What Is a Flight Information Region (FIR)? How FIRs Work, What the Four-Letter Codes Mean, and Why Every Airspace Closure Is Written in Them

Every airspace closure you have ever read about was written in a language of four-letter codes and the phrase flight information region. When Iran's airspace closes, the notice says Tehran FIR, OIIX. When the FAA bans US carriers from flying over Iraq, the rule names the Baghdad FIR, ORBB. When EASA publishes a conflict-zone bulletin, the airspace it describes is an FIR, or a slice of one, and the map on a flight-tracking site is drawn in FIR outlines, not national borders. If you have wondered what a flight information region actually is, this guide explains it from the ground up: what the term means, who runs one, why the boundaries look nothing like a political map, how to decode the codes, and what to look for when an FIR appears in a NOTAM or a travel advisory.

What is a flight information region?

A flight information region, or FIR, is a defined block of airspace within which a single authority is responsible for two basic services to every aircraft inside it: flight information service, which means passing on weather, traffic and hazard information, and alerting service, which means noticing when an aircraft is overdue or in trouble and setting search and rescue in motion. The definition comes from ICAO, the UN aviation agency whose standards every member state has agreed to follow, and it has been part of the international system since the 1940s.

The simplest way to picture it: the whole sky, from the ground to the edge of space, is cut into named regions so that at any moment, at any point on Earth, exactly one organisation is answerable for knowing who is up there and helping if something goes wrong. There are no gaps. Even the middle of the Pacific belongs to someone's FIR.

Inside most FIRs there is also air traffic control, provided by an area control centre, but control is a separate service layered on top. In busy airspace the FIR and the controlled airspace are nearly the same thing; over remote ocean or desert there may be large volumes of an FIR where nobody is actively separating traffic and aircraft follow procedural rules instead.

Why FIR boundaries do not follow national borders

This is the part that confuses most people. A country owns the airspace above its territory, but the FIR it operates often stretches far beyond that, or stops short of it. Three things cause the mismatch.

First, the high seas belong to nobody, so the airspace over oceans is handed out by ICAO regional agreement to whichever state is best placed to provide the service. That is why the North Atlantic is divided between the Shanwick FIR (EGGX), run from the United Kingdom, the Gander FIR (CZQX), run by Nav Canada, and the Santa Maria FIR, run by Portugal, even though no one owns the water underneath. A flight from London to New York spends most of its time in airspace that is British or Canadian for aviation purposes and international for every other purpose.

Second, small or neighbouring states sometimes pool their airspace into one FIR run jointly. The Roberts FIR in West Africa covers Liberia, Guinea and Sierra Leone from a single centre in Monrovia. Large states, by contrast, split their territory into several FIRs: India has Mumbai, Delhi, Chennai and Kolkata; Russia has more than a dozen.

Third, boundaries are drawn for traffic flow and radar coverage, not for tidiness, so an FIR can have a corner that juts into a neighbour's territory by agreement, or a strip along a coast delegated to the country next door. When two states disagree about who should run an FIR, the dispute can last for decades and shows up in the charts as overlapping claims.

The practical consequence for travellers: when a country closes its airspace, what actually closes is its FIR, or the part of it the state controls. That can include a stretch of sea or a corridor that was never in the headlines, which is why a closure sometimes affects routes that do not appear to cross the country at all.

FIR and UIR: the upper and lower layers

Many states divide their airspace vertically as well. The lower part keeps the name FIR and the airspace above a set altitude becomes an upper information region, or UIR. The split altitude is published in each country's aeronautical information publication; in much of Europe it is at flight level 245, roughly 24,500 feet, though it varies. The point of the division is operational: the low-level airspace is busy with departures, arrivals and small aircraft and needs to be managed in small pieces, while cruising traffic at 35,000 feet can be handled in bigger blocks by a different centre.

For passengers the distinction rarely matters, but it does explain one odd thing you will see in notices: a closure or restriction that applies only above or only below a certain level. A state can keep its lower airspace open for domestic flights while restricting the upper airspace that overflights use, or the other way round.

Decoding the four-letter codes

Every FIR has an ICAO location indicator, a four-letter code from the same system that names airports. The first letter identifies a world region and the second usually identifies the country; the last two name the specific centre. Once you know a handful of first letters, codes in NOTAMs stop looking like noise.

