Greater Than 2 Minute Revised ETA's vs. ADS-C

2 minutes vs. 3 minutes… seems to be the most asked question since the change a few years back. It helps to keep the reason for this change in mind, ADS-C reporting. One of the ADS-C reporting parameters that ATC will set is "120sec". The contract parameters are mostly hidden from the operating pilot. Buried inside the FMS, there are displays that will allow a pilot to view exactly ATC has "Contracted" for with your FMC. ETA revisions of greater than 120 seconds is one of these triggers. With ADS_C reporting, voice reports are not required. Reporting is automatic thru ADS-C updating ATC anytime your “NEXT” estimated time of arrival is off by more than 120 seconds.

ICAO modified Annex 2 with Amendment #43 in 2012 with this newer 2 minute/120 second threshold so as to be consistent between voice and ADS-C reporting. That being said, some regulators describe this reporting requirement as "3 Minutes or greater" vice the “Greater than 2minutes” found in Annex 2. It is the same threshold… just described from the other end of the number line.

The Human Factors problem here is that most every pilot remembers the "Greater than +/- 3 minutes" from instrument training. From my view, the choice to use "3 Minutes or greater"  is poor. It too closely resembles the old definition and creates the confusion we see now. Worldwide reference documents add little consistency for a solution to this problem. Here are some examples:

ICAO Annex 2, Rules of the Air, Chapter 3, Paragraph 3.6.2.2

c. Change in Time Estimate: If the time estimate for the next applicable reporting point, flight information region boundary or destination aerodrome, whichever comes first, is found to be in error in excess of 2 minutes from that notified to air traffic services, or such other period of time as is prescribed by the appropriate ATS authority or on the basis of air navigation regional agreements, a revised estimated time shall be notified as soon as possible to the appropriate air traffic services unit.

Now from the other end of the number line…

NAT Document #007, North Atlantic Operations And Airspace Manual, Chapter 5, Paragraph 5.1.7

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, unless providing position reports via ADS-C, the pilot must pass a revised estimate to ATC.

Seems to work with the NAT Ops Bulletins

NAT Ops Bulletin 2014-002, Erosion Of Longitudinal Separation

1. When transmitting waypoint position reports via voice, crews must communicate to ATC any ETAs that change by 3 minutes or more. This is an ICAO requirement and the information is used to modify ground-based ATC flight tracking systems.

Does a two-way description help you understand?

FAA Aeronautical Information Manual, Chapter 5, Paragraph 5-3-3

(b) A corrected estimate at anytime it becomes apparent that an estimate as previously submitted is in error in excess of 2 minutes. For flights in the North Atlantic (NAT), a revised estimate is required if the error is 3 minutes or more.

Maybe the Canadians can make some sense of this…

TC “Canadian” AIM, Rule of the Air and Air Traffic Services, Paragraph 8.1  “NOTE”

If the time estimate for the next applicable reporting point differs from the previously reported estimate by 3 min or more, a revised estimated time should be reported to the appropriate ATS unit as soon as possible.

This is what the FAA inspectors are told to look for…

FAA Order 8900 FAA Safety Inspectors Handbook, Volume 7, Chapter 3, Paragraph 7-81,D.4

Time Errors (Estimated Time of Arrival (ETA)/Actual Time of Arrival (ATA) error). ICAO Annex 2 was amended in 2012 and now specifies a more stringent tolerance: “if the time estimate for the next applicable reporting point, flight information region boundary or destination aerodrome, whichever comes first, is found to be in error in excess of 2 minutes from that notified to air traffic services, or such other period of time as is prescribed by the appropriate ATS authority or on the basis of air navigation regional agreements, a revised estimated time shall be notified as soon as possible to the appropriate air traffic services unit.

This is what the FAA ATC is told to look for…

FAA ORDER 7110.82D, SUBJ: Reporting Oceanic Errors, Paragraph 8

d. Time Error. Occurs when an aircraft’s reported actual time of arrival (ATA) is more than 3 minutes before or after the estimated time of arrival (ETA). (For North Atlantic (NAT) the criteria is 3 minutes or more.)

Jeppesen does not help matters when they publish conflicting information.

Jeppesen Airways Manual, General, Enroute Chapter, Enroute Data-General, Page #277

Change in time estimate: if the time estimate for the next applicable report point, flight information region boundary or destination aerodrome, whichever comes first, is found to be in error in excess of three minutes from that notified to air traffic services, or such other period of time as is prescribed by the appropriate ATS authority or on the basis of air navigation regional agreements, a revised estimated time shall be notified as soon as possible to the appropriate air traffic services unit. Latter in the same Jeppesen publication on Page#852 Annex 2, paragraph 3.6.2.2 is quoted exactly as "Greater than 2 Minutes" With ADS-C reporting, voice reports are not required. Reporting is automatic thru ADS-C updating ATC anytime your “NEXT” estimated time of arrival is off by more than 120 seconds. The update goes straight into the ATC computer and then alerts the controller IF there are any conflicts. Trouble is operating pilots just have to trust the system because there is no evidence in the cockpit of this.

Yea, I don't like that part. So what's your answer...

Some operators will use FreeText to update ETA’s. This is a “NO” because it requires a manual computer input by the controller (human error inducing). 

You still have not answered my question...

I think that if an operator MUST have a record of action to update a revised ETA in a ADS-C active environment…use CPDLC FreeText and ask “Confirm Revised NEXT ETA”. It’s not in the book but, will make it alot less stressful for an operator to prove that you are keeping ATC advised as to your ETA revision if ever questioned. This operation will not induce a human error into an automated system.

Bottomline... 
  • 1. Point is when “Next ETA” is >120sec difference, update ATC
  • ​2. If ADS-C active, it is automatic (w/o pilot notification)
  • 3. If no ADS-C active, update via voice 
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