INTRODUCTION

The aircraft navigation systems necessary for flying in NAT MNPS Airspace are capable of high-performance standards. However it is essential that stringent cross-checking procedures are employed, both to ensure that these systems perform to their full capabilities and to minimize the consequences of equipment failures and possible human errors.

Navigation systems are continuously evolving and early editions of this Manual concentrated on offering specific guidance on the use of individual systems. Rather than specifying the types of equipment required for flying in defined airspace, current thinking is moving towards specifying a Required Navigation Performance (RNP), in other words a track keeping capability. As an example, the navigation performance accuracy of the aircraft population operating in airspace designated RNP X airspace would be expected to be X nm on a 95% containment basis. The NAT MNPS inter alia defines a requirement for the standard deviation of lateral track errors to be less than 6.3 nm. This effectively equates to an RNP value of 12.6 nm - or two standard deviations. (For more detailed information on RNP and MNPS see the following ICAO Documents: Doc 9613 – ‘Manual on Required Navigation Performance’ and NAT Doc 001 – ‘Consolidated Guidance Material North Atlantic Region’.)

Obviously, there are several combinations of airborne sensors, receivers, computers with navigation data bases and displays which are capable of producing like accuracies, with inputs to automatic flight control systems giving track guidance. However, regardless of how sophisticated or mature a system is, it is still essential that stringent navigation and cross checking procedures are maintained if Gross Navigation Errors (GNEs) are to be avoided.

Note: a GNE within NAT Airspace is defined as a deviation from cleared track of 25 nm or more. These errors are normally detected by means of long range radars as aircraft leave oceanic airspace. Such errors may also be identified through the scrutiny of routine position reports from aircraft.

The procedures listed in this Chapter are not intended to be equipment specific and may not all be pertinent to every aircraft. For specific equipment, reference should be made to Manufacturers' and operators' handbooks and manuals.

There are various references in this material to two pilots; however when carried, a third crew member should be involved in all cross check procedures to the extent practicable. Maintenance of a high standard of navigation performance is absolutely essential to the maintenance of safety in the NAT MNPS Airspace.
 

GENERAL PROCEDURES

Importance of Accurate Time

It must be recognized that proper operation of a correctly functioning LRNS will ensure that the aircraft follows its cleared track. ATC applies standard separations between cleared tracks and thereby assures the safe lateral separation of aircraft. However, longitudinal separations between subsequent aircraft following the same track and between aircraft on intersecting tracks are assessed in terms of differences in ETAs/ATAs at common waypoints. Aircraft clock errors resulting in position report time errors can therefore lead to an erosion of actual longitudinal separations between aircraft. It is thus vitally important that prior to entry into the NAT MNPS Airspace the time reference system to be used during the flight is accurately synchronized to UTC and that the calculation of waypoint ETAs and the reporting of waypoint ATAs are referenced to this system. Many modern aircraft master clocks can only be reset while the aircraft is on the ground. Thus the Pre-flight Procedures for any NAT MNPS flight must include a UTC time check and resynchronization of the aircraft master clock. Lists of acceptable time sources for this purpose have been promulgated by NAT ATS Provider States.

The following are examples of acceptable time standards:

Further details of these and other acceptable time references can be found in AIS documentation of the NAT ATS Provider States. In general, any other source of UTC, that can be shown to the State of the Operator or the State of Registry of the aircraft to be equivalent, may be allowed for this purpose.
 

The Use of a Master Document

Navigation procedures must include the establishment of some form of master working document to be used on the flight deck. This document may be based upon the flight plan, navigation log, or other suitable document which lists sequentially the waypoints defining the route, the track and distance between each waypoint, and other information relevant to navigation along the cleared track. When mentioned subsequently in this guidance material, this document will be referred to as the 'Master Document'.

Misuse of the Master Document can result in GNEs occurring and for this reason strict procedures regarding its use should be established.

These procedures should include the following:

• only one Master Document to be used on the flight deck. However, this does not preclude other crew members maintaining a separate flight log.

