North Atlantic Tracks & Gross Navigational Errors

[zoink]

would anybody have any links that explain Gross Navigational Errors on NATs? Is there a CAA or FAA reference that I could use to determine the process for how they are monitored or reviewed?

I've found some material via google on events which led to a GNE but I'm looking for the laws or what ATC guys are taught..

Many thanks
zoink..

[G-OFUK]

A GNE is defined as one of the following (at least in Shanwick airspace):

An observation which differs from a report by 25nm or more laterally,
An observation which differs from an estimate passed by Shawick by 25nm or more laterally or
A report which differs from an estimate by 25nm or more laterally.

Responsibility for monitoring GNEs in NAT airspace is delegated to the North Atlantic Central Monitoring Agency (NAT CMA), you can read a bit about them here:
CMA (http://www.nat-pco.org/monitor.htm)

Hope that helps.

[zoink]

this is perfect. thank you G-OFUK!!

[rab-k]

In addition to the above, Shanwick procedures and the NATCMA requires any occasion where ATC takes action to prevent a GNE to be logged. Such "Interventions to Prevent GNEs" are far more frequent than actual GNEs and crews often don't realise that the very act of stating an intention to route to a position not specified in the Oceanic Clearance will result in reporting action being taken.

[WhatMeanPullUp]

rab-k

Oceanic airspace is patently more anally retentive nowadays than it was when I worked it if every error has reporting action taken on it. H/F comms are diabolical, the pilot reports his current position, his estimate for the next position and then the subsequent position after that, the last one probably being the 'error'. Even if the pilot gives his next position as incorrect who is to say the pilot did that? Because H/F is so crap, perhaps Ballygirreen misheard it therefore it is not the pilots fault. Aircraft GPS systems are highly accurate, yearly, how many real GNE's occur, bearing in mind the volume of modern aircraft that fly trans-Atlantic? probably one or two.

[rab-k]

WhatMeanPullUp

You "worked" Oceanic? Then surely you would know that...


Confirmation is sought by ATC of any reported discrepancy between the cleared route and intended route prior to any corrective and subsequent reporting action being taken, precisely so as to discount any mis-hear due to poor HF. The exception to this being where the discrepancy is immediate, e.g. the crew reports at the Oceanic Entry Point stating they're routing to 55N020W when the cleared route is via 56N020W. In such circumstances, the delays in HF comms require that the cleared route be confirmed in the first instance, rather than confirmation of the crew's intentions; which will be done subsequent to the confirmation of route.

ADS Waypoint Event Contracts are commonplace in the NAT region and are needless to say not subject to the shortcomings of HF; the route held in the FMS being downlinked directly to ATC ensuring that any discrepancy is actual rather than perceived.
The most common reason for such occurrences is for the cleared route to differ from the flight planned route and for that difference, for whatever reason, not to be reflected in the FMS. GNEs are seldom as a result of failures on the part of the INS but rather what is programmed into the FMS. These account for the vast majority of GNEs and Interventions to Prevent GNEs.

The reason for such "anal" behavior as you put it is for procedures and training to be improved to the point that no GNEs occur. This is not only on the part of operators, who without the reporting procedure may well be oblivious to such events, but also ATC providers. In our case, we have altered the phraseology used for the issue of clearances whose route differs from that of the flight plan, and have also incorporate such indicators of reroutes in our automated clearance delivery system, in order to assist crews in ensuring that they fly the cleared route as opposed to the flight plan. The only means of identifying the need for such changes in RTF and datalink comms was via a reporting procedure overseen by the NAT CMA which highlighted the true extent of the problem.
Am I to assume that for an ATC provider or airline operator to turn a blind-eye to such things would be acceptable to you?

[WhatMeanPullUp]

No, not acceptable but I am not anal enough to go into the depths that you have done to reply to a basic response.