In geographical areas where air traffic control can track aircraft with limited coverage, Minimum Navigation Performance Specification has been designed .
This requires aircraft to operate with enhanced tracking capabilities and redundant navigational means.
These requirements enable to diminish separations between aircraft to maintain an air traffic flow well above operational limitations otherwise.
The area of reference for this article is the North Atlantic Region - High Level Airspace (NAT HLA).
If local provisions exist, they can be found in national AIPs.
Flights shall be conducted in accordance with the Instrument Flight Rules when operated at or above flight level (FL) 60 or 600 m (2 000 ft) above ground, whichever is the higher.
The following items must be stated in the flightplan of any aircraft operating through the NAT region:
- REG/ in field 18 if the aircraft registration is not the aircraft callsign
- CODE/ in field 18 stating the aircraft address if available
- Mach number at any portion of oceanic transit should be inserted in field 15.
Any requirements regarding the route formatting can be found in the subchapter navigation
In addition to the previous prerequisites, the following table will summarize the required serviceable items to be present in the flightplan of any aircraft operating through the NAT HLA:
- Navigation equipment
- Communication equipment
- Surveillance equipment
|Item||Case 10a designator||Case 18 designator|
|RNP 10 or/and RNP 4 capabilities||R||PBN/A1 or/and PBN/L1|
|CPDLC capability||J2 or J5 or J7||CODE/|
|Item||Case 10a designator||Case 18 designator|
|ADS-B||B1 or B2||Nil|
Note that the required PBN differs depending on the FIR in which the aircraft operates. Refer to navigation chapter for conditions of applicability.
Estimated Elapsed Time (EET/) should not be inserted on the IVAO network due to software limitations. The risk is to generate a too large flightplan which will not be visible by the ATCs.
An aircraft which is not meeting MNPS requirements shall not be allowed to operate in NAT HLA unless:
- ATS surveillance service is being provided
- Direct controller-pilot VHF voice communication is maintained
- Equipment to maintain navigation accuracy is serviceable and used to navigate along the cleared track.
The Minimum Equipment List (MEL) of the aircraft may include possible deviations with or without operating restrictions depending on failed system's redundancy.
We assume in the following table that the applicability automatically includes holding a valid MNPS certification.
If no additional requirements are mentioned, then it is applicable to any aircraft simply holding a MNPS certificate.
|Applicable FIR||Minimum distance between 2 aircraft||Applicability/Restrictions|
|23 NM||RNP 4
|30 NM||RNP 4
|50 NM||RNP 10
|All||60 NM||Both traffic MNPS|
|All||90 NM||One traffic not MNPS|
|All||120 NM||Both traffic not MNPS|
|Applicable FIR||Minimum separation||Type of aircraft||Separation technique||Applicability/Restrictions|
RNP 10 or RNP 4
|All||10 minutes||Turbo-jet||Mach number
Common reporting point
|All||30 minutes||Non turbo-jet||Nil||Nil|
As the NAT HLA region is RVSM, between FL290 and FL410 inclusive, 1 000 ft of vertical separation should be provided between two aircraft.
For supersonic aircraft only: when operating at or above FL450, at least 4 000 ft should exist between a supersonic aircraft and any other traffic.
This part does not deal with phraseology but solely with regulatory aspects in relation to communication means and requirements.
See phraseology accordingly.
Before entering the NAT control areas, flight crews are required to request their oceanic clearance.
The contents of this message must include:
- The track code if navigating by use of the Organised Track System; or, the full routing that the aircraft must follow using waypoint identifiers and geographical coordinates as appropriate
- The cleared flight level
- The cleared Mach number
- the part "SEND MET REPORTS" if in-flight meteorological information is sought by ATS.
The flight crew is required to read-back the clearance in its entirety, including the full routing as applicable.
Depending on the sector, flight crews are required to retrieve their oceanic clearance at least a minimum of time before effective entry.
Due to air traffic flow management, traffic may be assigned a time of entry into NAT airspace. This time will be indicated in the clearance using the 4-digit format.
When operating inside the NAT airspace, flight crews are required to transmit their position by means of position reports. These reports must take place at the following locations:
- For east-west direction:
- Any intermediate meridians between 5°W and 65°W at intervals of 10 degrees of longitude south of 70°N
- Any intermediate meridians between 10°W and 50°W at intervals of 20 degrees of longitude north of 70°N
- For south-north direction: as applicable by the cleared route.
- Whenever the aircraft reaches a significant waypoint as applicable on an organised track.
The contents of these messages must include:
- The current position in latitude and longitude or using the waypoint
- The current time, or if posterior, the time at which the point of report was overflown
- The current flight level
- The current Mach number
- The next waypoint to be flown
- The estimated time at which the next waypoint will be overflown
- The waypoint to be overflown thereafter
- In-flight meteorological information only if sought explicitly by ATS in the clearance.
The flight crew should expect a full read-back of the report by the ATC.
Contrary to the general phraseology rule indicating to express time by solely using minute reference, time in position reports should be indicated using the 4-digit format.
If the expected time of arrival overhead the next waypoint is found to be in error of 3 minutes or more, a revised estimate should be given to the ATS unit as soon as possible.
When fitted with the appropriate equipment, flight crews should endeavor to maximise use of CPDLC while flying through the NAT region.
This can be achieved on the IVAO network by using the text interface of the IVAO Pilot interface.
SELCAL watch fulfills the requirement to maintain an active air-ground communication watch.
However, when serviceable and aimed to be used, it requires:
- the inclusion of the SELCAL code in the flightplan in field 18 using identifier SEL/
- an operational check of the SELCAL equipment prior to or at the entry point
Air traffic controllers can review the use of the SELCAL with consulting the adequate documentation corresponding to his IVAO ATC software.
