The airspace of the North Atlantic (NAT), which links Europe and North America, is the busiest oceanic airspace in the world. In 2012 approximately 460,000 flights crossed the North Atlantic and that volume of traffic continues to increase. Direct Controller Pilot Communications (DCPC) and ATS Surveillance are unavailable in most parts of the NAT Region. Aircraft separation, and hence safety, are ensured by demanding the highest standards of horizontal and vertical navigation performance/accuracy and of operating discipline.
This article is intended to provide an overview of the NAT Region airspace including its divisions and basic operating rules.
The North Atlantic (NAT) Region
The North Atlantic Region encompasses virtually all of the non-domestic airspace over the Atlantic Ocean between roughly 20° north latitude and the North Pole except the airspace of New York Oceanic West. It is divided into a total of seven Oceanic Control Areas (OCAs) / Flight Information Regions (FIRs). These OCAs / FIRs are as follows:
- Nuuk BGGL FIR (airspace above FL195 south of 63°30" N is controlled by Gander, north of that latitude is controlled by Reykjavik and is considered part of their respective control area)
- Reykjavik OCA / BIRD FIR
- Bodø Oceanic ENOB FIR / Bodø OCA (above FL195)
- Gander OCA / CZQX FIR
- Shanwick OCA / EGGX FIR
- New York Oceanic East OCA / KZWY FIR
- Santa Maria OCA / LPPO FIR
Embedded within the North Atlantic Region are a number of domestic CTAs / TMAs including:
- Reykjavik (Iceland)
- Santa Maria (The Azores)
Over the high seas, the lower limit of all NAT oceanic control areas is FL55. There is no upper limit. Airspace at and above FL55 is Class A controlled airspace and below FL55 it is Class G uncontrolled airspace.
All flights operating at or above FL60 must be conducted in accordance with Instrument Flight Rules (IFR), even when not operating in instrument meteorological conditions (IMC). Clearance for Visual Flight Rules (VFR) climb or descent - a climb or descent while maintaining own separation while in Visual Meteorological Conditions (VMC) - will not be issued.
Strategic Lateral Offset Procedures (SLOP) are authorized and encouraged.
Separation within NAT airspace is procedural and is based on altitude, distance and time.
Vertical separation of 1000' is provided between FL60 and FL280 as well as in the Reduced Vertical Separation Minimum airspace. Flights above FL410 will be separated by 2000' vertically.
Lateral separation is distance based and is approximately one degree of latitude (60 nm). Performance Based Communications and Surveillance (PBCS) tracks (formerly Reduced Lateral Separation Minimum (RLatSM) tracks) allow suitably equipped, certified and authorised aircraft to fly tracks separated by half of one degree.
Longitudinal separation between subsequent aircraft following the same track (in-trail) and between aircraft on intersecting tracks is time-based and is thus expressed in clock minutes. The standard time interval between aircraft following the same route with the same assigned speed is 10 minutes. That time interval wil be adjusted to accommodate aircraft with different speed assignments, shorter if the leading aircraft is faster and longer if the leading aircraft is slower. Aircraft separation is assessed in terms of differences between the respectie ATAs / ETAs at common points. The maintenance of in-trail separations is aided by the application of the Mach Number Technique in which jet aircraft are assigned a specific mach number as part of their clearance. However, aircraft clock errors resulting in waypoint ATA and ETA errors in position reports can lead to an erosion of actual longitudinal separations between aircraft. It is thus vitally important that the time-keeping device intended to be used to indicate waypoint passing times is accurate, and is synchronised to an acceptable UTC time signal before commencing flight in NAT airspace.
Operation of Transponders
Transponders should be operated at all times while in North Atlantic (NAT) region and set to squawk Code 2000. However, the last ATC assigned code must be retained for a period of 30 minutes after entry into NAT airspace unless otherwise directed by ATC. One exception to this requirement should be noted. Because of the limited time spent in the NAT HLA airspace when flying on Routes Tango 9 or Tango 290 (across the Bay of Biscay just west of the BOTA boundary), the change from the last assigned domestic code to Code 2000 should be made northbound 10 minutes after passing BEGAS or ADVAT and southbound 10 minutes after passing LASNO or GELPO.
These procedures in no way affect the use of the special purpose codes 7500, 7600 and 7700.
As Reykjavik ACC provides radar control service in the south-eastern part of its area, transponder codes issued by that facility must be retained throughout that area until advised by ATC.
High Level Airspace (HLA)
A large portion of the airspace of the North Atlantic Region, between FLs 285 and 420 inclusive, is designated as the NAT High Level Airspace (NAT HLA). Until February 2016, most of this airspace was designated Minimum Navigation Performance Standards (MNPS) airspace. The re-designation from MNPS to HLA is in keeping with the transition from capability based (MNPS) to Performance Based Navigation (PBN) in this segment of the NAT airspace. The lateral dimensions of the HLA include Gander, Reykjavik, Bodø Oceanic, Shanwick (except the Shannon Oceanic Transition Area (SOTA) and Brest Oceanic Transition Area (BOTA)), Santa Maria Oceanic and that portion of New York Oceanic East that is north of 27° N. Within this airspace a formal Approval Process by the State of Registry of the aircraft or the State of the Operator ensures that aircraft meet defined NAT HLA Standards and that appropriate crew procedures and training have been adopted. HLA Standards include the requirement for two approved independent Long Range Navigation Systems (LRNS). It should be noted that State Approvals for NAT MNPS operations granted prior to 04 February 2016 will be valid for NAT HLA operations with the exception that those Approvals issued prior to 01 January 2015 and based upon the earlier “6.3 NMs” MNPS standard, are not valid after January 2020.
The unique, unidirectional, flexible track structure of the North Atlantic Organised Track System (NAT OTS) is located within HLA, predominantly in the Gander and Shanwick Oceanic CTAs.
Provisions for Aircraft Not Meeting HLA / MNPS Criteria
Aircraft not meeting the navigation requirements for HLA airspace can choose to fly above FL420 or below FL285. Additionally, within the HLA, special routes, referred to as "Blue Spruce Routes", have been designated for aircraft equipped with only one LRNS plus normal short-range navigation equipment (VOR, DME, ADF), which require to cross the North Atlantic between Europe and North America (or vice versa). As these routes are within NAT HLA Airspace, State approval must be obtained prior to flying along them. These routes are also available for interim use by aircraft normally approved for unrestricted NAT HLA operations that have suffered a partial loss of navigation capability and have only a single remaining functional LRNS.
Reduced Vertical Separation Minimum (RVSM) Airspace
Reduced Vertical Separation Minima (RVSM), in the band of altitudes FL290 - FL410, is applicable in all NAT HLA. Aircraft not RVSM certified will be cleared either above or below RVSM airspace. These aircraft may be cleared to climb or descend through RVSM airspace on a non-interference basis.
ATC may provide special approval for a NAT HLA MNPS approved aircraft that is not approved for RVSM operation to fly in NAT HLA airspace provided that the aircraft:
- is on a delivery flight; or
- was RVSM approved but has suffered an equipment failure and is being returned to its base for repair and/or re-approval; or
- is on a mercy or humanitarian flight.
Prior coordination is required.
Data Link Mandated Airspace
The first phase of the mandate for data link services in the North Atlantic (NAT) region commenced 7 February 2013. As of that date, all aircraft operating on or at any point along two specified tracks within the NAT OTS between FL 360 to FL 390 (inclusive) during the OTS validity period were required to be fitted with, and using, Controller Pilot Data Link Communications (CPDLC) and Automatic Dependent Surveillance - Contract (ADS-C).
Phase 2A of the ICAO NAT Region Data Link Mandate was implemented on 05 February 2015. In this phase the CPDLC / ADS-C mandated airspace includes all OTS tracks at FL 350 to FL 390, inclusive. To flight plan or fly in the altitude band FL 350-390 inclusive on any OTS track, aircraft must be equipped with and operating FANS 1/A or equivalent CPDLC and ADS-C.
Phase 2B, commencing 7 December 2017, expanded CPCLC / ADS-C mandated airspace to include FL 350 to FL 390 (inclusive) throughout the ICAO NAT region.
Phase 2C, commencing 30 January 2020, further expands CPCLC / ADS-C mandated airspace to include FL 290 and above throughout the ICAO NAT region.
Currently, the mandate incorporates FL290 to FL410 inclusive, except:
- Airspace north of 80° North;
- New York Oceanic East flight information region (FIR);
- Airspace where
- ATS surveillance service is provided, and
- VHF voice communications provided, and
- the aircraft is suitably equipped (transponder/ADS-B extended squitter transmitter)
Certain categories of flights (e.g. SAR, MEDEVAC, STATE, etc.) may be allowed to plan and operate through the mandated airspace with non-equipped aircraft.
Aircraft not equipped with FANS 1/A (or equivalent) may request to climb or descend through the NAT DLM airspace. Such requests are to be considered on a tactical basis.
With full implementation of Data Link Mandated Airspace, there will be a corridor, in the same geographic area as the current Blue Spruce Routes, for aircraft not equipped with CPDLC / ADS-C. Aircraft using this corridor will, however, require Automatic Dependent Surveillance - Broadcast (ADS-B) equipment.