Pronunciation of Words And Five Letter Naming Codes

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Pronunciation of Words And Five Letter Naming Codes

55TH ANNUAL CONFERENCE, Las Vegas, USA, 14-18 March 2016

WP No. 162

Pronunciation of Words and Five Letter Naming Codes

Presented by TOC


Standardizing the pronunciation of alphabets, words and phrases has provided a simpler language set between ATC and Flight Crew with the capability of mitigating the risk of misunderstanding in communication. As reasonable as the Globalization of the ICARD system, the rules guiding the allocation of waypoints need finetuning for safety enhancement necessitating the focus of this paper.



1.1  Misunderstandings between ATC and pilots are a notable cause of safety incidents, and can lead to confusion on the flight deck, increased ATC/Pilot workload and execution of incorrect clearances.

1.2  Of the many factors involved in the process of communication, phraseology is perhaps the most important because it enables us to communicate quickly and effectively despite differences in language by reducing the opportunity of misunderstanding.

1.3  Standard phraseology reduces the risk that a message will be misunderstood and aids the read-back/hear-back process so that any error is quickly detected. Ambiguous or non-standard phraseology is a frequent cause or contributory factor in aircraft accidents and incidents.

1.4  The proliferation of PBN procedures, among other factors, has lead to an increased usage of 5LNC waypoint names from a finite database.


2.1 History of Phonetic Alphabets

2.1.1 The first internationally recognized phonetic alphabets was adopted by the International Telecommunication Union (ITU) in 1927. In 1932 the ITU made some changes to the existing alphabets and then adopted by the International Commission for Air Navigation, the predecessor of ICAO, to be used in Civil Aviation until WWII. They were:


(N)New York
(Y)Yokohama and

2.1.2  Along the line saw some more changes not intended to mention here which were made due chiefly to unintelligibility under poor receiving conditions leading to the final version adopted by ICAO on 1st of March 1956.

2.1.3  The current standard ICAO phonetic alphabets are:

























(Y)Yankee and,


2.1.4  These are the numbers and their pronunciation:

0 (ZE-RO)

1- (WUN)

2- (TOO)

3- (TREE)

4- (FOW-er)

5- (FIFE)

6- (SIX)

7- (SEV-en)

8- (AIT)

9- (NIN-er)

Decimal- ( DAY SEE MAL)

Hundred- (HUND- red)

Thousand- (TOU-SAND)

2.2 Human Communication

2.2.1  Communication is simply the act of transferring information from one place to another, where this be vocally, written, visually or non-verbally.

2.2.2  Being able to communicate effectively is the most important of all life skills, often essential to solving problems that inevitably occur both in our private and professional lives.

2.2.3  Four communication skills include: Thinking, Listening, Speaking and Non-verbal. Communication between ATC, adjacent ATS units and the flight crew excludes mostly the non-verbal form of communication due to the reduced reliance on visual tools of communication.

2.2.4  Thinking, among other definitions and within the focus of this paper, is the employment of one’s mind rationally and objectively in evaluating or dealing with a given situation.

2.2.5  Speaking is the action of conveying information or expressing one’s feeling in speech, or in other words, the vocalized form of human communication.

2.2.6  Listening is a vital interpersonal communication skill. When we communicate we spend 45% of our time listening. Listening is not the same as hearing. Listening is a skill. Effective listening helps to avoid misunderstandings. Reflection and clarification are common techniques used to ensure that what heard and understood is what was intended.

2.2.7  Clarity is an inevitable quality of effective communication that has to do with dissemination of comprehensible and unequivocal information. The dissemination of a meaningful idea is the ultimate goal of communication.

2.3 Ambiguity in Pronunciation

2.3.1  Aviation English training requires a practice of both listening and speaking, which form the main part of the ICAO tests, so pronunciation is essential. Pronunciation is of course a fundamental part of language learning and allows the speakers to express themselves coherently and accurately. Pronunciation involves the following:

  • Stress- The emphasis of words or parts of words (syllables).
  • Rhythm- The speed of communication.
  • Intonation- The high, middle and low levels of speech.

2.3.2  Due to the fact that what sound your front mouth/lips makes as opposed to the back of the throat, it is advisable that a focusing on repeating the words over and over a period helps in perfecting pronunciation of words.

2.3.3  Ambiguity is defined as an attribute of any concept, idea, statement or claims whose meaning, intention or interpretation cannot be definitely resolved according to a rule or process consisting of a finite number of steps.

2.3.4  Literally, a word, phrase or a sentence is ambiguous if it has more than one meaning. Context may play a role in resolving ambiguity. For example, the same piece of information may be ambiguous in one context and unambiguous in another.

