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Guidance concerning Air Navigation in and above the NAT MNPSA


continue into the NAT MNPSA at FL310. Separation was immediately lost with a preceeding aircraft at that flight level.

Crews are responsible for requesting and obtaining any domestic ATC clearance necessary to climb (or descend) to the initial flight level specified in their received Oceanic Clearance, prior to reaching the oceanic boundary. While adjacent ACCs generally use their best endeavours to get an aircraft to it's oceanic level before the boundary, it must be recognized that entry into NAT MNPSA at the cleared oceanic level is entirely the responsibility of the crew. It does appear from the relative frequency of this type of error that this is not widely understood. It should also be appreciated that such requests must be made sufficiently early to allow the domestic ATC unit time to respond.

  • f)

    An occasional error is to fly at one (uncleared) level and report at the (different) cleared level !

  • e.

    g. the crew of a major airline reported at FL360 (the cleared level), all the way across the

ocean but were in fact flying at FL350!! They had been cleared to cross 40°W at FL360 and correctly entered the cleared level into the FMC but did not execute the command prior to 40°W. During position reporting the aircraft level was reported by reference to the FMC altitude hold box.

Without SSR ATC must rely upon crew position report data to plan for the safe separation of all traffic. If any such data is in error actual separations can be compromised.



More Common Causes Of Lateral Navigation Errors

14.3.1 follows:

The most common causes of GNEs, in approximate order of frequency, have been as

  • a)

    having already inserted the filed flight plan route co-ordinates into the navigation computers, the crew have been re-cleared by ATC, or have asked for and obtained a re-clearance, but have then omitted to re-program the navigation system(s), amend the Master Document or update the plotting chart accordingly.

  • b)

    a mistake of one degree of latitude has been made in inserting a forward waypoint. There seems to be a greater tendency for this error to be made when a track, after passing through the same latitude at several waypoints (e.g. 57°N 50°W, 57°N 40°W, 57°N 30°W) then changes by one degree of latitude (e.g. 56°N 20°W). Other circumstances which can lead to this mistake being made include receiving a re-clearance in flight.

  • c)

    the autopilot has been inadvertently left in the heading or de-coupled mode after avoiding weather, or left in the VOR position after leaving the last domestic airspace VOR. In some cases, the mistake has arisen during distraction caused by SELCAL or by some flight deck warning indication.

  • d)

    an error has arisen in the ATC Controller/Pilot communications loop, so that the controller and the crew have had different understandings of the clearance. In some cases, the pilot has heard not what was said, but what he/she was expecting to hear.

NAT Doc 007


Edition 2010

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