HANKE-Aviation GmbH - Flight Crew Training



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 flights 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.

Operational errors in the vertical plane also occur. Aircraft are sometimes flown at levels other than those for which ATC clearance has been issued. 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 significant.

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 procedures which have been formulated over many years, in order to help stop operational errors from being an inevitability.


To illustrate the surprising nature of things which can go wrong, the following are examples of some extremely rare faults which have occurred:


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

Operational Height Errors

Most common height errors are caused by:

e.g. a crew was cleared for a climb to cross 4030W at FL350. The crew mis-interpreted the clearance and took it to mean climb to cross 40N 30W (instead of 40 30 W) at FL350.

While this was caused by a seemingly ambiguous clearance, crews must be on their guard and query the clearance if in any doubt.

e.g. following an engine failure a crew descended the aircraft on track rather than carrying out the correct contingency procedures (see Chapter 12).

e.g. the crew of a major airline reported at FL360 (the cleared level), all the way across the ocean but were in fact at FL350!! They had been cleared to cross 40W at FL360 and correctly entered the cleared level into the FMC but did not execute the command prior to 40W. During position reporting the aircraft level was reported by reference to the FMC altitude hold box.


Never relax or be casual in respect of the cross-check procedure; this is especially important towards the end of a long night flight.

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. 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 the display is not to the hundredth, or in minutes and seconds. If the aircraft is near to the Zero Degree E/W (Greenwich) Meridian, remember the risk of confusing east and west.

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.

Do not assume that the aircraft is at a waypoint merely because the alert annunciator indicates; cross-check by reading present position.

Flight deck drills. There are some tasks on the flight deck which can safely be delegated to one member of the crew, but navigation using automated systems is emphatically not one of them, and the Captain should participate in all navigation cross-check procedures.

Initialization errors. Always return to the ramp and re-initialize inertial systems if the aircraft is moved before the navigation mode is selected. If after getting airborne, it is found that during initialization a longitude insertion error has been made, unless the crew thoroughly understand what they are doing, and have also either had recent training on the method or carry written drills on how to achieve the objective, the aircraft should not proceed into MNPS Airspace, but should turn back or make an en-route stop.

Waypoint loading. Before departure, check that the following agree: computer flight plan, ICAO flight plan, track plotted on chart, and if appropriate, the track message. In flight, involve two different sources in the cross-checking, if possible. Do not be so hurried in loading waypoints that mistakes become likely, and always check waypoints against the current ATC clearance.

Use a flight progress chart on the flight deck. It has been found that making periodic plots of position on a suitable chart and comparing with current cleared track, greatly helps in the identification of errors before getting too far from track.

Consider making a simple use of basic DR Navigation as a back-up. Outside polar regions, provided that the magnetic course (track) is available on the flight log, a check against the magnetic heading being flown, plus or minus drift, is likely to indicate any gross tracking error.

Always remember that something absurd may have happened in the last half-hour. There are often ways in which an overall awareness of directional progress can be maintained; the position of the sun or stars; disposition of contrails; islands or coast-lines which can be seen directly or by using radar; radio nav-aids, and so forth. This is obvious and basic, but some of the errors which have occurred could have been prevented if the crew had shown more of this type of awareness.

If the crew suspects that equipment failure may be leading to divergence from cleared track, it is better to advise ATC sooner rather than later.

In conclusion, navigation equipment installations vary greatly between operators; but lessons learned from past mistakes may help to prevent mistakes of a similar nature occurring to others in the future.


The Prevention of Deviations From Track as a Result of Waypoint Insertion Errors


During the monitoring of navigation performance in the NAT MNPS Airspace, a number of GNEs are reported. (There were 24 in 1997 and 17 in 1998.) Such errors are normally detected by means of long range radars as aircraft leave oceanic airspace. Occasionally, potential errors are identified by ATC from routine aircraft position reports.

Investigations into the causes of all recent deviations show that about 75% are attributable to equipment control errors by crews and that almost all of these errors are the result of programming the navigation system(s) with incorrect waypoint data otherwise known as waypoint insertion errors.


Waypoint insertion errors can be virtually eliminated if all operators/crews adhere at all times to approved operating procedures and cross checking drills. This Manual provides a considerable amount of guidance and advice based on experience gained the hard way, but it is quite impossible to provide specific advice for each of the many variations of navigation systems fit.

The following procedures are recommended as being a good basis for MNPS operating drills/checks:

The procedures outlined in this Section will detect any incipient gross errors, providing that the recorded/plotted cleared route is the same as that provided by the controlling ATS authority. If there has been a misunderstanding between the pilot and controller over the actual route to be flown (i.e. an ATC loop error has occurred), then the last drill above, together with the subsequent passing of the position report, will allow the ATS authority the opportunity to correct such misunderstanding before a hazardous track deviation can develop.

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