Oceanic Loss of Long Range Navigation

7.2.1 An aeroplane shall be provided with navigation equipment which will enable it to proceed:

a) in accordance with its operational flight plan; and

b) in accordance with the requirements of air traffic services; except when, if not so precluded by the appropriate authority, navigation for flights under VFR is accomplished by visual reference to landmarks.

7.2.2 For operations where a navigation specification for performance-based navigation (PBN) has been prescribed, an aeroplane shall, in addition to the requirements specified in 7.2.1:

a) be provided with navigation equipment which will enable it to operate in accordance with the prescribed navigation specification(s);

b) have information relevant to the aeroplane navigation specification capabilities listed in the flight manual or other aeroplane documentation approved by the State of the Design or State of Registry; and

c) have information relevant to the aeroplane navigation specification capabilities included in the MEL.

Note.— Guidance on aeroplane documentation is contained in the Performance-based Navigation (PBN) Manual (Doc 9613).

7.2.3 The State of the Operator shall, for operations where a navigation specification for PBN has been prescribed, ensure that the operator has established and documented:

a) normal and abnormal procedures including contingency procedures;

b) flight crew qualification and proficiency requirements in accordance with the appropriate navigation specifications;

c) a training programme for relevant personnel consistent with the intended operations; and

d) appropriate maintenance procedures to ensure continued airworthiness in accordance with the appropriate navigation specifications.

Note 1.— Guidance on safety risks and mitigations for PBN operations, in accordance with Annex 19, are contained in the Performance-based Navigation (PBN) Operational Approval Manual (Doc 9997).

Note 2.— Electronic navigation data management is an integral part of normal and abnormal procedures.

7.2.4 The State of the Operator shall issue a specific approval for operations based on PBN authorization required (AR) navigation specifications.

Note.— Guidance on specific approvals for PBN authorization required (AR) navigation specifications is contained in the Performance-based Navigation (PBN) Operational Approval Manual (Doc 9997).

7.2.5 For flights in defined portions of airspace where, based on Regional Air Navigation Agreement, minimum navigation performance specifications (MNPS) are prescribed, an aeroplane shall be provided with navigation equipment which:

a) continuously provides indications to the flight crew of adherence to or departure from track to the required degree of accuracy at any point along that track; and

b) has been authorized by the State of the Operator for the MNPS operations concerned.

Note.— The prescribed minimum navigation performance specifications and the procedures governing their application are published in the Regional Supplementary Procedures (Doc 7030).

Source: ICAO Annex 6, Volume I, §7.2

For unrestricted operation in the NAT HLA an approved aircraft must be equipped with a minimum of two fully serviceable LRNSs. Aircraft may be approved for NAT HLA operations when equipped with only a single LRNS. However, such aircraft are only permitted to plan and fly routes specified for this purpose (see paragraph 12.2) and on other particular routings serving individual traffic axes e.g. the Tango routes, routings between the Iberian Peninsula and the Azores/Madeira and routes between Iceland and Greenland (See Chapter 3).

Source: ICAO NAT Doc 007, ¶12.1.2

If abnormal navigation indications relating to INS or IRS systems occur after take-off, they should be analysed to discover their cause. Under no circumstances should a flight continue into oceanic airspace with unresolved navigation system errors, or with errors caused by inertial platform misalignment or initial position insertion.

Source: ICAO NAT Doc 007, ¶12.1.3

With only two systems on board, identifying the defective unit can be difficult. If such a situation does arise in oceanic airspace any or all of the following actions should be considered:

1. checking malfunction codes for indication of unserviceability
2. obtaining a fix. It may be possible to use the following:
1. the weather radar (range marks and relative bearing lines) to determine the position relative to an identifiable landmark such as an island; or
2. the ADF to obtain bearings from a suitable long-range NDB, in which case magnetic variation at the position of the aircraft should be used to convert the RMI bearings to true; or
3. if within range, a VOR, in which case the magnetic variation at the VOR location should be used to convert the radial to a true bearing (except when flying in the Canadian Northern Domestic Airspace where VOR bearings may be oriented with reference to true as opposed to magnetic north).
3. contacting a nearby aircraft on VHF, and comparing information on spot wind, or ground speed and drift.
4. if such assistance is not available, and as a last resort, the flight plan wind speed and direction for the current DR position of the aircraft, can be compared with that from navigation system outputs.

Source: ICAO NAT Doc 007, ¶12.1.6

Occasions may still arise when distance or cross track differences develop between systems, but the flight crew cannot determine which system is at fault. The majority of operators feel that the procedure most likely to limit gross tracking errors under such circumstances is to fly the aircraft half way between the cross track differences as long as the uncertainty exists.