2.3.5  There are two types of ambiguity:

  • Lexical ambiguity refers to the ambiguity of individual words or phrase that can be used in different contexts to express two or more different meanings.
  • Structural ambiguity, also refers to as syntactic ambiguity, is a situation where a sentence may be interpreted in more than one way due to ambiguous sentence structure.



2.5  In route planning and design, two activities are essential:

  • the allocation of Route Designators, uniquely identifying individual routes and;
  • the allocation of 5LNC codes, uniquely identifying designated point, forming part of a route.

2.6  Annex 11, Appendix 2, paragraph 3.1. stated that: “Where a significant point is required at a position not marked by the site of a radio navigation aid, the significant point shall be designated by a UNIQUE five-letter pronounceable “name-code””… usually shortened as 5LNC.

2.7  An ATS route is a specified route designed for channelling the flow of traffic as necessary for the provision of air traffic services. The term “ATS route” is used to mean variously, airway, advisory route, controlled or uncontrolled route, arrival or departure route, etc.

2.8  An ATS route is defined by route specifications which include an ATS route designator, the track to or from significant points (waypoints), distance between significant points, reporting requirements and, as determined by the appropriate ATS authority, the lowest safe altitude.

2.9  Significant points shall be established for the purpose of defining an ATS route and/or in relation to the requirements of air traffic services for information regarding the progress of aircraft in flight.

2.10 Modern air navigation systems use longitudinal and latitudinal designated points, identified either by a unique pronounceable or alphanumeric Five Letter Name Code (5LNC), which are drawn from a set of predefined five letter combinations generated by ICAO and the FAA in the 1970’s.

Background To ICARD (International Code and Route Designator) System

2.11 ICAO and the FAA, in the 1960’s, set up a list of 140,000 five letter combinations of five- letter name-codes (5LNC). This list was then split and distributed to the various ICAO Regional offices throughout the world. These reserve lists have served as the database for 5LNC allocation by the ICAO Offices with the objective of world-wide unique allocation to enable unambiguous designation of significant points.

2.12 The ICARD 5LNC application is intended to facilitate the management of Five Letter Name Codes (5LNC).

2.13 Before ICARD, route planners had little chance of knowing whether their request of a proposed code would be accepted or not. In addition, relying on surface mail, proved to be a very time- consuming method of information exchange between ICAO and its users.

2.14 5LNC were originally reserved and chosen from the ”The Green Book”. The consequence of this manual recordings introduced many duplicates between region. Coordinates mistakes, also found their way in this manual 5LNC data base.

2.15 With the ICARD 5LNC Database, authorized airspace planners have access to an ICAO database tool that provides the ability to make on-line requests for five letter name codes. The ability to query this database and have immediate information on 5LNC availability, greatly enhances the safety and efficiency of airspace planning. It prevents the duplication of 5LNC’s and therefore enhances safety by ensuring a unique 5LNC for airspace planning purposes.

Duplicate Resolution Rules are defined as follows:

2.16 Priority is given to 5LNC that were allocated through the official channels.

2.17 The 5LNC ICAO Official Register is designed in such a way that there will never be more than one 5LNC loaded in ICARD through the official channels. AIP alignment codes will be marked as Non-ICAO.

2.18 If all 5LNC duplicates were allocated outside the official channels, priority is given to the code that was allocated at the earliest date, if such a date is available; otherwise the ‘Priority List’ rule defined below is applicable.

2.19 Priority List:

  • The following characteristics will receive priority:
    • i. FIR Boundary point;
    • ii. SID/STAR;
    • iii. Major en-route crossovers;
    • iv. Upper airspace;
    • v. Lower airspace.
  • In Resolving conflicts If any of the previous rules could not allow resolving the 5LNC duplicate, the final judgment will be made by ICAO.

Proposal by EUROCONTROL on Resolution of like-sounding Waypoints Names

2.20 The applicability of this proposal is to prevent similar sounding ICARD waypoints names within a radius of 500 nautical miles.The following are typical examples of waypoints names in use within one FIR (Kano) that violate the proposal for prevention of similar sounding waypoints names.

2.21 The proposal is presented in form of a set of rules:

2.21.1 The first rule states that no two or more waypoints names shall

have four similar letters in the same position in its name within a radius of 500nm. The following set of waypoints names in the Kano IFR violated this rule:

  • IKROP (05°46’44.00” N, 008°52’27.50” E) and IKROL (07°25’24.55” N, 007°51’36.60” E). The distance and bearing between these two waypoints are 115nm and 329°, respectively.

