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Air Lines: Aviation Safety and Clear Communication

How does communication between pilots and Air Traffic Control (ATC) improve flight safety and why do misunderstandings sometimes lead to disaster?


Clear communication and understanding are crucial in aviation. Air safety relies heavily on effective communication between pilots and air traffic controllers. Researchers of the School of Philological Studies and the Laboratory for Comprehensive Interdisciplinary Projects (HSE University) have prepared a report analyzing this type of communication and the barriers that can prevent pilots and controllers from understanding each other. They conducted their research as part of an HSE Big Project called ‘ Language Practices’ led by Professor Mira Bergelson.

Lingua Franca

Aviation English is the common language of pilots and air traffic controllers. It was established by the ICAO ( International Civil Aviation Organization ), a UN organization responsible for ensuring the safety of international flights. Everything in Aviation English is standardized, from vocabulary and phraseology (Standard Phraseology should be used) to phonetics. Air traffic personnel have to adhere to specific pronunciations of figures when speaking on the radio, which may be different from Received Pronunciation (a standard form of British English pronunciation). Figures are used to talk about flight and runway numbers, among other things.

For instance, ‘zero’ is pronounced as zee-ro, ‘three' as tree, ‘four’ as fow-er, ‘thousand’ as tou-sand. Aviation also uses the NATO phonetic alphabet, where words represent letters: ‘Alpha’ for ‘A’, ‘Bravo’ for ‘B’, ‘Charlie’ for ‘C’, ‘Foxtrot’ for ‘F’, etc. So, to spell ‘RA 2298’, one says ‘Romeo Alpha too niner ait.’ This is necessary to facilitate communication between pilots and controllers and ensure air traffic safety and efficiency.

Aviation English, Standard Phraseology, and clear and unambiguous messages are all vital to effective pilot-controller communication. All pilots of international flights and controllers at international airports must have at least Level-4 proficiency in Aviation English in accordance with the ICAO 2008 six-level scale. Level 4 is Operational, Level 5 is Extended, and Level 6 is Expert. Level 4 is a requirement for pilots hired to operate international flights. Moreover, pilots are required to prove their English language competence every three years by completing an international test.

The Value of Correct Speech

However, few people can speak perfectly over the radio. Pilots and controllers who are not native English speakers vary in their speaking skills and accents. Even native speakers may occasionally fail to comply with language norms, which can result in mid-flight communication failures: misunderstandings or erroneous interpretations of the other speaker’s words. This, in turn, causes mistakes which can lead to a disaster.

In March 1977, two passenger jets, a KLM flight and a Pan Am flight, collided on the runway at Los Rodeos Airport (Tenerife, Canary Islands). The disaster resulted in 583 fatalities. The fundamental cause of the accident is believed to be a misinterpretation of ATC instructions, leading to pilot error.

In another, fortunately non-lethal incident, a Polish Boeing 737 was heading from Heathrow Airport to Warsaw in 2008. The plane spent almost half an hour circling above the airport because the Polish crew couldn’t understand the controller’s directions due to the pilots’ poor English. Heathrow Airport is typically overcrowded, and such maneuvers could have led to disaster.


In reality, there are many factors that hinder radio communications between pilots and air traffic controllers: from radio interference noise and unintelligibly fast speech to linguistic factors like local accents, pronunciation mistakes (wrong sounds, stresses, intonations), incorrect phrasing, syntax, the use of slang, etc.

There can be all kinds of reasons for these problems. Some plane crews lack listening and speaking skills. Others are not very good at Standard Phraseology. Sometimes, Standard Phraseology is simply not enough because the situation itself is non-standard. But how can a pilot paint an accurate picture while talking on the radio? It becomes necessary to find a workaround, using synonyms or descriptive phases, which may have a critical influence on the situation as it can take much time to do so.

Aerial Brawls

English language skills in Russian aviation also leave much to be desired. There have been incidents where the pilots of international flights have switched to speaking Russian (or a mixture of Russian and English) as they couldn’t reply in proper English or wanted to speed things up. In other cases, controllers and pilots communicated too emotionally (which is also against the rules) and in too many words. The authors of the report detailed below provided an example of quite an expressive dialogue between the pilot of a flight to Bangkok and a Sheremetyevo-based controller.