Source: ICAO NAT Doc 007, ¶12.1.7

Operations or navigation manuals should include guidelines on how to decide when a navigation system should be considered to have failed, e.g. failures may be indicated by a red warning light, or by self -diagnosis indications, or by an error over a known position exceeding the value agreed between an operator and its certifying authority.

Source: ICAO NAT Doc 007, ¶12.1.8

Some aircraft carry triplex equipment (3 LRNSs) and hence if one system fails, even before take-off, the two basic requirements for NAT HLA operations may still be met and the flight can proceed normally. The following guidance is offered for aircraft having state approval for unrestricted operations in the NAT HLA and which are equipped with only two operational LRNSs:

Source: ICAO NAT Doc 007, ¶12.2.1

The flight crew must consider:

• delaying departure until repair is possible;
• obtaining a clearance above or below MNPS Airspace;
• planning on the special routes known as the ‘Blue Spruce’ Routes, which have been established for use by aircraft suffering partial loss of navigation capability (Note: As indicated in Chapter 1, these routes may also be flown by aircraft approved for NAT MNPSA operations but equipped with only a single LRNS).

Source: ICAO NAT Doc 007, ¶12.2.2

The flight crew must consider:

• landing at a suitable aerodrome before the boundary or returning to the aerodrome of departure;
• diverting via one of the special routes described previously;
• obtaining a re-clearance above or below the NAT HLA.

Source: ICAO NAT Doc 007, ¶12.2.4

Once the aircraft has entered oceanic airspace, the flight crew should normally continue to operate the aircraft in accordance with the oceanic clearance already received, appreciating that the reliability of the total navigation system has been significantly reduced.

Source: ICAO NAT Doc 007, ¶12.2.5

Once the aircraft has entered oceanic airspace, the flight crew should normally continue to operate the aircraft in accordance with the oceanic clearance already received, appreciating that the reliability of the total navigation system has been significantly reduced.

Source: ICAO NAT Doc 007, ¶12.2.5

The flight crew should however,

• assess the prevailing circumstances (e.g. performance of the remaining system, remaining portion of the flight in the NAT HLA, etc.);
• prepare a proposal to ATC with respect to the prevailing circumstances (e.g. request clearance above or below the NAT HLA, turn-back, obtain clearance to fly along one of the special routes, etc.);
• advise and consult with ATC as to the most suitable action;
• obtain appropriate re-clearance prior to any deviation from the last acknowledged oceanic clearance.

Source: ICAO NAT Doc 007, ¶12.2.6

When the flight continues in accordance with its original clearance (especially if the distance ahead within the NAT HLA is significant), the flight crew should begin a careful monitoring programme:

• to take special care in the operation of the remaining system bearing in mind that routine methods of error checking are no longer available;
• to check the main and standby compass systems frequently against the information which is still available;
• to check the performance record of the remaining equipment and if doubt arises regarding its performance and/or reliability, the following procedures should be considered:
• attempting visual sighting of other aircraft or their contrails, which may provide a track indication;
• calling the appropriate OACC for information on other aircraft adjacent to the aircraft’s estimated position and/or calling on VHF to establish contact with such aircraft (preferably same track/level) to obtain from them information which could be useful. (e.g. drift, groundspeed, wind details).

Source: ICAO NAT Doc 007, ¶12.2.7

The flight crew should:

1. immediately notify ATC;
2. make best use of procedures specified above relating to attempting visual sightings and establishing contact on VHF with adjacent aircraft for useful information;
3. keep a special look-out for possible conflicting aircraft, and make maximum use of exterior lights;
4. if no instructions are received from ATC within a reasonable period consider climbing or descending 500 feet, broadcasting action on 121.5 MHz and advising ATC as soon as possible.

Note: This procedure also applies when a single remaining system gives an indication of degradation of performance, or neither system fails completely but the system indications diverge widely and the defective system cannot be determined.

Source: ICAO NAT Doc 007, ¶12.2.8

A characteristic of the navigation computer system is that the computer element might fail, and thus deprive the aircraft of steering guidance and the indication of position relative to cleared track, but the basic outputs of the IRS (LAT/LONG, Drift and Groundspeed) are left unimpaired. A typical drill to minimise the effects of a total navigation computer system failure is suggested below. It requires comprehensive use of the plotting chart.

1. use the basic IRS/GPS outputs to adjust heading to maintain mean track and to calculate ETAs.
2. draw the cleared route on a chart and extract mean true tracks between waypoints.
3. at intervals of not more than 15 minutes plot position (LAT/LONG) on the chart and adjust heading to regain track.

Source: ICAO NAT Doc 007, ¶12.2.9