• on INS equipped aircraft a waypoint numbering sequence should be established from the outset of the flight and entered on the Master Document. The identical numbering sequence should be used for storing waypoints in the navigation computers.

• for aircraft equipped with FMS data bases, FMS generated or inserted waypoints should be carefully compared to Master Document waypoints and cross checked by both pilots.

• an appropriate symbology should be adopted to indicate the status of each waypoint listed on the Master Document.

The following is a typical example of Master Document annotation. An individual operator’s procedures may differ slightly but the same principles should be applied:

• the waypoint number is entered against the relevant waypoint co-ordinates to indicate that the waypoint has been inserted into the navigation computers.

• the waypoint number is circled, to signify that insertion of the correct co-ordinates in the navigation computers has been double-checked independently by another crew member.

• the circled waypoint number is ticked, to signify that the relevant track and distance information has been double-checked.

• the circled waypoint number is crossed out, to signify that the aircraft has overflown the waypoint concerned.

All navigational information appearing on the Master Document must be checked against the best available prime source data. When a reroute is necessary, it is recommended that a new Master Document is prepared for the changed portion of the flight. If the original Master Document is to be used the old waypoints should be clearly crossed out and the new ones entered in their place.

When ATC clearances or reclearances are being obtained, headsets should be worn, because the inferior clarity of loud-speakers has, in the past, caused errors during receipt. Two qualified crew members should monitor such clearances, one of them recording the clearance on the Master Document as it is received, the other cross-checking the receipt and read-back. All waypoint co-ordinates should be read back in detail, adhering strictly to standard ICAO phraseology, except where approved local procedures make this unnecessary. Detailed procedures pertaining to abbreviated clearances/read-backs are contained in the appropriate AIPs, and in Chapter 6, ‘Oceanic ATC Clearances’.
 

Position Plotting

It is very helpful to use a simple plotting chart to provide a visual presentation of the intended route which, otherwise, is defined only in terms of navigational co-ordinates. Plotting the intended route on such a chart may reveal errors and discrepancies in the navigational co-ordinates which can then be corrected immediately, before they reveal themselves in terms of a deviation from the ATC cleared route. As the flight progresses, plotting the aircraft's position on this chart will also serve the purpose of a navigation cross check, provided that the scale and graticule are suitable.

As the flight progresses in oceanic airspace, plotting the aircraft's position on this chart will help to confirm (when it falls precisely on track) that the flight is proceeding in accordance with its clearance. However, if the plotted position is laterally offset, the flight may be deviating unintentionally, and this possibility should be investigated at once.

It is recommended that a chart with an appropriate scale be used for plotting. Many company Progress Charts are of the wrong scale or too small. The AERAD Charts NAT 1 and NAT 2, plus AT(H)2 and AT(H)3 are all useful compromises between scale and overall chart size, while the NOAA/FAA North Atlantic Route Chart has the advantage, for plotting purposes, of a 1° latitude/longitude graticule.
 

Provision of Step-Climbs

Tactical radar control and tactical procedural control are exercised in some areas of the NAT MNPS Airspace. However, oceanic ATC clearances for most NAT flights are of a strategic nature, whereby flights are allocated a conflict-free route and profile, from coast-out to coast-in. Almost all such strategic clearances specify a single entry flight level and assume that this level will be maintained throughout the NAT portion of flight. Prior to the introduction of RVSM in the NAT MNPS Airspace there were few opportunities for subsequent step climb reclearances. With the increased number of available flight levels in RVSM airspace there is now greater scope for en-route tactical reclearances which afford the possibility of step-climbs. Controllers will accommodate requests for step-climbs whenever possible. It is important that pilots always report to ATC immediately on reaching any new cruising level.
 

Relief Crew Members

Very long range operations may include the use of relief crew. In such cases it is necessary to ensure that navigational procedures are such that the continuity of the operation is not interrupted, particularly in respect of the handling and treatment of the navigational information.
 

