The use of language for verbal communications adds the dimension of pronunciation within any language because of regional differences in speech dialect. There are also the issues which arise from variations in English language proficiency amongst the many who must use it for radio communications in respect of international air transport but who do not have it as their first language. These users can reasonably be expected to have a wide range of proficiencies in the use of it.

Abbreviated English

Use of Standard Aviation English phraseology is a major contribution to the reduction of ambiguity in Aircraft/ATC exchanges and supports a common understanding among speakers of both:

  • different native languages and
  • the same native language, but who use, pronounce or understand words differently.

Plain Language Communications

Whilst Standard phraseology is at the core of effective verbal communication, it is recognised that circumstances where plain-language communications in English become necessary. Difficulties in plain language communications between ATC and Flight Crew have often helped to cause serious incidents and accidents or made the response to such circumstances arising from un-related causes more difficult. It is in recognition of this that ICAO has introduced a language proficiency system. However, this does not seek to address the considerable differences in accent which exist between confident speakers of English, whether it is their first or other language. These differences can also add to the task of a less confident english language speaker when seeking to understand those with a more extensive language ability.

Structuring ATC Communications

For all ATC / Flight Crew communications, the first priority is to establish an 'operational context' that distinguishes the following elements:

  • Purpose - clearance, instruction, statement or proposal, question or request, confirmation;
  • When - immediately, anticipate, expect;
  • What and How - altitude (climb, descend, maintain), heading (left, right), airspeed; and,
  • Where - (at […] waypoint).

The content of initial and subsequent messages should support this 'operational context' by:

  • Following the chronological order of the actions;
  • Grouping instructions and numbers related to each action; and,
  • Limiting the number of instructions in the transmission.

The last point is of great importance, especially now that RTF frequencies have up to three decimal places, which has significantly added to the potential complexity of multiple insruction tranmissions and their correct recording and read back by flight crew.

The intonation, the speed of speaking and the placement and duration of pauses may affect the understanding of any communication, whether in abbreviated or plain language.

Communication between Flight Crew members

CRM studies and investigations into many accidents and serious incidents have shown that language differences on the flight deck can sometimes be a greater obstacle to safety than the associated cultural differences. However, cultural differences can also be the cause of misunderstandings about the meaning of the language used even when all crew are able to speak English in an apparently competent manner. This possibility may be heightened where cultural emphasis leads to a belief than understanding exists when it has not been achieved. Such circumstances can be aggravated in the presence of a strongly authoritarian culture.

In many parts of the world, language differences generate an additional communication issue which can affect safety performance when controllers use English to communicate with international flights and their local language to communicate with flights by locally-based operators. This can prevent some of all visiting flight crew from achieving a proper level of situational awareness in respect of other traffic.

Accidents and Incidents

The following list contains occurrences where language issues are considered a contributory factor.

On 12 November 1996, an Ilyushin IL76TD and an opposite direction Boeing 747-100 collided head on at the same level in controlled airspace resulting in the destruction of both aircraft and the loss of 349 lives. The Investigation concluded that the IL76 had descended one thousand feet below its cleared level after its crew had interpreted ATC advice of opposite direction traffic one thousand feet below as the reason to remain at FL150 as re-clearance to descend to this lower level. Fifteen Safety Recommendations relating to English language proficiency, crew resource management, collision avoidance systems and ATC procedures were made.

On 5 April 2019, a Boeing 737-500 crew declared an emergency shortly after departing Madrid Barajas after problems maintaining normal lateral, vertical or airspeed control of their aircraft in IMC. After two failed attempts at ILS approaches in unexceptional weather conditions, the flight was successfully landed at a nearby military airbase. The Investigation found that a malfunction which probably prevented use of the Captain’s autopilot found before departure was not documented until after the flight but could not find a technical explanation for inability to control the aircraft manually given that dispatch without either autopilot working is permitted.

Whilst a light aircraft was lined up for departure, a vehicle made an incorrect assumption about the nature of an ambiguously-phrased ATC TWR instruction and proceeded to enter the same runway. There was no actual risk of conflict since, although LVP were still in force after earlier fog, the TWR controller was able to see the vehicle incursion and therefore withhold the imminent take off clearance. The subsequent Investigation noted that it was imperative that clearance read backs about which there is doubt are not made speculatively in the expectation that they will elicit confirmation or correction.

On 3 August 2017, a Boeing 737-900ER landing at Medan was in wing-to-wing collision as it touched down with an ATR 72-500 which had entered the same runway to depart at an intermediate point. Substantial damage was caused but both aircraft could be taxied clear. The Investigation concluded that the ATR 72 had entered the runway at an opposite direction without clearance after its incomplete readback had gone unchallenged by ATC. Controllers appeared not to have realised that a collision had occurred despite warnings of runway debris and the runway was not closed until other aircraft also reported debris.

On 21 September 2012, two aircraft came into conflict in Class 'A' airspace whilst under radar control at night and loss of separation was resolved by TCAS RA responses by both aircraft. Investigation found that one of the aircraft had passed a procedurally-documented clearance limit without ATC clearance or intervention and that situational awareness of its crew had been diminished by communications with the conflicting aircraft being conducted in Spanish rather than English. A Safety Recommendation on resolving the persistent problem of such language issues was made, noting that a similar recommendation had been made 11 years earlier.

Related Articles

Further Reading

AGC Safety Letters:

EUROCONTROL Action Plan for Air-Ground Communications Safety:

EUROCONTROL Level Bust Toolkit:


SKYbrary Partners:

Safety knowledge contributed by: