Guidance concerning Air Navigation in and above the NAT MNPSA
IN FLIGHT PROCEDURES
It is recommended that during the initial part of the flight, ground navaids should be used to
verify the performance of the LRNSs. Large or unusual ‘map shifts’ in FMS output, or other discrepancies in navigation data, could be due to inertial platform misalignment or initialisation errors. Position updates to the FMS will not correct these errors despite possible indications to the contrary. If such a situation is encountered when INS/IRS are the primary LRNSs then it would be unwise to continue into NAT MNPS Airspace. Pilots should consider landing in order to investigate the cause and then perhaps be in a position to
correct the problem.
It is recommended that a compass heading check be presented and the results recorded. This
check is particularly helpful when using inertial systems. The check can also aid in determining the most
accurate compass if a problem develops later in the crossing.
ATC Oceanic Clearance and subsequent Re-clearances
Where practicable, two flight crew members should listen to and record every ATC
clearance and both agree that the recording is correct. Any doubt should be resolved by requesting clarification from ATC. In the event that a re-clearance is received when temporarily only one pilot is on the flight deck. Any flight profile, mach number or routing changes should not be executed, nor should the Navigation or Flight Management Systems be updated, until the second pilot has returned to the Flight Deck and a proper cross-checking and verification process can be undertaken.
If the ATC oceanic cleared route is identical to the flight planned track, it should be drawn
on the plotting chart and verified by the other pilot.
If the aircraft is cleared by ATC on a different track from that flight planned, some
regulators strongly recommend that a new Master Document be prepared showing the details of the cleared track. Overwriting of the existing flight plan can cause difficulties in reading the waypoint numbers and the new co-ordinates. For this purpose, it is helpful if a blank pro-forma Master Document (flight plan) is carried with the flight documents. One flight crew member should transcribe track and distance data from the appropriate reference source onto the new Master Document pro-forma and this should be checked by another crew member. If necessary, a new plotting chart may be used on which to draw the new track. The new document(s) should be used for the oceanic crossing. If the subsequent domestic portion of the flight corresponds to that contained in the original flight plan, it should be possible to revert to the original Master
Document at the appropriate point.
Experience has clearly shown that when ATC issues an initial oceanic clearance that differs
from the flight plan, or subsequently during the flight issues a re-clearance involving re-routing and new waypoints, there is a consequential increase in the risk of errors being made. Indeed errors associated with re-clearances continue to be the most frequent cause of Gross Navigation Errors in the North Atlantic MNPS Airspace. Therefore, in both of these circumstances the situation should be treated virtually as the start of a new flight and the procedures employed with respect to the following, should all be identical to those
procedures employed at the beginning of a flight (see paragraph 8.3.18 above):
a) b) c) d)
copying the ATC re-clearance; amending the Master Document; loading and checking waypoints; extracting and verifying flight plan information, tracks and distances, etc.; and
NAT Doc 007