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Transition level
During the approach briefing, crews should note the transition level on the approach plate or verified
by ATIS. Crews must be diligent when descending through the transition level to reset the altimeters
to QNH. This is particularly important when encountering IFR, night or high terrain situations. Any
confusion between a QNH set with inches of Mercury or hPa must be clarified.
NORTH ATLANTIC MNPSA OPERATIONS MANUAL CHAPTER 12
NAT MNPS 79 Edition 2009
Destination/block in
Navigation Accuracy Check
When arriving at the destination gate, crews should note any drift or circular error in the LRNS. A
GPS Primary Means system normally should not exceed 0.27NM for the flight. Some inertial
systems may drift as much as 2NM per hour. Because the present generation of LRNSs is highly
accurate, operators should establish a drift tolerance which if exceeded would require a write-up in
the Maintenance Log. RNP requirements demand that drift be closely monitored.
RVSM write-ups
Problems noted in the altimetry system, altitude alert or altitude hold must be noted in the
Maintenance Log. The RVSM airspace is closely monitored for any Height Deviations. An aircraft
not meeting the strict RVSM standards must not be flight-planned into RVSM airspace without
corrective action.
NORTH ATLANTIC MNPSA OPERATIONS MANUAL CHAPTER 13
NAT MNPS 80 Edition 2009
Chapter 13: Guarding Against Complacency
13.1 INTRODUCTION
13.1.1 Since 1977, when the MNPS rules were introduced, careful monitoring procedures have
provided a good indication both of the frequency with which navigation errors occur and their causes. Their
frequency is low: only one flight in around ten thousand commits a serious navigation error. However
because of the accuracy and reliability of modern navigation systems, the errors which do occur are most
often seen to be as a result of aircrew error.
13.1.2 Operational errors in the vertical plane also occur. Aircraft are sometimes flown at levels
other than those for which ATC clearance has been issued. In preparation for the introduction of RVSM in
the NAT Region (1997) a comprehensive data collection programme for vertical deviations was
implemented, together with an annual assessment of the resulting collision risks. As in the horizontal plane,
the frequency of vertical errors is low. However, the potential risk of even a single incidence of flying at an
uncleared level can be very significant. Currently, the NAT MNPSA risk estimates in the vertical plane, as a
result of operational errors or uncleared departures from flight level, exceed those arising from lateral gross
navigation errors.
13.1.3 It is therefore essential that crews do not take modern technology for granted. They should
at all times, especially during periods of low workload, guard against complacency and over-confidence, by
adhering rigidly to approved cockpit/flight deck procedures which have been formulated over many years, in
order to help stop operational errors from being an inevitability.
13.1.4 This chapter lists some of the errors that have been recorded in the NAT during recent years.
Also the NATSPG commissioned the UK National Air Traffic Services to produce an interactive DVD
ROM, “On the Right Track”, which highlights many of the common errors and discusses their causes. The
DVD ROM additionally contains general information on Air Traffic Control in the North Atlantic Region.
The DVD ROM, like this Manual, is aimed at pilots, dispatchers and others concerned in operations on the
North Atlantic. It is available at no charge to bona fide operators on application to:
customerhelp@nats.co.uk. Furthermore, an Oceanic Errors Safety Bulletin is available for downloading
from the ICAO EUR/NAT website (http://www.paris.icao.int/ )and is updated every 6 months. This is
currently augmented by a NAT Safety Alert. It is suggested that pilots consult these sources regularly.
13.2 OPERATIONAL HEIGHT ERRORS
13.2.1 The most common height errors are caused by:
a) executing an uncleared climb.
e.g. the crew of an aircraft entering Reykjavik OCA from Edmonton FIR encountered HF
Blackout conditions prior to reaching the Reykjavik OCA boundary and before receiving an
Oceanic Clearance. During the subsequent more than two hours of flight in the MNPSA, the
crew executed two step climbs before re-establishing contact with ATC.
Aircraft following an ATC clearance are assured of separation from other potentially conflicting
traffic. In HF Blackout conditions if an aircraft unilaterally changes level, ATC has no means to
advise or intervene with other traffic and separation can no longer be assured. In such a
circumstance, if a climb without ATC clearance is imperative then this should be treated as a
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