PRE-FLIGHT PROCEDURES

initial Insertion of Latitude and Longitude (Inertial Systems)

For inertial systems any latitude error in the initial position can introduce a systematic error which cannot be removed in flight, even by updating the present position. Correct insertion of the initial position must therefore be checked before inertial systems are aligned and the position should be recorded in the flight log and/or Master Document. Subsequent 'silent' checks of the present position should be carried out independently by both pilots during an early stage of the pre-flight checks.

With regard to the insertion of the initial co-ordinates whilst on the ramp, the following points should be taken into account:

• in some inertial systems, insertion errors exceeding about one degree of latitude will illuminate a malfunction light. It should be noted that very few systems provide protection against longitude insertion errors.

• at all times, but particularly in the vicinity of the Zero Degree E/W (Greenwich) Meridian or near to the Equator, care should be taken to ensure that the co-ordinates inserted are correct. (i.e. E/W or N/S).

Inertial Systems Alignment

The alignment of inertial systems must be completed and the equipment put into navigation mode prior to releasing the parking brake at the ramp. Some systems will align in about 10 minutes, others can take 15 minutes or more; expect alignment to take longer in extreme cold or at higher latitudes. A rapid realignment feature is sometimes provided but should only be used if, during an intermediate stop, it becomes necessary to increase the system accuracy. The aircraft must be stationary during rapid realignment which typically will take about one minute.

To ensure that there is adequate time for the initial alignment, the first crew member on the flight deck should normally put the inertial system(s) into the align mode as soon as practicable.
 

GPS Pre-departure Procedures

When both required LRNSs are GPSs their operation must be approved in accordance with FAA HBAT 95-09 or equivalent national or JAA documentation and special pre-departure procedures are required. In these cases, operators conducting GPS primary means navigation in MNPS Airspace must utilize a Fault Detection and Exclusion (FDE) Availability Prediction Programme for the installed GPS equipment; one that is capable of predicting, prior to departure for flight on a specified route*, the following:

• the maximum outage duration of the loss of fault exclusion;

• the loss of fault detection; and

• the loss of navigation function.

*Note: "specified route" is defined by a series of waypoints (to perhaps include the route to any required alternate), with the time between waypoints based on planned speeds. Since flight planned ground speeds and/or departure times may not be met, the pre-departure prediction must be performed for a range of expected ground speeds.

This FDE programme must use the same FDE algorithm that is employed by the installed GPS equipment. In order to perform the prediction accurately, the FDE prediction programme must provide the capability to manually designate satellites that are scheduled to be unavailable. Information on GPS satellite outages is promulgated via the U.S. NOTAM Office.

When GPS is being used as a supplementary navigation means or when GPS is only one of the two LRNSs required for MNPS approval (e.g. when the second LRNS is an IRS/INS installation) then some States of Registry may not require the operator to conduct pre-flight FDE checks.
 

Operational Control Restrictions
Any predicted satellite outages that affect the capability of GPS navigation may require that the flight be cancelled, delayed or re-routed.

Effects of Satellite Availability
Given suitable geometry:

• four appropriately configured satellites are required to determine position;

• five appropriately configured satellites are required to detect the presence of a single faulty satellite; and

• six appropriately configured satellites are required to identify the faulty satellite and exclude it from the navigation solution.

Note: the above number of satellites may be reduced if barometric aiding is used.

The Capability to Determine Position
Prior to departure, the operator must use the FDE prediction programme to demonstrate that there are no outages in the capability to determine position on the specified route of flight. If such outages are detected by the program, the flight must be cancelled, delayed or re-routed.

Determination of the Availability of Fault Exclusion
Once the position determination function is assured, the operator must use the FDE prediction programme to demonstrate that the maximum outage of the fault exclusion function, (i.e. 6 satellites available), for the specified route of flight, does not exceed 51 minutes in MNPS Airspace; otherwise the flight must be cancelled, delayed or re-routed.
 

