation and in my ground school the company instructor advised that if we have a Revised Time Over a waypoint of three minutes or more we have to advise ATC beforehand. Yesterday I was reading the Jeps. Orth Atlantic Orientation chart and in bold three times Two minutes was mentioned. Has this been a recent change....is my company out of date (or am I missing something). Thanks in advance.

[confused atco]

its the 2 minutes good and 3 min bad.
So if a time for the Oceanic boundary is 12:05.
We count the clearance window as
12:02:30 to 12:07:29.
not
12:02:01 to 12:07:59.

This will then cover the tolerance as per ICAO Annex 11 chapter 2.
2.25 Time in ATC.
2.25.3
Air traffic services unit clocks and other time-recording devices shall be checked as necessary to ensure correct time to within plus or minus 30 seconds of UTC.

[RMC]

Thanks for the reply CA. So if I understand you correctly that is two mins with a 30 second tolerance bolted on each end? I had not heard about a tolerance of 30 seconds before. Has this changed from the maximum deviation of 2mins 59 seconds?

[confused atco]

the maximum deviation of 2mins 59 seconds?
There in lies your problem.
It is not 59 seconds that is used its +- 30 seconds.
All clocks in ATC are synchronised to UTC.
One of the items you get on start up is a time check to ensure that you are synchronised too.

Take the following scenario
Your Oceanic Clearance is 1700 with a second aircraft procedurally separated 10 min (T & C's apply) behind.
It is possible for you to cross at 1702:29 with the following aircraft at 1707:30.
Separation is still ensured as this +_2 min is part of the safety buffer.

Using your interpretation you think that you should be allowed out at 1702:59 while the following aircraft crosses at 1707:01?

[RMC]

Clearance.​ ​ ​
Estimate for​ Oceanic​ Entry​ ​
After​ obtaining​ and reading​ back the​ clearance,​ the pilot​ should monitor​ the forward estimate​ ​
for​ oceanic entry,​ and if​ this changes​ by​ 3 minutes or​ more,​ should pass​ a revised estimate​ ​
to ATC.​ As planned longitudinal spacing​ by​ these OACs is based solely​ on the estimated​ ​
times​ over​ the oceanic​ entry​ fix​ or boundary,​ failure to adhere​ to​ this​ ETA amendment​ ​
procedure​ may​ jeopardise planned separation between aircraft, thus resulting in​ a ​
subsequent re-clearance to​ a​ less​ economical track/flight level for​ the​ ​ complete​ ​ crossing.​ ​
Any​ such failure may​ also penalise following​ aircraft..

This is what our manual says......is it out of date.....or was this never correct?

[confused atco]

You are confusing 2 things here.

You have a time restriction to meet.
This has a tolerance of +-2 minutes (and 30 seconds obviously).

If you cannot make this restriction then you are 3 minutes out which now requires a revision to be passed.

[RMC]

Thanks for sticking with me on this......I just checked the NAT doc 007 which I assumed to be the controlling document. This is where we get our three minutes or more from ....

Natdoc007 6.3.4 “Clearance.​ ​ ​

Estimate for​ Oceanic​ Entry​ ​

After​ obtaining​ and reading​ back the​ clearance,​ the pilot​ should monitor​ the forward estimate​ ​

for​ oceanic entry,​ and if​ this changes​ by​ 3 minutes or​ more,​ should pass​ a revised estimate​ ​

to ATC.​ As planned longitudinal spacing​ by​ these OACs is based solely​ on the estimated​ ​

times​ over​ the oceanic​ entry​ fix​ or boundary,​ failure to adhere​ to​ this​ ETA amendment​ ​

procedure​ may​ jeopardise planned separation between aircraft, thus resulting in​ a ​

subsequent re-clearance to​ a​ less​ economical track/flight level for​ the​ ​ complete​ ​ crossing.​ ​

Any​ such failure may​ also penalise following​ aircraft.”

my company interpretation of this has been 2 mins 59 seconds maximum to avoid missing by three minutes or more.

I know this is your area of expertise (and the Jeps chart backs up your two minutes) but we have conflicting information here (and no pilot is aware of the 30 second tolerance.....which is a good thing because if you tell us there is a tolerance we will too often use it to the max).

[confused atco]

I remember when we had 5 minutes not 2 :E
Time in ATC is dictated by the quote above from ANNEX 11.

I will talk of the Shannon/Shanwick interface as that is where I am familiar.
When entering the ocean from domestic airspace a number of things are happening.
The Oceanic controllers have arranged separation based on the estimated time over that you give.
We too receive a copy of the Oceanic Clearance,
Our job is to ensure that you enter the ocean in compliance with the assigned clearance.
If this is not possible we will liaise with the A/C and the Oceanic Controller to ensure separation is in place.

Either way you will enter the ocean separated from the A/C in front and behind.

When you log on to EGGX with CPDLC your avionics are updating them with your ACTUAL time over the point.
In this case your "use" of the tolerance is moot.

Modern avionics ensure more accurate position reports hence separation can be reduced (RLAT/RLONG and other wonderful acronyms).

[737aviator]

my company interpretation of this has been 2 mins 59 seconds maximum to avoid missing by three minutes or more.


My company interpretation is the same, our manuals say 179 seconds.

[RMC]

Thanks for the replies guys. I am going to write to my Chief Pilot (an ex ATCO) to ask him to review this aspect of our manuals. CA I see the time tolerance in Annex 11 but can’t find a reference to either two or three minutes. Pint of Guinness \ bottle of wine if you can help me out with that ?

