ATS Route Designators and Their Regulatory Significance for International Operators

ICAO Annex 11 defines ATS route designators as a single letter followed by a number (1–999) that uniquely identifies published airways. The letter indicates the route type and network membership: for example, A, B, G, and R designate regional ATS routes based on conventional ground-based navigation aids, while L, M, N, and P designate regional RNAV (Area Navigation) routes. In practice, A‑routes and R‑routes are conventional airways using VHF Omnidirectional Range (VOR), Distance Measuring Equipment (DME), or Non-Directional Beacon (NDB) navigation, forming part of the global airway network, whereas L‑routes and M‑routes are published RNAV airways, typically GPS-based, within the network.

 

Supplementary prefixes may be applied, such as U for upper-air routes or K for helicopter routes, and suffix letters (e.g., F or G) can indicate advisory-only segments. All ATS route designators are standardized by ICAO and published in national Aeronautical Information Publications (AIPs), making them mandatory for IFR flight planning and ATC clearances.

R, A vs. L, M: Conventional vs. RNAV Routes

According to ICAO conventions, A- and R‑routes are regional conventional routes based on ground-based navigation aids, while L- and M‑routes are regional RNAV routes. L- and M‑routes require RNAV-equipped aircraft, typically using GPS/WAAS or an FMS, and a specified RNP level. In contrast, A- and R‑routes can be flown using conventional navigation aids such as VOR and DME. For example, Canada’s Aeronautical Information Manual (AIM) defines L‑routes as fixed low-level RNAV routes that require GNSS-equipped RNAV systems.

 

Similarly, the New Zealand Aeronautical Information Publication (AIP) specifies that RNAV routes identified by the letters L, M, N, or P are for aircraft equipped with an Inertial Navigation System (INS), Flight Management System (FMS), or Global Navigation Satellite System (GNSS) meeting RNP‑10 (RNAV‑10) performance or better. Conventional A- and R‑routes do not have RNAV requirements and connect traditional fixes or navaids within the regional airway network.

 

• Key Point: L and M route prefixes indicate published GPS/FMS-based airways (RNAV), whereas A and R indicate published conventional VOR/DME airways. A business jet must have the required RNAV certification/equipment to use L/M routes (for example, RNP5 or RNP10), but could fly A/R routes with standard VOR/DME navigation.

RNAV Equipment and Performance Requirements

Operators flying L- and M‑routes must meet the specified RNP level for those RNAV routes. For example, the New Zealand Auckland Oceanic AIP requires RNP‑10 or better for oceanic RNAV routes, while Kazakhstan’s AIP specifies RNAV‑5 (5 NM accuracy) for its L‑ and M‑routes. ICAO also mandates RNP‑10 (RNAV‑10) or RNP‑4 for flights within structured oceanic airspace.

 

In practice, this requires business jets to be equipped with GNSS, INS, or FMS systems capable of meeting the applicable RNP specification for any RNAV (L or M) route. For instance, a Gulfstream G650 with RNP‑10 approval can operate legally on North Atlantic L- or M‑routes, whereas a non‑GNSS-equipped light jet cannot. Conventional A- or R‑routes do not impose RNAV requirements beyond standard instrument navigation capabilities.

 

• Example (Equipment): A Canadian ATC advisory notes “L‑routes require GNSS RNAV systems”, implying any aircraft must be GPS‑certified to file those routes.
• Regulatory Implication: If an aircraft lacking RNAV capability files an L/M‑route, the flight plan is invalid under ICAO rules. Operators must file a feasible route or request a direct RNAV clearance only if qualified.

Structured Airspace Regions (Oceanic and High-Level)

In major oceanic and high-level regions, such as the North Atlantic and Pacific, ATS routes are highly structured and frequently restricted to RNAV-equipped aircraft. The North Atlantic Tracks (NAT) between Europe and North America provide a prime example: above FL290, aircraft must meet Automatic Dependent Surveillance–Contract (ADS‑C), Controller–Pilot Data Link Communications (CPDLC), and RNP‑10 (RNAV‑10) minimum performance standards.

 

ICAO’s NAT Operations Manual explicitly mandates RNP‑10 (or RNP‑4 where applicable) for high-level NAT airspace. Therefore, business jets operating at these altitudes are legally required to have RNP‑10 capability and the necessary data link systems, independent of route designators.

 

Within NAT airspace, daily published tracks are assigned designators such as Track A, Track B, or Track C, and flight plans use prefixes (e.g., “NATA,” “NATB”) to reflect these tracks. Similarly, Asia-Pacific structured RNAV routes frequently employ RNP‑10 standards and are designated with L or R prefixes for high-level route planning.