Loading of Initial Waypoints

The manual entry of waypoint data into the navigation systems must be a co-ordinated operation by two persons, working in sequence and independently: one should key in and insert the data, and subsequently the other should recall it and confirm it against source information. It is not sufficient for one crew member just to observe another crew member inserting the data.

The ramp position of the aircraft, plus at least two additional waypoints, or, if the onboard equipment allows, all the waypoints relevant to the flight, should be loaded while the aircraft is at the ramp. However, it is more important initially to ensure that the first enroute waypoint is inserted accurately.

During flight, at least two current waypoints beyond the leg being navigated should be maintained in the Control Display Units (CDUs) until the destination ramp co-ordinates are loaded. Two pilots should be responsible for loading, recalling and checking the accuracy of the inserted waypoints; one loading and the other recalling and checking them independently. Where remote loading of the units is possible, this permits one pilot to cross-check that the data inserted automatically is accurate. This process should not be permitted to engage the attention of both pilots simultaneously during the flight.

An alternative and acceptable procedure is for the two pilots silently and independently to load their own initial waypoints and then cross-check them. The pilot responsible for carrying out the verification should work from the CDU display to the Master Document rather than in the opposite direction. This may lessen the risk of the pilot 'seeing what is expected to be seen’ rather than what is actually displayed.
 
 

Flight Plan Check

The purpose of this check is to ensure complete compatibility between the data in the Master Document and the calculated output from the navigation systems. Typical actions could include:

• checking the distance from the ramp position to the first waypoint. Some systems will account for the track distance involved in an ATC SID; in others, an appropriate allowance for a SID may have to be made to the great circle distance indicated in order to match that in the Master Document. If there is significant disagreement, rechecking initial position and waypoint co-ordinates may be necessary.

• selecting track waypoint 1 to waypoint 2 and doing the following:

• checking accuracy of the indicated distance against that in the Master Document;

• checking, if possible, that the track displayed is as listed in the Master Document. (This check will show up any errors made in lat/long designators (i.e. N/S or E/W).)

• similar checks should be carried out for subsequent pairs of waypoints and any discrepancies between the Master Document and displayed data checked for possible waypoint insertion errors. These checks can be co-ordinated between the two pilots checking against the information in the Master Document.

• when each leg of the flight has been checked in this manner it should be annotated on the Master Document by means of a suitable symbology as previously suggested.

• some systems have integral navigation databases and it is essential that the recency of the database being used is known. It must be recognized that even the co-ordinates of waypoint positions contained in a data base have been keyed in at some point by another human. The possibility of input errors is always present. Do not assume the infallibility of navigation databases and always maintain the same thorough principles which are applied in the checking of your own manual inputs.

Leaving the Ramp

The aircraft must not be moved prior to the navigation mode being initiated, otherwise inertial navigation systems must be realigned.

After leaving the ramp, inertial groundspeeds should be checked (a significantly erroneous reading may indicate a faulty or less reliable unit). A check should be made on any malfunction codes whilst the aircraft is stopped but after it has taxied at least part of the way to the take-off position; any significant ground-speed indications whilst stationary may indicate a faulty unit such as a tilted platform.
 

IN FLIGHT PROCEDURES

Initial flight

During the initial part of the flight, ground navaids should be used to verify the performance of the LRNSs.
 

ATC Oceanic Clearance

Where practicable, two flight crew members should listen to and record every ATC clearance and both agree that the recording is correct. Any doubt should be resolved by requesting clarification from ATC.

If the ATC oceanic cleared route is identical to the flight planned track, it should be drawn on the plotting chart and verified by the other pilot.

If the aircraft is cleared by ATC on a different track from that flight planned, it is strongly recommended that a new Master Document be prepared showing the details of the cleared track. Overwriting of the existing flight plan can cause difficulties in reading the waypoint numbers and the new co-ordinates. For this purpose, a pro-forma should be carried with the flight documents. One flight crew member should transcribe track and distance data from the appropriate reference source onto the new flight plan pro-forma and this should be checked by another crew member. If necessary, a new plotting chart may be used on which to draw the new track. The new document(s) should be used for the oceanic crossing. If the subsequent domestic portion of the flight corresponds to that contained in the original flight plan, it should be possible to revert to the original Master Document at the appropriate point.

