The Language of Aviation


While the international language of aviation is English it may seem at times that FAA controllers are speaking a foreign language with the unique phraseology, acronyms, and fast pace of the conversation making it hard for the unfamiliar to follow.  The International Civil Aviation Organization (ICAO) globally and the FAA in the United States governs this language and have instituted very strict rules about communication that cover the responsibilities of both pilots and controllers.  The object is to be as efficient as possible when speaking using the fewest possible words to convey a direction or confirm an instruction as outlined in ICAO Standard Phraseology:  A Quick Reference Guide for Commerical Air Transport Pilots.  Brevity in communication is critical especially in congested airspace like that over the Bay Area where controllers are handling dozens of flights at a time and every second is critical. 

To ensure that communication is clear and there are no mistakes in interpretation of instructions which could cause a deadly accident aviation uses a phonetic alphabet to avoid confusion of similar letters in the alphabet like B and D.  This system was adopted by ICAO in 1956.  You will hear this phonetic alphabet anytime you listen to air traffic control conversations such as LiveATC.  Below is a chart that lists the letters and their corresponding phonetic name.

LetterPhonetic PronunciationLetterPhonetic Pronunciation

In addition to phonetic alphabet aviation also uses phonetic pronunciations of numbers as shown in the chart below, again this is done to avoid confusion over the radio.  Although in the U.S you are not likely to hear many of these with the exception of Nin-er.  In countries, where English is not the first language it is very common to hear these phonetic pronunciations.

NumberCode WordPhonetic Pronunciation

Aviation Codes Decoded

Air traffic controllers and pilots also use lots of codes in their digital communication.  There are codes for airports, airlines, and even codes to identify different aircraft types.  But what do they all mean?  First, it's important to understand that the codes used by pilots and ATC were established by ICAO and are completely different from the International Air Transport Association (IATA) codes used by airlines to manage passenger bookings. 


The three-letter IATA airport codes are what most people outside of aviation are most familiar with.  These are the three-letter codes that you see on your boarding pass, bag tags, or online when you are booking a flight such as LAX, ORD, or JFK.  But ATC and pilots use a very different set of codes when piloting the airplane and for a very simple reason.  IATA codes are only used at airports that provide commercial airline service which to date numbers somewhere around 2,500 worldwide but IATA currently lists 9,089 active facility codes on its website.  This figure includes train stations as well. 

Sample Airline Bag Tag with Final Destination of Montego Bay, Jamaica (MBJ)

According to the FAA's 2019-2023 National Plan of Integrated Airport Systems (NPIAS), there are currently 506 commercial air service airports that process at least 2,500 revenue passenger boardings per year and receive scheduled passenger service in the U.S.  By contrast, the total number of airports in the United States identified by the FAA in 2019 was 19,627 as broken down in the table below.

Type of FacilityTotal U.S. FacilitiesPrivate Use FacilitiesPublic Use FacilitiesExisting NPIAS Facilities
Seaplane Base50729221538

Although not all of these airports have an assigned ICAO code, in fact, ICAO as of 2016 listed 10,000 airports worldwide with a unique four-letter code assigned.  By contrast the CIA in its World Fact Book identified 41,820 airports worldwide.  This number includes abandoned and closed airports as well as grass strips.

Four letter ICAO airport codes are assigned based on regions while IATA codes have no, regional association and often take the name of the cities where they are located.  As mentioned above IATA codes also include train stations as well.  The structured assignment of ICAO airport codes allows users to discern not only the airport region but also the country of origin.  The first letter of an ICAO code denotes the general region, as shown in the map below. 

ICAO Airport Code Regions "First Code Letter"

Some countries such as the United States due to its geographic size and the sheer volume of airports have their own primary letter "K" which isn't shared with any other country, however, most other countries share a regional code.  Australia "Y", and Canada "C",  also have their own individual letters assigned. 

The U.S., in fact, uses multiple prefixes.  The "K" prefix is used for all airports within the 48 contiguous states, while Alaska, Hawaii, and all American territories in the Pacific like Guam use the "P" prefix.  All U.S. territories in the Caribbean like Puerto Rico and the United States Virgin Islands use the "T" prefix.  The "P" and "T" prefix unlike "K" is not exclusive to the United States and is shared with other countries in the region.

Most U.S. Airports four-letter ICAO code is similar to its three-letter IATA  code but with the addition of the K prefix such as SFO (IATA) and KSFO (ICAO).  K was chosen by the U.S. as it prefix because half the radio station identifiers in the U.S. at the time began with K. 

Airports in Alaska and Hawaii don't follow this logic and instead follow the standard naming logic for ICAO codes in which the second letter of the code designates the country.  In the case of Alaska and Hawaii which are U.S. states, they have been assigned the following two-letter codes:  Alaska ("PA", P for Pacific, and A for Alaska and Hawaii "PH", with P for Pacific and H for Hawaii.  So Juneau airport in Alaska whose IATA code is JNU has an ICAO code of PAJN.  Similarily Kona Airport in Hawaii has an IATA code of KOA but an ICAO code of PHKO.