Not applicable on the IVAO network.
Prior to operating in the NAT FIRs between FL285 and FL420, at least one of the following Performance-Based Navigation items should be achieved for MNPS certification:
- RNAV 10
- RNP 4
When necessary in order to optimise the flow of air traffic inside the FIRs of CZQX, EGGX, KZWY, LPPO and BIRD, an organised track system (OTS) can be established.
The OTS consists of establishing routes for the day allowing the flow of traffic to be divided onto different tracks, enabling the use of separation between traffic more accurately and more precisely.
Flight crews should plan to file a route using the OTS when possible.
In that case, the flightplan should mention the track to be used in the route (field 15) using the following format: NATx; where x is the track identifier according to the OTS message.
It is a requirement to carry a copy of the OTS message to allow for a crosscheck of routing if deemed necessary.
The OTS message can be found here: official OTS message
Depending on the traffic levels on each track, an aircraft can be re-routed and assigned a new track by the ATC when copying its oceanic clearance.
Subsequently, it is vital to perform the new route insertion, crosscheck the FMC route against the OTS message, and clarify any doubts about the routing if necessary.
When planning the route, if it becomes necessary that the use of organised track system is not suitable, then it is possible to plan a route across the NAT region using waypoints formed by the intersection of parallels and meridians, often referred to as random routing.
The following rules must be applied when planning the route:
- The elapsed time between two waypoints must not be less than 30 minutes and must not be more than 60 minutes.
A deviation to this rule is applicable to polar flights only when it is required to smooth turns onto next significant waypoints. In that case, intermediate waypoints may be used without being referenced in the flight plan route.
- For east-west direction (considered as default for Europe-North America flights), significant waypoints are formed by:
- South of 70°N inclusive: intersection of half or whole degrees of latitude with meridians spaced at intervals of 10 degrees from the Greenwich meridian to longitude 70°W
- North of 70°N and at or south of 80°N: the intersection of parallels of latitude expressed in degrees and minutes with meridians normally spaced at intervals of 20 degrees from the Greenwich meridian to longitude 60°W, using the longitudes 000W, 020W, 040W and 060W
- North of 80°N: the intersection of parallels of latitude expressed in degrees and minutes with meridians expressed in whole degrees
- For south-north direction (considered as default for any polar flights), significant waypoints are formed by:
- South of 80°N inclusive: the intersection of whole degrees of longitude with parallels of specified latitude spaced at intervals of 5°.
- North of 80°N: the intersection of parallels of latitude expressed in degrees and minutes with meridians expressed in whole degrees.
- For flights operating south of 80°N in an east-west direction, if the flight time between two significant waypoints as defined exceeds 1 hour, intermediate waypoints should be established:
- South of 70°N inclusive: at intervals of 10 degrees of longitude (between 5°W and 65°W)
- North of 70°N and south of 80°N inclusive: at intervals of 20 degrees of longitude (between 10°W and 50°W)
- Anytime the flight time between a significant point and an intermediate waypoint defined as above becomes less than 30 minutes, the intermediate waypoint can be ignored.
In a non-radar environment, deviation from the intended flightpath is a serious threat to flight safety.
This is why flight crews should regularly ensure that the aircraft's position is still within the regulatory margins defined by their PBN capabilities, following the assigned routing.
In case of deviation, the flight crew shall take all appropriate measures to fly back onto the cleared routing within a 100 NM from the position where the deviation was discovered.
In case of emergency descent, whether it be resulting in turning back or continuing further toward the end of the NAT region, it is expected from the flight crew to fly initially to a waypoint conveniently located between two OTS tracks as applicable.
As soon as possible, communications with the responsible ATS unit should be established. If no contact is established when reaching the waypoint, the aircraft must follow a parallel track located midway from two OTS tracks as applicable.
There are many possible ways of losing communications (partial or total, transmit and/or receive...) and they cannot be all described. The following part will focus on NAT-specific loss of communications.
Whenever a loss of communication is recognised, the flight crew will attempt as a general rule to establish communications with another aircraft (on GUARD frequency 121.5 for example) or with another ATS unit. If it fails, the flight crew will make sure to try again with different equipment: headset, hand microphone, VHF 2...
If this general procedure fails, the following must be followed:
- Prior to entering NAT region:
- If the oceanic clearance has been received: the flight crew will comply with the oceanic clearance. Any change of speed or flight level to comply must be done as close as possible to the oceanic entry point.
- If the oceanic clearance has not been received: the flight crew will comply with the filed flight plan at least until reaching the oceanic exit point.
- Prior to exiting NAT region:
- Oceanic clearance matches filed flight plan: the flight crew will comply with the last acknowledged instructions regarding route, flight level and speed parameters. At the exit point, the aircraft shall continue onto the filed flight plan route
- Oceanic clearance differs from filed flight plan: the flight crew will comply with the last acknowledged instructions regarding route, flight level and speed parameters. At the exit point, the aircraft shall rejoin as fast as possible the filed flight plan route by using the regional ATS route network.
When initiating a diversion, the flight crew should observe the following practice to reduce the threat of a loss of separation:
- If able, climb above FL410 or descend below FL280, then initiate the diversion while communicating with the ATC toward a conveniently located waypoint.
- If unable to comply with the previous altitude constraints, a 45-degree turn must be initiated to rejoin a 15-NM track offset at which the aircraft will climb or descend by intervals of 500ft. If unable to contact the ATS unit, a turn toward a conveniently located waypoint should be initiated.
We encourage you to read the documentation article dealing with oceanic phraseology.