Guidance concerning Air Navigation in and above the NAT MNPSA
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, the pilot must 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.
If any of the route, flight level or Mach Number in the clearance differs from that flight
planned, requested or previously cleared, attention may be drawn to such changes when the clearance is delivered (whether by voice or by datalink). Pilots should pay particular attention when the issued clearance differs from the Flight Plan. (N.B. a significant proportion of navigation errors investigated in the NAT involve an aircraft which has followed its Flight Plan rather than its differing clearance).
Furthermore it must be recognised that if the entry point of 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 requesting and obtaining the necessary domestic re-clearance 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.
(See Chapter 7 for Application of Mach Number Technique.)
If pilots have not received their Oceanic Clearance prior to reaching the Shanwick OCA
boundary, they must contact Domestic ATC and request instructions to enable them 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. Pilots should always endeavour to obtain Oceanic Clearance prior to entering these other NAT OCAs; however if any difficulty is encountered the pilot should not hold while awaiting Clearance unless so directed by ATC. In such circumstances, pending receipt of the Oceanic Clearance, the aircraft should continue to maintain the
flight level cleared by the current control authority.
An example of a pilot voice request for Oceanic Clearance is as follows:
“ACA 865 request Oceanic Clearance. Estimating PIKIL 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 RESNO 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 Organised Track. When an abbreviated clearance is issued it includes:
which will normally be destination airfield;
NAT Doc 007