All other regions of the world follow the two-letter pattern where the first letter identifies the airport region and the second the country.  For example "EH" denotes that the airport code is in the European region and the country of the Netherlands.  This naming strategy makes it easier for users who may be unfamiliar with a particular airport code to narrow it down to the region and country.  For example the ICAO code EHAM, without knowing the airport it belongs to you can deduce that it is in the European country of the Netherlands.  EHAM is, in fact, the ICAO code for Amsterdam Schiphol Airport, and its IATA code is AMS.  The ICAO Airport Code Table identifies the unique two-letter ICAO code prefix associated with every country listed by region. 

The letters I, J and X are not currently assigned and Q is reserved for international radio communications and other non-geographic special uses.  Code ZZZZ is pseudo-code used in flight plans for airports with no ICAO code assigned.


Every airline operating in the world also has a unique two-digit alpha/numeric IATA code and a three-letter ICAO code to identify it.  Unlike the airport codes, there is no regional association tied to the codes.  Older more established carriers have IATA and ICAO codes that closely match their name, making them easier to identify who the airline is, while newer airlines have been assigned less obvious codes that are not similar to their name. 

The two-digit IATA codes are used by the airlines for all non-flying aspects of the airline including reservations, ticketing, timetables, and communications between airport stations.  The three-letter ICAO codes are used for all flying related tasks like flight plans, ATC tracking and identification, and any other services related to the direct operation of flights.  For example Spirit Airlines has an IATA Code of "NK" and an ICAO code of "NKS."

ICAO issued the first two-letter airline codes in 1947, prior to this date airline codes didn't exist and weren't used.  In the early 1950s, IATA began using the same two-letter ICAO codes to identify member airlines.  Then in 1982 due to the expanding number of airlines, ICAO introduced three-letter airline codes while IATA retained the two-digit alpha/numeric codes.  This dual code system persists to the present day.


In addition to the airline codes for U.S. registered carriers the FAA as stated in JO 7340.2E also assigns every airline a unique ICAO callsign (telephony designator) which is used to identify the airline in all ATC communications.  This radio callsign sometimes is the same or very similar to the name of the airline, but in other cases can be very different. 

For example the radio callsign for British Airways is SPEEDBIRD.  This callsign was originally assigned to British Overseas Airways Corporation (BOAC) which was the British International Flag Carrier.  British European Airways (BEA) a separately administered airline was tasked with operating all British domestic and European flights.  In 1971 an act of Parliament merged BOAC and BEA to form British Airways and the new airline retained the SPEEDBIRD callsign from BOAC.  

Callsigns help to expedite radio communications and ensure there is no confusion between the aircraft and ATC about what instructions are directed at which aircraft.  Callsigns must be easily and phonetically pronounceable in English.  For example, Air France's callsign "Airfrans", 'frans' is the phonetic spelling of 'France'.  The Airline Code Table contains an alphabetic listing by the airline name of common operator codes and radio callsigns that you might expect to see and hear in the skies over the Bay Area. 

Operators that do not have an FAA assigned callsign are referred to by their aircraft's unique tail number in ATC radio communications.  So N007JB, a Cesnna 182 aircraft, would be referred to by ATC as Zero-Zero-Seven-Juliet-Bravo.  The leading N is dropped as that is the ICAO aircraft registration prefix for the United States, commonly called the "N  Number".  Once radar contact is established with the aircraft it is common for ATC to refer to the aircraft by the aircraft type and the last three alpha/numeric characters of its N number.  So the controller would issue instructions using Cessna Seven-Juliet-Bravo as the short callsign in reference to N007JB.

Air Taxi operators in the U.S. that do not have a registered FAA callsign use the "T" prefix before their tail number to identify them as air taxi flights.  For example, TN007JB would indicate to ATC that this is an air taxi flight.  However, the pilot would still identify his aircraft as Zero-Zero-Seven-Juliet-Bravo in all radio communication.

All air ambulance operators that do not have an FAA registered callsign that are in the progress of a flight that is a critical medical transport where life is threatened and speed is essential use the "L" prefix before their tail number and append "MEDEVAC" to their callsign.  Critical medical flights include response to an accident scene, carrying critical patients, organ donors, organs, or other urgently needed lifesaving medical materials.  For example, LN007JB would indicate to ATC that this aircraft is involved in medevac transport and the flight needs priority handling.  To inform other aircraft of its special status ATC would reference the aircraft as Medevac 007JB.  The rules concerning the acceptable use of the "MEDEVAC" callsign are spelled out in FAA Order JO 7110.6060.