 

• Example (Transoceanic Flight): A business jet flight from London (Luton) to New York must file a NAT track or random RNAV route. This clearance is legal only if the aircraft is RNP10-approved and CPDLC/ADS‑C The chosen track’s designator (e.g. NATF) and waypoints appear on the IFR flight plan, reflecting ICAO’s Annex 2 and Annex 11 requirements.
• Oceanic Random Routes: Outside organized track periods, pilots may file “random” RNAV routes (great‑circle routing) in the NAT, but still at RNAV standards. If the flight enters the NAT HLA, it automatically falls under NAT procedure (RNP10, ADS‑C) as above.

Flight Planning and Legal Significance

Under ICAO regulations, ATC clearances and flight plans must reference valid ATS route designators. In practice, the filed Route field lists the sequence of route designators and waypoints (or direct segments, DCT) for each FIR. Conventional A- and R‑routes appear in enroute airspace publications, while L- and M‑routes are depicted as RNAV routes on RNAV-enroute charts.

 

Because ICAO Annex 11 and national AIPs constitute Standards or national regulations, these route designators carry legal authority: operators cannot arbitrarily create or deviate from published routes without ATC clearance. For example, operating a published A-route requires adherence to VOR/DME fixes; inserting an RNAV-only segment on an aircraft not approved for RNAV is prohibited.

 

• Plan Filing: Business jet dispatchers must use correct route designators in Item 15 of the ICAO flight plan. For flights along established ATS routes, the first route designator (e.g., “L450” or “R660”) is entered directly in the route string. If the origin or destination is not on the designated route, “DCT” is used to connect to the nearest fix or route junction.

 

• Performance Codes: When filing RNAV routes, operators should include PBN approvals in Item 18 (e.g., PBN/A1 for RNP10, PBN/L1 for RNP4) to satisfy ATC requirements. This is mandated by ICAO PANS-ATM (Doc 4444) to ensure that aircraft equipment and performance meet regulatory standards.

 

• Compliance: Failure to meet route requirements may constitute a regulatory violation. For instance, operating in North Atlantic High Level Airspace (NAT HLA) without RNP10 and ADS-C capability is not permitted under ICAO Annex 6 and relevant national regulations. Similarly, flying an RNAV (L/M) route without compliant GNSS equipment may breach the applicable AIP provisions of the State concerned.

 

Comparative Summary of Route Types

Designator	ATS Network Category	Navigation Type	Equip/Performance	Typical Use
A-route (A###)	Regional conventional (ground‑nav)	VOR/DME/NDB	No RNAV required (conventional instrument)	Published airway (e.g. high-altitude jet route in some regions)
R-route (R###)	Regional conventional (ground‑nav)	VOR/DME/NDB	No RNAV required	Similar to A‑route (some regions use “R” series for conventional routes)
L-route (L###)	Regional RNAV (GPS) route	Area Navigation (RNAV)	GNSS/FMS; e.g. RNP5 or RNP10 required	Published fixed RNAV airway (often low-to-mid altitudes or oceanic)
M-route (M###)	Regional RNAV (GPS) route	Area Navigation (RNAV)	GNSS/FMS; e.g. RNP5 required	Published RNAV airway (often high-altitude oceanic/continental)

Operational Example: Transatlantic Flight

Consider a business jet filing an IFR flight from London (EGLL) to New York (KJFK) via the North Atlantic. At FL350, the aircraft will follow the North Atlantic Track System published for that day. The flight plan would indicate the relevant track, such as North Atlantic Tracks Region (NATR) or North Atlantic Track B (NATB). Because these are structured RNAV tracks within NAT High-Level Airspace, the aircraft must be approved for RNP‑10 and equipped with ADS‑C/CPDLC. If the jet lacked RNP‑10 capability, the dispatcher would need to file an altitude below FL290 or select a non-NAT route, which may be less efficient or unavailable.

 

In contrast, a European-to-Middle East flight, for example from Paris to Dubai, may combine conventional A/R routes and RNAV L/M routes depending on the FIR. For instance, a jet might fly an A-route over Europe using ground-based navigation and transition to L/M RNAV routes over the Middle East, requiring GNSS-equipped systems for those segments. ATC clearances are valid only when the aircraft equipment and crew meet the requirements for each route segment.

 

Accurate, regulation-aligned guidance is essential for business jet operators navigating complex international airspace. Just Aviation provides expert support in interpreting ATS route designators, using user preferred routes (UPRs) strategically in oceanic and remote airspace, enabling operators to plan and execute flights with precision while maintaining compliance, efficiency, and operational confidence.