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Guidance concerning Air Navigation in and above the NAT MNPSA


Rare Causes Of Lateral Navigation Errors


To illustrate the surprising nature of things which can go wrong, the following are examples

of some extremely rare faults which have occurred:

  • a)

    the lat/long co-ordinates displayed near the gate position at one international airport were wrong.

  • b)

    because of a defective component in one of the INS systems on an aircraft, although the correct forward waypoint latitude was inserted by the crew (51°) it subsequently jumped by one degree (to 52°).

  • c)

    the aircraft was equipped with an advanced system with all the co-ordinates of the waypoints of the intended route already in a database; the crew assumed that these co-ordinates were correct, but one was not.

  • d)

    when crossing longitude 40°W westbound the Captain asked what co-ordinates he should insert for the 50°W waypoint and was told 48 50. He wrongly assumed this to mean 48°50'N at 50°00W (when it really meant 48°N 50°W ) and as a result deviated 50 NM from track.

  • e)

    the flight crew had available to them the correct co-ordinates for their cleared track, but unfortunately the data which they inserted into the navigation computer was from the company flight plan, in which an error had been made.

  • f)

    at least twice since 1989, longitude has been inserted with an error of magnitude of times 10.

    • e.

      g. 100°W instead of 10°W, or 5°W instead of 50°W. Because of low angles of bank, the aircraft departed from track without the crews being aware, and both lateral and longitudinal separations with other aircraft were compromised.

  • g)

    a crew based at and usually operating from London Heathrow was positioned at London Gatwick for a particular flight. One pilot inadvertently loaded the Heathrow co-ordinates into the INS, instead of those for Gatwick. This initialisation error was only discovered when the aircraft had turned back within the NAT after experiencing a GNE.

  • h)

    the pilot of a flight departing from the Caribbean area input the wrong departure airfield co- ordinates prior to departure. This error was discovered when deviation from cleared route seriously eroded separation with two other opposite direction aircraft.



Never relax or be casual in respect of cross-check procedures. towards the end of a long night flight.

This is especially important

  • Avoid casual R/T procedures. A number of GNEs have been the result of a misunderstanding between pilot and controller as to the cleared route and/or flight level. Adhere strictly to proper R/T phraseology and do not be tempted to clip or abbreviate details of waypoint co-ordinates.

Make an independent check on the gate position. Do not assume that the gate co-ordinates are correct without cross-checking with an authoritative source. Normally one expects co-

ordinates to be to the nearest tenth of a minute. Therefore, ensure that

hundredth, or in minutes and seconds. (Greenwich) Meridian, remember the risk

If the aircraft of confusing east

is near to and west.

the the

display is not to the Zero Degree E/W

  • Before entering Oceanic Airspace make a careful check of LRNS positions at or near to the

last navigation facility – or perhaps the last but one.

NAT Doc 007


Edition 2010

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