Airspace Structure

Some parts of airspace serve different purposes bases on their limits and proximity to an airfield and other important features on the ground. This page goes over the typical airspaces that one might encounter while flying or controlling in Latvia as well as Europe in general.

ATS Airspace Classification and Structure in EVRR FIR

Controlled Airspace

Control Traffic Zone (CTR)

Control Traffic Zones (CTRs) are a type of airspace that is used around controlled aerodromes. Typically such an airspace extends from the ground (SFC) to a rather low vertical limit (e.g. Riga CTR has vertical limits of SFC-2500FT). The lateral limits of a CTR are also not very large: a typical CTR extends approximately 10-15 NM around a given aerodrome. This airspace is staffed by an ATCO with an endorsement to control the Tower (position). A CTR is the first airspace that a departing aircraft crosses once airborne, and the last airspace that an arriving aircraft goes through before touchdown. Such airspaces may be either fully controlled or procedural.

EVRR FIR has 2 CTRs: Riga CTR and Lielvarde CTR. Precise dimensions and additional information on the structure and characteristics of those airspaces is available in the AIP of the Republic of Latvia.

Riga CTR

Riga CTR is as class C airspace that has vertical limits of SFC-2500FT and covers the RIX Riga Airport (formerly Riga International Airport). The CTR is of an irregular shape to accommodate for noise abatement practices in a large city (by Latvian standards) such as Riga, as well as to make space for the Aerodrome Traffic Zone (ATZ) of Spilve Airfield. Riga CTR is staffed by Rīga Tower.

Lielvarde CTR

Lielvarde CTR is a class D airspace that is split into sectors A and B which have vertical limits of SFC-1000FT and 1000FT-4000FT respectively. This CTR covers the Lielvarde military base and is also an irregular polygon. 3 sides of it are perpendicular to each other and 1 follows the border of Riga Terminal Maneuvering Area (TMA) Sector B. This CTR is not permanent and may be deactivated at any time (Republic of Latvia AIP EVGA AD 2.17). Lielvarde CTR is staffed by Lielvarde Tower.

Terminal Maneuvering Area (TMA)

Terminal Maneuvering Areas are another type of airspace directly associated with an aerodrome. Typically this is a portion of airspace specifically allocated for handling separation among aircraft that are continuously climbing/descending, i.e. those that have just departed or are about to arrive. TMAs are often split into sectors that may be staffed by different ATCOs to accommodate for large traffic volumes. Same as a CTR, a TMA may be procedural. An ATCO responsible for a non-procedural TMA or its section holds an Approach Control Surveillance (APS) endorsement, thus the ATC station responsible for a TMA typically holds callsign of “Approach” or “Departure”.

EVRR FIR has only 1 TMA — Riga TMA. This TMA is attached to and associated with the RIX Riga Airport. Riga TMA is class C airspace that is atypically large compared to other European TMAs, it spans more than 120 nautical miles. The TMA is split into 3 sectors: A, B, and C with respective vertical limits of 3000FT-FL285, 1500FT-FL95, and 3000FT-5500FT. Riga TMA is staffed by Rīga Approach and has 2 staffing configurations: a combined Rīga Approach covering sectors A, B, and C on frequency 129.925 MHz, or a 2-sector split with sectors A and C being covered by frequency 129.925 MHz and sector B being covered by frequency 134.850 MHz.

Control Area (CTA)

Control Area is the broadest definition of controlled airspace. Practically, any airspace that does not serve a specific purpose in relation to a controlled airfield is a CTA. Most airspace that an aircraft passes through on its way from A to B is likely a CTA of some kind. It is common for CTAs to follow the lateral limits of the FIR they belong to and/or be split into sectors or areas of responsibility (AoRs). A CTA is staffed by a controller holding an Area Control Surveillance (ACS) endorsement; the ATC station responsible for a CTA or its section typically holds a callsign of “Control”, “Radar”, or “Center” (the latter one applies only to North/South America).

Riga CTA is a class C airspace within the lateral limits of Riga FIR. It is staffed by Rīga Control and has vertical limits of FL95-FL660 and is split into 3 AoR:

• Riga AoR – Sector NORTH (Rīga Control frequency 135.100 MHz)
• Riga AoR – Sector SOUTH (Rīga Control frequency 134.750 MHz / 135.100 MHz)
• Riga AoR – Sector EAST (Rīga Control frequency 133.200 MHz)

An additional secondary frequency is defined for all AoRs — 134.125 MHz which is often used to combine sectors NORTH and SOUTH into a common sector (WEST) on the western side of the FIR. As in most European FIRs, the emergency frequency is 121.500 MHz.