Experience suggests that when ATC issues a reclearance involving re-routing and new waypoints, there is a consequential increase in the risk of errors being made. Therefore, this situation should be treated virtually as the start of a new flight; and the procedures employed with respect to the following, should all be identical to those procedures employed at the beginning of a flight:

• copying the ATC reclearance;

• amending the Master Document;

• loading and checking waypoints;

• extracting and verifying flight plan information, tracks and distances, etc.; and

• the preparation of a new chart;

Strict adherence to the above procedures should minimize the risk of error. However, flight deck management should be such that one pilot is designated to be responsible for flying the aircraft whilst the other pilot carries out any required amendments to documentation and reprogramming of the navigation systems - appropriately supervised by the pilot flying the aircraft, as and when necessary.
 

Approaching the Ocean

Prior to entering MNPS Airspace, the accuracy of the LRNSs should be thoroughly checked, if necessary by using independent navigation aids. For example, INS position can be checked by reference to en-route or proximate VOR/DMEs, etc.

When appropriate, the navigation system which, in the opinion of the pilot, has performed most accurately since departure should be selected for automatic navigation steering.

In view of the importance of following the correct track in oceanic airspace, it is advisable at this stage of flight that, if carried, a third pilot or equivalent crew member should check the clearance waypoints which have been inserted into the navigation system, using source information such as the track message or data link clearance if applicable.

Entering the MNPS Airspace and Reaching an Oceanic Waypoint

When passing waypoints, the following checks should be carried out:

• just prior to the waypoint, check the present position co-ordinates of each navigation system against the cleared route in the Master Document, and

• check the next two waypoints in each navigation system against the Master Document.

• at the waypoint, check the distance to the next waypoint, confirm that the aircraft turns in the correct direction and takes up a new heading and track appropriate to the leg to the next waypoint.

• before transmitting the position report to ATC, verify the waypoint co-ordinates against the Master Document and those in the steering navigation system. When feasible the position report "next" and "next plus 1" waypoint co-ordinates should be read from the CDU of the navigation system coupled to the autopilot.

Even if Automatic Waypoint Reporting (AWPR) via data link is being used to provide position reports to ATC the above checks should still be performed.

The crew should be prepared for possible ATC follow-up to the position report.
 

Routine Monitoring

It is important to remember that there are a number of ways in which the autopilot may unobtrusively become disconnected from the steering mode. Therefore, regular checks of correct engagement with the navigation system should be made.

It is recommended that where possible the navigation system coupled to the autopilot should display the present position co-ordinates throughout the flight. If these are then plotted as suggested above, they will provide confirmation that the aircraft is tracking in accordance with its ATC clearance. Distance to go information should be available on the instrument panel, whilst a waypoint alert light, where fitted, provides a reminder of the aircraft’s imminent arrival over the next waypoint.

A position check should be made at each waypoint and the present position plotted 10 minutes after passing each waypoint. For a generally east-west flight, it may be simpler to plot present position a further 2 degrees of longitude after each 10 Degree waypoint. There may be circumstances, (e.g. when, due to equipment failure, only one LRNS remains serviceable) that additional plots midway between each waypoint may be justified.

The navigation system not being used to steer the aircraft should display cross-track distance and track angle error. Both of these should be monitored, with cross-track distance being displayed on the HSI where feasible.
 

Approaching Landfall

When the aircraft is within range of land based navaids, and the crew is confident that these navaids are providing reliable navigation information, consideration should be given to updating the LRNSs. Automatic updating of the LRNSs from other navaids should be closely monitored, and before entry into airspace where different navigation requirements have been specified (e.g. RNP5 in European BRNAV airspace), crews should use all aids (including VORs and DMEs) to confirm that the in-use navigation system is operating to the required accuracy. If there is any doubt regarding system accuracy, the appropriate ATC unit should be informed.
 