2.21.2  The second rule states that the last three (i.e. the third, fourth and fifth) letters of two or more waypoints names shall not be similar within a radius of 500nm. The following set(s) of waypoints names in the Kano IFR violated this rule:

  • ILBOX (07°36’48.00” N, 007°09’36.00”) and UGBOX (13°07’24.00” N, 006°49’00.00” E). The distance and bearing between these two waypoints are 330nm and 357°, respectively.
  • ULSIX (07°30’06.00” N, 007°35’48.00” E) and DESIX (07°44’23.00” N, 004°34’00.39” E). The distance and bearing between these two waypoints are 190nm and 094°, respectively.
  • IKROL (07°25’24.55” N, 007°51’36.60” E) and SEROL (11°35’52.11” N, 004°34’00.39” E). The distance and bearing between these two waypoints are 320nm and 324°, respectively.

2.21.3  The third rule states that the first, third and fifth letters of two or more waypoints shall not be similar within a radius of 500nm. The following set(s) of waypoints names in the Kano IFR violated this rules:

  • GANDA (09°28’46.26” N, 003°10’00.60”E) and GANLA (13°45’06.00” N, 008°19’48.00” E). The distance and bearing between these two waypoints are 397nm and 050°, respectively.
  • EDENI (08°05’46.25” N, 009°03’08.79” E) and EPEGI (08°38’42.00” N, 008°07’06.00” E). The distance and bearing between these two waypoints are 64.8nm and 121°, respectively.

2.21.4  The fourth rule, although stated that the second, third and fourth letters of two or more waypoints shall not be the same within a radius of 500nm, recorded no waypoints within the Kano FIR that flouted this rule. However, of note is the existence of some waypoints that weren’t affected by these rules but whose similarity, in my opinion, is a source of concern. Just to mention one set:

  • LINOX (04°56’44.30” N, 007°45’57.40” E) and LISOX (10°19’48.03” N, 005°55’15.87” E). The distance and bearing between these two waypoints are 341nm and 161°, respectively. They seem not to flout any rule, but the similarity and probable ambiguity between them, in my view, elicit the need for a new rule.

Sustainability of the waypoint naming system

2.22 No study or projections have been undertaken to assess the medium to long term sustainability of the current waypoint naming system (ICARD). It is not known how quickly the database is being used, how many duplicates exist or whether the 5LNC system will be able serve the industry into the future.

2.23 Traffic growth and the publication of new air routes, implementation of PBN procedures, and a lack of recycling of redundant waypoints all contribute to a growing use, and perhaps an accelerating exhaustion of the waypoint database

2.24 Pronouncable names need only be required for waypoints that are utilised in voice communications, whether that is air-ground (eg. VHF/HF), or ground-ground (ATS Coordination). One possibility for extending the life of the ICARD/5LNC system is to restrict the use of pronouncable names to waypoints that are used in voice communications.

2.25 Additionally, study is required to ascertain whether the current system is sustainable and whether guidance material for waypoint naming would contribute to greater clarity and reduced misunderstanding in ATC/Pilot communications.


3.1  Many problems of communication stem from the lack of knowledge the parties have about each other. The teamwork reflected in communication between pilots and controllers is a critical component of the air traffic system because it provides the system’s flexibility. Most controllers are not pilots and most pilots are not controllers. Instead of just having impersonal radio contact, it has proved worthwhile for pilots and controllers to observe each other at work. The more they learn about each other, the easier it is to recognize and discuss common interests.

3.2  Amongst controllers there is insufficient awareness of the pervasiveness of the miscommunication problem and its various manifestations. The insidiousness of some of these requires that controllers be provided with a deeper insight into the structures of language and the way which phrases and words can be misinterpreted

3.3  Evidence suggests that voice transmissions between air traffic controllers and pilots are a particular problem in international airspace and that pilots may not understand messages due to the influence of different accents when using English. Results support that communication errors, defined by incidents of pilots misunderstanding, occur significantly more often when speakers are both non-native English: messages appearing to be more complex, and especially when numerical information is involved.

3.4 Study into the sustainability of the current system is required. This may necessitate the development of alternative or replacement naming conventions.

3.5 The life of the ICARD/5LNC system can be extended by prudent use of remaining resources, including restriction of pronounceable names for waypoints utilised in voice communications.


It is recommended that:

4.1 The Executive Board urges ICAO to investigate the sustainability of the existing 5 Letter Name Code system.

4.2 The Executive Board investigates the development of guidance material for waypoint naming.

It is recommended that IFATCA Policy is:


Pronounceable names should be reserved for waypoints that are used in voice communications.


Aviation Knowledge WIKIdot

ICAO Annex 11 – Air Traffic Services

Miscommunications in Air Traffic Control, David McMillan B.App.Sc., Grad.Dip.Ed., M.Ed.

(PDF) EUROCONTROL Duplicated and like-sounding 5LNC

(PDF) Duplicated and like-sounding 5LNC in ICAO EUR/NAT region

Last Update: October 1, 2020  

January 24, 2020   707   Jean-Francois Lepage    2016    

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