Uncontrolled Airspace

All airspace outside the limits of controlled airspace is uncontrolled. Such airspace can be of class F or G; with the former being used rather rarely, most uncontrolled airspace in the world is of class G. In this type of airspace radar separation and surveillance are not provided to traffic, thus ATC holds no responsibility for separation of traffic. Within uncontrolled airspace Flight Information Service (FIS) is often provided.

In Riga FIR all uncontrolled airspace is of class G and its limits are defined as everything that is not defined as controlled airspace. This airspace is also split into FIS sectors (primarily for defining separate vertical limits and to ensure appropriate frequency range). The FIS frequencies in EVRR are as follows:

• Riga FIS Sector (Riga Information) – 120.225 MHz
• Liepaja FIS Sector (Liepaja Information) – 129.400 MHz

Liepaja Information also functions as an Aerodrome Flight Information Service (AFIS) station for the Liepaja airport.

Aerodrome Traffic Zone (ATZ)

While not all Aerodrome Traffic Zones are uncontrolled, most European ones are. An ATZ is a small portion of airspace, typically of a cylindrical shape extending a few miles around and up to a few thousand feet in a given airfield’s vicinity. The center of the aforementioned cylinder is often located at the Aerodrome Reference Point (ARP) or some other significant feature related to the aerodrome (e.g. the center of the longest runway, control tower, etc.)

There are many airfields with a defined ATZ in Riga FIR; all of them are uncontrolled. Airfields such as Ventspils (EVVA), Spilve (EVRS), and Ādaži (EVAD) have an ATZ. All of them have various vertical and lateral limits, so it is important to read up on relevant details about those airfields before controlling an airspace that includes them or flying into one of them.

Flight Information Zone (FIZ)

As evident from the name a Flight Information Zone is a portion of airspace in which pilots may expect to receive Flight Information Service (FIS). In most cases FIZs are used to divide uncontrolled airspace into FIS sectors (EVRR FIR has 6 FIS sectors with Liepaja FIS Sector also being defined as Liepaja FIZ).

Liepaja FIZ is the only such airspace in EVRR FIR and it is split into 2 sectors. Liepaja FIZ Sector A is situated immediately around Liepaja Airport and has vertical limits of SFC-1500FT, Sector B on the other hand is much larger and in lateral limits is identical to Riga CTA AoR North + Riga CTA AoR South (i.e. the western sector of Riga CTA), it has vertical limits of 1500FT-FL95. The entire FIZ is class G airspace and is serviced by Liepaja Information — an AFIS/FIS station on frequency 129.400 MHz.

Transponder Mandatory Zone (TMZ)

Transponder Mandatory Zones are quite straight forward to understand. As the name suggests, when in such an airspace, aircraft’s transponder must be on; typically mode C or S is required. Technically, any controlled airspace is a TMZ, however there are many cases when such an airspace is defined explicitly in a portion of uncontrolled airspace.

An example of a TMZ in EVRR FIR is Liepaja FIZ, both sectors of which are a TMZ. Riga FIS sectors are also TMZs.

Radio Mandatory Zone (RMZ)

Similarly to a TMZ, it is easy to understand the purpose of a Radio Mandatory Zone by its name. When in such an airspace, communications on a certain frequency are a requirement for all traffic. Said communication may be either in the form of a CTAF or two-way communications with ATC.

An example of an RMZ in EVRR FIR is Liepaja FIZ, both sectors of which are an RMZ. The relevant frequency for Liepaja FIZ is Liepaja Information on 129.400 MHz. Riga FIS sectors are also RMZs. For them the relevant frequency depends on the current ATC staffing; the frequency to use should be determined in the following priority order (from highest to lowest):

• Rīga Information (120.225 MHz, all sectors)
• Rīga Approach (134.850 MHz, only sector 1)
• Rīga Approach (129.925 MHz, sectors 1, 2, and 5)
• Rīga Control (133.200 MHz, only sector 3)

Additional Notes and Further Reading

Technically, airspace above FL660 is also subject to Flight Information Service, however in the modern day no traffic is ever present in that airspace except for some super-advanced military jets. Therefore the relevant frequencies and procedures for this part of airspace are omitted from this knowledgebase.

For more information, detailed lateral limits of airspaces, and other data on EVRR FIR, see Republic of Latvia eAIP, published by Latvijas Gaisa Satiksme (LGS).