Air traffic controller: ‘Aeroflot 273, if able, turn right to UBIBA, cleared ILS [Instrument Landing System] two four left [runway].

Пилот: Cleared ILS two four left ‘Aeroflot 273’ [pilots are supposed to repeat the instructions].

Air traffic controller: Turn right to UBIBA, ‘Aeroflot 273’.

Pilot: [switches to Russian] Ahem… a bit later ‘Aeroflot 273’.

Air traffic controller: [switches to Russian] What happened?

Pilot: [in Russian] Very small distance to Air France. They tend to … slow down and we wouldn’t want to circle after a ten-hour flight.

Air traffic controller: [in Russian] I feel for you. But what if everyone decided to direct the air traffic with their thoughts? Turn away, slow down and everything will be fine.

The dialogue was followed by another instance of communication from the same controller. The pilot of another flight was also hesitant about the controller’s instructions, who replied with irritation. ‘Are you telling me who and what directions to head for?’ he asked. The pilot, also unable to help himself, said, ‘You use too many words.’

This shows that communication failures do happen in the sky. These failures are the focus of studies by researchers from HSE University and other educational institutions, including Denis Zubalov, Head of the Language in Aviation project and Assistant Professor of the School of Philological Studies, Anna Akopova, Assistant Professor of Moscow State Technical University of Civil Aviation, and Research Assistants of the Laboratory for Comprehensive Interdisciplinary Projects Arina Andrievskaya, Madina Kade, and Elizaveta Kriukova.

The researchers presented the preliminary results of their study in their report ‘Disrupted Communication in the Sky: the Language Case of Pilots and Controllers’ during the Language Practices workshop of the Big Project. The study encompasses 26 semi-structured interviews with existing and former pilots and controllers.

Negotiation (without) Defeat

Language is by no means the only cause of communication failures or interruptions. According to the researchers, they can result from:

 pilots’ personal qualities (for instance, being unable to handle their emotions)

 equipment operability

 how well they know the locale

 work schedule and heavy workloads

 busy air traffic (traffic at the airport)

 time constraints

 poor radio reception (for instance, due to altitude or landscape) or crowded radio frequencies where those communicating must try to be heard at all costs.

Even when a pilot has good language skills, communication efficiency might be impacted by factors such as a heavy workload or a bad radio connection. Therefore, one of the ICAO rules for controller-pilot dialogue is called a ‘receipt’. This means that:

 Each party (the pilot or the controller) confirms their receipt of the other party’s information using special acknowledgments. The crew must ‘read back’ air safety-related messages and instructions from the ATC (provide a ‘receipt’).

 The air traffic controller must listen to the ‘receipt’ and make sure that the crew has understood the instructions correctly. Prompt measures must be taken in the event of any deviations.

As we can see from the dialogue in Sheremetyevo Airport, the pilot reads back the controller’s instruction. However, there are deviations even from the basic rules. ‘Sometimes, the controller doesn’t let the pilot finish. Some people do not treat the acknowledgment receipts seriously enough. The crew may “cut corners” on acknowledgments, rushing through phrases,’ a pilot with 18 years of flying experience told IQ.HSE.

Radio Communication Failures

The aim of the study was to look into deviations from the ICAO Standard Phraseology and reveal the reasons for disrupted communication. Special focus was given to analyzing communications in Russian civil aviation.

The results of the project will be used to develop recommendations on how to improve communication between pilots and air traffic controllers of different nationalities, as well as to minimize the risks of misunderstandings over the radio.

The main causes of communication failures are as follows:

Thick local accent. Artem, a pilot with 30 years of flying experience, says that ‘Germans have a heavy accent and they can “bark” out their words. They are meticulous and try to keep within the radio communication rules, but it can be difficult to understand them because of their German accent.’ Similar comments were made about Italian, Spanish, French and various Asian accents. ‘There can be some misunderstandings during flights across China as ... some people do not speak English very well there,’ says 48-year-old Anton (30 years of flying experience).