• O is the Middle East and parts of South Asia: OIIX is Tehran FIR (Iran), ORBB is Baghdad FIR (Iraq), OSTT is Damascus FIR (Syria), OJAC is Amman FIR (Jordan), OMAE is the Emirates FIR, OEJD is Jeddah FIR (Saudi Arabia), OPKR and OPLR are Karachi and Lahore (Pakistan), OAKX is Kabul FIR (Afghanistan).
• L is southern Europe and the eastern Mediterranean: LLLL is Tel Aviv FIR, LCCC is Nicosia FIR (Cyprus), LTAA and LTBB are Ankara and Istanbul (Turkey).
• E is northern Europe: EGTT and EGPX are London and Scottish FIRs, EGGX is Shanwick Oceanic, EDWW, EDGG and EDMM are the German FIRs.
• U is Russia and most of the former Soviet Union: UUWV is Moscow FIR, URRV is Rostov FIR, UKBV is Kyiv FIR (Ukraine, closed since February 2022).
• H is north-east Africa: HECC is Cairo FIR, HSSS is Khartoum FIR (Sudan).
• V is South and South-East Asia: VABF is Mumbai FIR, VIDF is Delhi FIR, VOMF is Chennai FIR, VECF is Kolkata FIR.
• K is the contiguous United States and C is Canada: KZNY is New York, CZQX is Gander.

How to read an FIR in a NOTAM or a conflict-zone bulletin

Airspace closures and restrictions are published as NOTAMs, and each NOTAM is filed against an FIR. The code appears in the Q-line near the top, for example Q) OIIX/QRAXX/..., which tells you the notice applies in Tehran FIR. The body then describes the area: the whole FIR, a named sector, a set of coordinates forming a polygon, or a band of altitudes. If you have not read one before, our guide to [reading a NOTAM](/blog/what-is-a-notam-how-to-read-airspace-closure-notices) walks through an example line by line.

Regulators' advisories use the same vocabulary. The FAA's prohibitions and background notices for US operators are written per FIR (Baghdad FIR, Tehran FIR, Kabul FIR, and so on), and EASA's Conflict Zone Information Bulletins name the FIR in the title and then recommend what operators should do inside it, sometimes down to specific altitudes or sub-areas. That is why the FIR is the right unit to search for when you want to know whether a route is affected: a country name will find news stories, an FIR code will find the actual notice. We explain the EASA bulletins in [EASA conflict-zone bulletins explained](/blog/easa-conflict-zone-bulletins-middle-east-explained).

One caution when reading them: a bulletin about an FIR does not mean the entire FIR is dangerous or closed. It is common for a notice to cover a portion, for instance the part of an FIR near a border, while traffic continues normally elsewhere in the same region. Check the coordinates and altitudes before assuming a whole country is off limits.

Why airlines plan in FIRs, and what it means for your route

Airlines pay overflight charges per FIR, file flight plans that list every FIR boundary crossing with an estimated time, and hand off from one control centre to the next at those boundaries. When a flight is rerouted around a closure, the planners are really choosing a different sequence of FIRs. Avoiding Tehran FIR on a Europe-to-India flight, for example, means routing through the Gulf FIRs to the south or through the Caucasus and Central Asian FIRs to the north, each with its own charges, winds and congestion. Our guides to the [southern corridor](/blog/southern-corridor-egypt-saudi-arabia-flight-routes) and the [northern arc](/blog/northern-arc-flight-routes-europe-asia-caucasus-central-asia) describe those alternatives FIR by FIR.

This is also why a flight-tracking map shows FIR outlines rather than borders. If you want to check whether your own flight crosses a region in the news, the method in [how to check if your flight avoids conflict zones](/blog/how-to-check-if-your-flight-avoids-conflict-zones) uses the FIR outlines directly, and the [Tehran FIR explainer](/blog/tehran-fir-flight-information-region-explained) is a worked example of a single region from both the operational and the safety side.

Quick answers

What does FIR stand for in aviation? Flight information region: a block of airspace in which one authority provides flight information and alerting services to all aircraft.

Who decides FIR boundaries? ICAO, through regional air navigation agreements between member states. Each state publishes the detail of its own FIRs in its aeronautical information publication.

Is an FIR the same as a country's airspace? No. A state owns the airspace over its territory; an FIR is a service area that may extend over international waters or be shared with neighbours. Closures are declared for FIRs.

What is the difference between an FIR and a UIR? The UIR is the upper layer of the same region, above a published altitude, usually managed by a different centre for cruising traffic.

What is OIIX? The ICAO code of the Tehran flight information region, which covers Iran and is the region most often named in Middle East airspace notices.