[parishiltons]

Thanks for the replies guys. I am going to write to my Chief Pilot (an ex ATCO) to ask him to review this aspect of our manuals. CA I see the time tolerance in Annex 11 but can’t find a reference to either two or three minutes. Pint of Guinness \ bottle of wine if you can help me out with that ?
confused_atco is correct, and his/her references are valid. Anything greater 2m 30s is three minutes for the purposes you are referring to. Applies worldwide, not just in the Atlantic.

The same logic applies to holding and adjusting speed to cross a waypoint at a given time. A sequencing instruction to depart a holding fix or cross a waypoint at, say 0030 means any time between 0029 30 seconds, and 0030 29 seconds.

[RMC]

I would be more than Happy to take your word for it on the references......but my CP is from Germany and will be interested in which para of annex 11 refers to two mins plus or minus 30 seconds. ICAO 007 talks about three mins so there is a real danger that some people think it is three m8 s plus or minus 30 seconds.

[confused atco]

From Annex 11 Amendment 50B2.26 Time in air traffic services 2.26.1 Air traffic services units shall use Coordinated Universal Time (UTC) and shall express the time in hours and minutes and, when required, seconds of the 24-hour day beginning at midnight. 2.26.2 Air traffic services units shall be equipped with clocks indicating the time in hours, minutes and seconds, clearly visible from each operating position in the unit concerned. 2.26.3 Air traffic services unit clocks and other time-recording devices shall be checked as necessary to ensure correct time to within plus or minus 30 seconds of UTC. Wherever data link communications are utilized by an air traffic services unit, clocks and other time-recording devices shall be checked as necessary to ensure correct time to within 1 second of UTC.2.26.4 The correct time shall be obtained from a standard time station or, if not possible, from another unit which has obtained the correct time from such station. 2.26.5 Aerodrome control towers shall, prior to an aircraft taxiing for take-off, provide the pilot with the correct time, unless arrangements have been made for the pilot to obtain it from other sources. Air traffic services units shall, in addition, provide aircraft with the correct time on request. Time checks shall be given to the nearest half minute.



ICAO 007
Importance of Accurate Time 8.2.2 It must be recognised that proper operation of a correctly functioning LRNS will ensure that the aircraft follows its cleared track. ATC applies standard separations between cleared tracks and thereby assures the safe lateral separation of aircraft. However, longitudinal separations between subsequent aircraft following the same track and between aircraft on intersecting tracks are assessed in terms of differences in ETAs/ATAs at common waypoints. Aircraft clock errors resulting in position report time errors can therefore lead to an erosion of actual longitudinal separations between aircraft. It is thus vitally important that prior to entry into the NAT HLA the time reference system to be used during the flight is accurately synchronised to UTC and that the calculation of waypoint ETAs and the reporting of waypoint ATAs are always referenced to this system. Many modern aircraft master clocks (typically the FMS) can only be reset while the aircraft is on the ground. Thus the Pre-flight Procedures for any NAT HLA flight must include a UTC time check and resynchronisation of the aircraft master clock

[parishiltons]

I would be more than Happy to take your word for it on the references......but my CP is from Germany and will be interested in which para of annex 11 refers to two mins plus or minus 30 seconds. ICAO 007 talks about three mins so there is a real danger that some people think it is three m8 s plus or minus 30 seconds.
There's a lot of confusion about the two vs three minute thing. If you are calculating ETOs to the minute, then a change of three (or more) minutes would trigger a compulsory revision. From an ATC perspective, that means 'more than two minutes' as ATC records ETOs and positions ATO in whole minutes. If however your navigation system calculates ETOs to the second, then rounding kicks in as to whether a revised ETO is required to be reported to ATC. Let's say that your original ETO at a waypoint is 0030. You (or your onboard systems) determine that the ETO is now revised to 0032 and 29 seconds. That rounds to 0032 so there is no requirement to advise ATC of the revised ETO. If however your revised ETO is 0032 and 30 seconds, that rounds to 0033, and so must be passed to ATC as a revision. Hope that clears it up.

[RMC]

Excellent.....so as the aircraft calculates in fractions if a minute then two mins 59 seconds (or 2.9 mins on somej is what we use.

The next big related flight deck myth/ mystery is that if we have active ADS reporting we do not need to manually report a revision to our time over as the system does it automatically. Once again Jep documents appear to contradict this.

[parishiltons]

Excellent.....so as the aircraft calculates in fractions if a minute then two mins 59 seconds (or 2.9 mins on somej is what we use.

The next big related flight deck myth/ mystery is that if we have active ADS reporting we do not need to manually report a revision to our time over as the system does it automatically. Once again Jep documents appear to contradict this.



Assume you are referring to ADS-C here? If so then yes, the system does do it automatically. If your onboard ADS-C downlinks an ETO change that is >2min (call it 3 min - let's not get into that debate again!) it will trigger an ETO alert on the ATC system. ATC is then obliged to challenge your ETO at the next waypoint and potentially chastise you from not updating it. A typical example is if ATC has to use (say) a 10 minute longitudinal separation standard on the route you are flying. You are at a different level to traffic ahead or behind but (say) 12 minutes apart longitudinally. You then request a level change to the same level as the other traffic. ATC approves because the separation is 10 minutes or more. Once you make the level change you encounter different winds and your onboard system calculates a revised ETO at the next waypoint that provides less than 10 minutes separation from the other traffic. At the next scheduled ADS-C update the revised ETO is downlinked to ATC. The ATC system calculates that there is no longer at least 10 minutes between you and the other traffic. The ATC system starts creating alerts, the controller has a minor heart attack, you get a sudden level change and the paperwork starts. So yes, you need to be careful that your formal position reporting ETOs are not contradicted by what your ADS-C downlinks tell ATC.