World Air Ops | NAT | Doc 007 MNPS Guidance

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Guidance concerning Air Navigation in and above the NAT MNPSA CHAPTER 14CHAPTER 14: GUARDING AGAINST COMPLACENCY14.1 INTRODUCTION14.1.1 Since 1977, when the MNPS rules were introduced, careful monitoring procedures haveprovided a good indication both of the frequency with which navigation errors occur and their causes. Theirfrequency is low: only one flight in around ten thousand commits a serious navigation error. Howeverbecause of the accuracy and reliability of modern navigation systems, the errors which do occur are mostoften seen to be as a result of aircrew error.14.1.2 Operational errors in the vertical plane also occur. Aircraft are sometimes flown at levelsother than those for which ATC clearance has been issued. In preparation for the introduction of RVSM inthe NAT Region (1997) a comprehensive data collection programme for vertical deviations wasimplemented, 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 anuncleared level can be very significant. Currently, the NAT MNPSA risk estimates in the vertical plane, as aresult of operational errors or uncleared departures from flight level, exceed those arising from lateral grossnavigation errors.14.1.3 It is therefore essential that crews do not take modern technology for granted. They shouldat all times, especially during periods of low workload, guard against complacency and over-confidence, byadhering rigidly to approved cockpit/flight deck procedures which have been formulated over many years, inorder to help stop operational errors from being an inevitability.14.1.4 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 DVDROM, “On the Right Track”, which highlights many of the common errors and discusses their causes. TheDVD 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 theNorth 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 downloadingfrom the ICAO EUR/NAT website (http://www.paris.icao.int/ )and is updated every 6 months. This iscurrently augmented by a NAT Safety Alert. It is suggested that pilots consult these sources regularly.14.2 OPERATIONAL HEIGHT ERRORS14.2.1 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 HFBlackout conditions prior to reaching the Reykjavik OCA boundary and before receiving anOceanic Clearance. During the subsequent more than two hours of flight in the MNPSA, thecrew executed two step climbs before re-establishing contact with ATC.Aircraft following an ATC clearance are assured of separation from other potentially conflictingtraffic. In HF Blackout conditions if an aircraft unilaterally changes level, ATC has no means toadvise or intervene with other traffic and separation can no longer be assured. In such acircumstance, if a climb without ATC clearance is imperative then this should be treated as acontingency and the appropriate track offset of 15 NM should be flown.NAT Doc 007 84 Edition 2010
Guidance concerning Air Navigation in and above the NAT MNPSA CHAPTER 14b) misinterpreting an ATC acknowledgement of a request as a clearancee.g. a crew requested a step climb from Shanwick OAC using HF Voice through the Shannonaeradio station. The radio operator acknowledged the request to the aircraft and forwarded itto the Shanwick controller for review and action. The crew interpreted the radio operator’sacknowledgement as an approval of the request and immediately executed the step climb. Thecontroller subsequently denied the request due to conflicting traffic with inadequatelongitudinal separation at the requested higher level. The requesting aircraft had reached thenew level and therefore violated separation minima before receiving the denial. Similarincidents have occurred during NAT CPDLC trials when crews have misinterpreted atechnical acknowledgement of a datalink request for an ATC approval.When DCPC is unavailable and air/ground ATS communications are via a third party (whether radiooperator or datalink service provider) crews must be aware that acknowledgements of requests donot constitute approval.c) not climbing or descending as clearede.g. a crew was cleared for a climb to cross 4030W at FL350. The crew mis-interpreted theclearance and took it to mean climb to cross 40°N 30°W (instead of 40° 30'W) at FL350.While this was caused by a seemingly ambiguous clearance, crews must be on their guard and querythe clearance if in any doubt. Crews should be aware of the risks of non-compliance with aclearance, or with a restriction within a clearance. A significant number of height deviations havebeen reported where an aircraft had been cleared to change level after the next route waypoint andhas done so immediately or has been cleared to change level immediately and had not done so until alater time. Both cases can very easily result in the loss of safe separation with other traffic. Suchinstances are often, but by no means exclusively, associated with misinterpretation of CPDLCmessage sets (a crew training/familiarity issue) whereby the words AT or BY are interpreteddifferently from their intended meaning. This is a problem particularly (but not exclusively) withcrew members whose first language is not English. It is compounded in the cases of languageswhich have no directly equivalent words to differentiate between AT or BY, or perhaps use the sameword for each (this is apparently true of a number of european languages, for example). The dangersassociated with misinterpretation of conditional clearances must be appreciated. If an aircraft climbsor descends too soon or too late it is almost inevitable that it will lose separation with the othertraffic, that was the reason for the condition being applied by ATC.d) not following the correct contingency procedurese.g. following an engine failure a crew descended the aircraft on track rather than carryingout the correct contingency procedures (see Chapter 12).Particularly when flying in the OTS, crews must appreciate that there is a significant likelihood ofconflict with other aircraft at lower levels unless the appropriate contingency offset procedure isadopted. (See paragraph 12.3.4)e) entering the NAT MNPSA at a level different from that contained in the received OceanicClearance.e.g. a crew flying through Brest FIR at FL310 en route to the Shanwick OCA boundaryreceived an oceanic clearance for FL330. The crew requested a climb from Brest but it hadnot been received when the aircraft reached the Shanwick boundary. The crew elected toNAT Doc 007 85 Edition 2010
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