HANKE-Aviation GmbH - Flight Crew Training

CHAPTER 5 - Oceanic ATC Clearance

GENERAL

Oceanic Clearances are required for all flights within the NAT Airspace at or above FL55. Pilots should request Oceanic Clearances from the ATC unit responsible for the first OCA within which they wish to operate, following the procedures and the time-frame laid down in appropriate AIPs. Such clearances, although in most cases obtained some time before reaching the Oceanic entry point, are applicable only from that entry point. It is recommended that pilots should request their Oceanic Clearance at least 40 minutes prior to the Oceanic entry point ETA and, if requesting an OTS track, should include the next preferred alternative.

When requesting an oceanic clearance the pilot should notify the OAC of the maximum acceptable flight level possible at the boundary, taking into account that a climb to the assigned oceanic flight level must normally be achieved whilst the aircraft is within radar coverage. The pilot should also notify the OAC of any required change to the oceanic flight planned level, track or Mach Number as early as practicable after departure to assist the OAC in pre-planning optimum airspace utilization.

Methods of obtaining Oceanic Clearances include:

(1) use of published VHF clearance delivery frequencies;

(2) by HF communications to the OAC through the appropriate aeradio station (at least 40 minutes before boundary/entry estimate);

(3) a request via domestic or other ATC agencies;

(4) by data link, when arrangements have been made with designated airlines to request and receive clearances using on-board equipment. This method of Oceanic Clearance delivery is only possible from participating OACs with the necessary means of automation. Detailed procedures for its operation may vary.

At some airports situated close to oceanic boundaries, the Oceanic Clearance must be obtained before departure (e.g. from Prestwick, Shannon, Glasgow, Dublin, Belfast, Gander, Goose Bay).

If an aircraft, which would normally be RVSM and/or MNPS approved, encounters whilst en-route to the NAT Oceanic Airspace, a critical in-flight equipment failure, or at dispatch is unable to meet the MEL requirements for RVSM or MNPS approval on the flight, then the pilot must advise ATC at initial contact when requesting Oceanic Clearance.

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 jeopardize planned separation between aircraft, thus resulting in reclearance to a less economical track/flight level for the complete crossing; any such failure may also penalize following aircraft.

If the oceanic route on which the flight is cleared differs from that originally requested and/or the oceanic flight level differs from the current flight level, the pilot is responsible for obtaining the necessary domestic reclearance to ensure that the flight is in compliance with its Oceanic Clearance when entering oceanic airspace.

There are three elements to an Oceanic Clearance: route, Mach Number and flight level. These elements serve to provide for the three basic elements of separation: lateral, longitudinal and vertical.

The Oceanic Clearance issued to each aircraft is at a specific flight level and cruise Mach Number. Flight level or Mach Number changes should not normally be made without prior ATC clearance.

Prior to reaching the Shanwick OCA boundary, if pilots have not received their Oceanic Clearance then they are to remain clear of Oceanic Airspace whilst awaiting such Clearance. This is not the case for other NAT OCAs into any of which flights may enter whilst pilots are awaiting receipt of a delayed Oceanic Clearance.

An example of a pilot voice request for Oceanic Clearance is as follows:

"ACA 865 request Oceanic Clearance. Estimating 56N010W at 1131. Request Mach decimal eight zero, Flight Level three five zero, able Flight Level three six zero, second choice Track Charlie".

If the request also includes a change to the original flight plan, affecting the OCA, then it should be according to the following example:

"BAW 123 request Oceanic Clearance. Estimating 55N010W at 1147. Request Mach decimal eight zero, Flight Level three four zero. Now requesting Track Charlie, able Flight Level three six zero, second choice Track Delta".

CONTENTS OF CLEARANCES

An abbreviated clearance is issued by Air Traffic Services when clearing an aircraft to fly along the whole length of an Organized Track, or along a Polar Track within the Reykjavik CTA and/or Bodø OCA. When an abbreviated clearance is issued it includes:

Procedures exist for an abbreviated read back of an Oceanic Clearance issued on VHF. A typical example of such a clearance is as follows:

"ACA865 is cleared to Toronto via Track Bravo, from 56N010W maintain Flight Level three five zero, Mach decimal eight zero".

The flight crew will confirm that they are in possession of the current NAT Track message by using the TMI number in the read-back of the Oceanic Clearance, as follows:

"ACA865 is cleared to Toronto via Track Bravo 283, from 56N010W maintain Flight Level three five zero, Mach decimal eight zero".

If the TMI number is included in the read-back there is no requirement for the pilot to read back the NAT Track co-ordinates even if the cleared NAT Track is not the one which was originally requested. If any doubt exists as to the TMI (see fuller explanation of this term in Chapter 2) or the NAT Track co-ordinates, the pilot should request the complete track co-ordinates from the OAC. Similarly, if the pilot cannot correctly state the TMI, the OAC will read the cleared NAT Track co-ordinates in full and request a full read back of those co-ordinates.

For aircraft cleared by Shanwick OAC on random routings in the NAT Region the present procedure of reading the full track co-ordinates as part of the Oceanic Clearance and requesting from the pilot a full read back of the co-ordinates is expected to continue. Gander and Reykjavik OACs may, however, issue clearances for random routings which specify "via flight plan route". Nevertheless, in all circumstances regarding random route clearances, pilots are required to read back the full track co-ordinates of the flight plan route, from the oceanic entry point to the exit point.
 

OCEANIC CLEARANCES FOR FLIGHTS INTENDING TO OPERATE WITHIN THE NAT REGION AND SUBSEQUENTLY ENTER THE EUR OR NAM REGIONS

Oceanic Clearances issued to most flights in this category are strategic clearances intended to provide a safe separation for each flight, from oceanic entry to oceanic track termination point. Should a pilot receive a clearance on a track other than originally flight planned, special caution should be exercised to ensure that the co-ordinates of the assigned track and of the associated landfall and domestic routings are fully understood and correctly inserted into the automated navigation system. Appropriate cross checks should be carried out. In all cases when an en-route reclearance is requested, the pilot should ensure that the revised ATC clearance includes the new routing from the oceanic exit point to the first landfall point or coastal fix. If at the time of being given a clearance or reclearance, the pilot has any doubt, details should be checked with the ATC unit issuing the clearance/reclearance.

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.

ERRORS ASSOCIATED WITH OCEANIC CLEARANCES

Navigation errors associated with Oceanic Clearances fall into several categories of which the most significant are ATC System Loop errors and Waypoint Insertion errors.
 

ATC System Loop Errors

An ATC system loop error is any error caused by a misunderstanding between the pilot and the controller regarding the assigned flight level, Mach Number or route to be followed. Such errors can arise from incorrect interpretation of the NAT Track Message by dispatchers, errors in co-ordination between OACs, or misinterpretation of Oceanic Clearances or reclearances by pilots. Errors of this nature, which are detected by ATC from pilot position reports will normally be corrected. However, timely ATC intervention cannot always be guaranteed, especially as it may depend on HF communications.

Waypoint Insertion Errors

Experience has shown that many of the track keeping errors which occur result from:

More detailed guidance on this subject is contained in Chapters 9, 14 and 15 of this Document.

Many of the navigation error occurrences are the product of one or both of these causes. It is therefore extremely important that pilots double check each element of the Oceanic Clearance on receipt, and at each waypoint, since failure to do so may result in inadvertent deviation from cleared route and/or flight level.

(C) HANKE-Aviation GmbH 2014