High pace of speech, excessive information. 41-year-old Roman (22 years of flying experience) comments on US English-speaking ATC, saying that ‘They speak fast and say a lot. You only need 30% of what they say, and the other 70% is given for your reference only.’

Misunderstanding of phraseology. Artem, a pilot with 30 years of flying experience, tells a story that happened in Zurich. ‘The traffic pattern there looks like a loop. So we had to make this loop before we landed. The controller’s instruction was ‘Extended orbit’. We understood ‘extended’ to mean make a loop as slowly as possible, make a sweep turn. So that’s what we did.’ However, the outcome was undesirable. ‘We flew into noise sensors. Aeroflot received a complaint,’ he says.

Deviation from Standard Phraseology. According to 25-year-old pilot Boris (2 years of flying experience), this is typical of English-speaking personnel. ‘We are supposed to say one eighteen two when we speak about the frequency 118 and 2, but they breeze past the first figure, they don’t even pronounce it.’ However, native speakers aren’t the only ones to do this.

Slang. Pyotr, a 25-year-old pilot, says that British ATC ‘shorten phrases, use their own words.’ According to some respondents, this is also common among Americans.

Off-topic conversations. Sometimes, one of the speakers tries to find out or share information that is irrelevant to the flight. ‘He wanted to know the city code for London, the phone number. It was mind-boggling. Nobody could understand him,’ says Valya, a 31-year-old air traffic controller.

Lack of experience. ‘You understand every word and the structure, but not what they really mean… Why are they telling us this? What does it mean? Understanding comes with experience and improved listening skills,’ says Pyotr, a 25-year-old pilot. Listening skills can be particularly poor when people are at the beginning their career.

Say Again!

Alexander (26 years old, 4 years of work experience) says that ‘our teacher taught us that pilots must not assume—they must know.’ It means that messages have to be crystal clear and understandable to all parties. The respondents suggest a few solutions to address language problems.

If the ATC instruction is not clear, the pilot must request a repetition by saying ‘Say again’ (or ‘Speak slower and say again’). In some instances, one has to paraphrase the question. ‘We use other words so that they understand us,’ says one of the respondents. General English is used in certain cases to get the message across.

26-year-old Andrey (2 years of experience) points out that ‘There is a nuance here. If one of the crew hears the instruction but another doesn’t, then the latter has to request that the controller repeat it until both crew members have heard everything clearly.’

Equipment can come in handy if the signal is bad. ‘We’ve got a special device that records radio communications. You can ... listen to any part of the communication again at any time to try to… hear better, or you can ask your colleagues what they heard,’ says Sasha, an air traffic controller (25 years old).

Help from senior colleagues is invaluable. They can explain what exactly the controllers ‘meant by a particular phrase,’ says 25 year-old Pyotr. 'A colleague of mine was asked about flight levels … they asked 'odd / even?’ We listened again—it’s easy to do nowadays—and I guessed that he was asking about the odd / even level,' recalls Valya, a 31-year-old controller.

High-altitude Messengers

Attempts have been made to facilitate communication using alternative messaging systems. Controller-pilot Data Link Communiсations (CPDLC) is an air-land communication system used by aircraft crews and controllers to exchange messages. It helps to reduce the burden of voice communications.

25-year-old pilot Pyotr comments on the practice: ‘Nowadays, people try their best ... to simplify communication. New technologies like CPDLC are used by flights over Europe. To put it simply, the ATC gives instructions via a chat dialogue.’ Pilots reply by sending text messages. He adds that ‘this is only possible when you are flying at a high altitude, where radio channels aren’t that busy and the instructions are quite clear and simple.’

Finally, crews should maintain their language skills, both in Aviation and General English. Pilots explain that they read news and watch television in English. 'This is vital,’ Viktor E. told IQ.HSE . ‘When we are abroad, we use every opportunity to speak with English natives. It is important to understand different accents, get used to them.’ It is true that heavy workloads make it difficult to prioritize language practice. ‘This is not good, of course, because words and numbers can decide your fate—they can help you take off and land successfully,’ he concludes.

Author: Olga Sobolevskaya, November 26, 2021