 
 

SPECIAL IN FLIGHT PROCEDURES

Monitoring during Distractions from Routine

Training and drills should ensure that minor emergencies or interruptions to normal routine are not allowed to distract the crew to the extent that the navigation system is mishandled.

If during flight the autopilot is disconnected (e.g. because of turbulence), care must be taken when the navigation steering is re-engaged to ensure that the correct procedure is followed. If the system in use sets specific limits on automatic capture, the across-track indications should be monitored to ensure proper recapture of the programmed flight path/profile.

Where crews have set low angles of bank, perhaps 10° or less, say for passenger comfort considerations, it is essential to be particularly alert to possible imperceptible departures from cleared track.
 

Avoiding Confusion between Magnetic and True Track Reference

To cover all navigation requirements, some airlines produce flight plans giving both magnetic and true tracks. However, especially if crews are changing to a new system, there is a risk that at some stage (e.g. during partial system failure, reclearances, etc.), confusion may arise in selecting the correct values. Operators should therefore devise procedures which will reduce this risk, as well as ensuring that the subject is covered during training.

Crews who decide to check or update their LRNSs by reference to VORs should remember that in the Canadian Northern Domestic Airspace these may be oriented with reference to true north, rather than magnetic north.
 

Navigation in the Area of Compass Unreliability

In areas of compass unreliability basic inertial navigation requires no special procedures but most operators feel it is desirable to retain an independent heading reference in case of system failure.

Different manufacturers may offer their own solutions to the special problems existing in areas of compass unreliability. Such solutions should not however involve the use of charts and manual measurement of direction.
 

Deliberate Deviation from Track

Deliberate temporary deviations from track are sometimes necessary, usually to avoid severe weather; whenever possible, prior ATC approval should be obtained. Such deviations have often been the source of gross errors as a consequence of failing to re-engage the autopilot with the navigation system. It should also be noted that selection of the 'turbulence' mode of the autopilot on some aircraft may have the effect of disengaging it from the aircraft navigation system. After use of the turbulence mode, extra care should be taken to ensure that the desired track is recaptured by the steering navigation system.
 

POST-FLIGHT PROCEDURES

Inertial Navigation System Accuracy Check:

At the end of each flight, an evaluation of accuracy of the aircraft's navigation systems should be carried out. Equipment operating manuals specify maxima for radial errors before a system is considered to be unserviceable. For inertial systems these are in the order of 3 or 4 nm per hour. One method used to determine radial error is to input the shutdown ramp position; in other systems error messages are output giving differences between raw inertial reference positions and computed radio navigation updated positions. Whatever method is used, a record should be kept of the performance of each INS.
 

HORIZONTAL NAVIGATION PERFORMANCE MONITORING

The navigation performance of operators within NAT MNPS Airspace is monitored on a continual basis. The navigation accuracy achieved by NAT MNPS aircraft is periodically measured and additionally all identified instances of significant deviation from cleared track are subject to thorough investigation by the NAT Central Monitoring Agency (CMA), currently operated on behalf of the NAT SPG by the UK National Air Traffic Services Limited.

When a GNE is identified, follow-up action after flight is taken, both with the operator and the State of Registry of the aircraft involved, to establish the reason/cause and to confirm the approval of the flight to operate in NAT MNPS Airspace. The format of the (navigation) Error Investigation Form used for follow-up action is as shown at Attachment 1. Operational errors can have a significant effect on the assessment of risk in the system. For their safety and the safety of other users, crews are reminded of the importance of co-operating with the reporting OAC in the provision of incident information.

The overall navigation performance of all aircraft in the MNPS Airspace is continually assessed and compared to the standards established for the Region, to ensure that the TLS is being maintained.

(C) HANKE-Aviation GmbH 2014