All fixed-wing aircraft and helicopters flying around the world are required by law to obtain and display a unique registration number on their aircraft, which is very similar to a car's license plate.  The number must also appear on the aircraft's certificate of registration issued by the FAA for U.S. registered airplanes.  A valid certificate of registration must be onboard the aircraft at all times.  An airplane can not have dual registration in two countries at the same time.  Each country is responsible for establishing the registration process, maintaining the requirements, and enforcing the statute. 

Just like the ICAO airport codes each country has a unique one or two-character registration prefix.  The aircraft's registration code identifies the country where the airplane is legally registered.  No two codes can be the same, but codes can be transferred to a new aircraft when the aircraft is sold, written off (damaged beyond repair), or retired from service to be parted out.

The first use of aircraft registrations was based on radio callsigns allocated at the International Radiotelegraph Convention in London in 1912.  The format established was a single letter prefix followed by four alpha characters such as (A-BCDE).  Larger countries like the United States were allocated their own single letter prefix while smaller countries such as the Netherlands had to share a prefix but were given exclusive use of the first letter of the suffix.

The Paris Convention of 1919 also called the "Convention Relating to the Regulation of Aerial Navigation" was the first international convention to specifically address international aerial navigation.  At this conference the International Commission for Air Navigation, the forerunner to ICAO established uniform standards that were adopted worldwide to end the patchwork of national regulations including making changes to the aircraft registration regulations.  The convention established four basic principles and a document that included nine chapters.  The agreement that came out of the conference stipulated that nationality marks were to be followed by a hyphen then a group of four letters that must include a vowel with Y being considered a vowel. 

At the International Radiotelegraph Convention in Washington D.C. in 1927 the rules concerning registration markings were further revised.  ICAO took over management of the registration system in 1947 and while numerous changes and modifications have been made to the registration system over the years the basic alphanumeric system and country codes remain in use to this day. 

Article 20 of the Chicago Convention on International Civil Aviation published in 1944 outlines the specific requirements for registration of aircraft engaged in international air navigation, specifically the identification of the plane's nationality and placement of the registration number.  Annex 7 to the Chicago Convention further describes the definitions, location, and measurement of nationality and registration marks. 

The United States is assigned the sole use of the N prefix as stated in the previous section, but most countries like ICAO airport codes share a prefix but have exclusive use of the first letter of the registration suffix. For example the Netherlands uses PH as its registration prefix, with the "P" prefix being shared with other countries but the H being exclusive to Dutch-registered airplanes.  The photo below illustrates the ICAO requirements for displaying and aircraft registration.  The registration code PH-KCG and Dutch flag identify this MD-11 aircraft as being registered to KLM Royal Dutch Airlines in The Netherlands.

PH-KCG was the registration of a now-retired KLM Royal Dutch Airlines MD-11

The ICAO Aircraft Registration Prefixes contains an alphabetic listing of each country's unique code.


Every aircraft type used in commercial airline service has an aircraft type designator which is a unique three (IATA) or four-character (ICAO) alphanumeric code that is used by the airline for different purposes.  four-character ICAO codes are published in ICAO Document 8643 Aircraft Type Designators and are used by ATC and airline operations for flight planning and in-flight management purposes.  The ICAO aircraft type is used to distinguish between aircraft types and variants that have different flight performance characteristics that affect ATC separation requirements for landings and takeoffs in relation to other aircraft types based on the aircraft's maximum takeoff weight (MTOW) and maximum landing weight (MLW). 

Three character IATA aircraft codes which are published in Appendix A of IATA's annual Standard Schedules Information Manual (SSIM) are used for all non-flying aspects of the airline business such as computer reservation systems and ticketing.  However, unlike the ICAO codes, the IATA aircraft codes provide more detailed information that distinguishes between similar variants and identifies their role either passenger or freight, which are important from a commercial operations perspective.  For example, the ICAO code for the Boeing 767-300 is B763, however, there are multiple IATA codes for the same ICAO type:  763 (Passenger), 76W (Passenger with Winglets), 76Y (Freighter). 

Why doesn't the ICAO aircraft code provide more details?  The answer is simple, from an ATC perspective it doesn't matter if the 767 has winglets or is carrying freight or passengers the only thing that matters is the landing speed, and MTOW of the type for separation considerations.  So for ATC purposes, this additional information is not necessary. 

ICAO codes may sound confusing but there are similarities in aircraft families.  For instance, the Boeing 737NG series which consists of the 737-600, 737-700, 737-800, and 737-900/ER models and are represented by the ICAO codes B736, B737, B738, B739.  The increasing numbers tell you two things first the larger the number the longer the aircraft is and correspondingly the greater its seating capacity.  Below is a breakdown of the differences between the various 737NG types comparing their length from nose to tail and all coach seating capacity with the current U.S. average seat pitch of  30 in.