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English is the official language of aviation. Today, English is spoken by more non-native speakers than native speakers. Many flight crews are now composed of non-native English speaking pilots from different countries. This situation, combined with the fact that many controllers are non-native speakers, can lead to substantial communication issues that can affect flight safety. Therefore, any discussion of communications must focus not only on the intelligibility of non-native speakers to native speakers but also on the interaction between non-native speakers. Effective communications within crews and between crewmembers and controllers are essential for safe air travel.

Linguistic problems can arise any time people are communicating and are especially a problem when one or more of them is not a native speaker of the language being used. According to the International Civil Aviation Organization (ICAO), between 1976 and 2000, more than 1,100 passengers and crew lost their lives in accidents where language issues played a contributory role.

Many pilot-controller misunderstandings can be connected with expectations that lead the listener to hear what he or she was expecting to hear instead of what was actually said. The expectation of a particular instruction can force a pilot to make a mistake in an unrelated communication for the anticipated instruction.

Code switching is a term that refers to the alternation between two or more languages, dialects or language registers in the course of communications between people who have more than one language in common. Code switching can occur even between native English speakers and often involves switching between technical jargon and normal spoken language.

Some pilot-controller communication errors arise when words sound or look alike but have different meanings. Such words are called homophones, homographs or homonyms. Homophones are words that sound alike but have different meanings and may or may not be spelled the same way (to vs. two). Homographs are words that are spelled the same way, but have different meanings and may or may not be pronounced differently (live – as a verb vs. live – as an adj / adv). In the strictest sense, a homonym is both a homophone and a homograph. That is, true homonyms are spelled the same and sound the same, but have different meanings (bear may refer to the animal, or to a movement in a certain direction).

Paralinguistic factors include voice intonation, stress, rate of delivery and pause / hesitation. Paralinguistic factors can change the form and the meaning of sentences by acting across individual sounds or words of a sentence. Another problem area in aviation arises from excessive pausing during radio transmissions.

Absent-minded slip is a form of miscommunication which controllers and pilots will make occasionally. Such slips are usually associated with an internal preoccupation or external distraction. They are a problem of experts, not of beginners because experts more often than not perform at an automatic, subconscious level (e. g. - a controller may routinely assign the same level for descent to arriving aircraft. But on one occasion that conflicting traffic at that level has been noted, the controller may still absent-mindedly assign that level to an inbound aircraft instead of providing level separation).

Ambiguity is a form of miscommunication which arises from the presence in a word or phrase of more than one possible meaning or interpretation(e. g. - Words with uncertain reference, such as the pronouns “him” or “it” or indefinite nouns such as “things”, may be ambiguous and can cause confusion, as we saw in the Florida Everglades crash in 1972).

The use of similar call signs by aircraft operating in the same area and especially on the same RTF frequency often gives rise to potential and actual flight safety incidents. This hazard is usually referred to as “ call sign confusion ” (e. g. - Call signs coincidentally contain the same alphanumeric characters in a different order (e. g. – AB 1234 and BA 2314)).

Read-back is defined as a procedure when the receiving station repeats a received message to the transmitting station so as to obtain confirmation of correct reception. An uncorrected erroneous read-back (known as a hear-back error) may lead to a deviation from the intended clearance and may not be detected until the controller observes the deviation on his / her radar display (e. g. -  numerical errors, such as confusing “one zero thousand” with “one one thousand”).