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This Briefing Note (BN) addresses the influence of linguistic factors on communications and how these factors are related to flight safety. 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. Aviation is particularly susceptible to communication issues since higher level English must often be employed to achieve an exchange of ideas related to complex maneuvers or situations.
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. The design and implementation of standard phraseology intended to be used without variation throughout the world can address many but not all language issues. In many circumstances, pilots and/or controllers must resort to the use of higher level English to convey a message. Even when both pilots and controllers speak English fluently, there are pitfalls in the nature of the language and the way that language is heard that can affect safety (Cushing, 1995). Also, within English some words have dual meanings and can easily be misunderstood. This BN will discuss these issues to help flight crewmembers and controllers understand why miscommunications occur and what they can do if problems arise.
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 (Mathews, 2004).
Major studies related to pilot-controller communication errors have been based on the analysis of confidential reports from the Aviation Safety Reporting System (ASRS) database. Grayson and Billings (1981) analyzed more than 5,000 confidential reports and identified 10 categories of pilot-controller communication problems. Two of the categories -- misinterpretation (phonetic similarity) and ambiguous phraseology (more than one meaning) -- are directly related to linguistic issues.
More recently in Europe, Eurocontrol (2005) organized a reporting campaign for European airlines and air navigation service providers. This campaign used a survey of airline pilots and air traffic controllers in Europe to assess communication problems. The survey revealed a large number of reported occurrences of air-ground communication problems in Europe between March, 2004 and April, 2005. Reported problem areas included loss of communication (due to frequency change, sleeping VHF receivers and radio equipment failure) and readback/hearback errors (due to similar call signs, pilot expectations, frequency change). Linguistics (accent, speech rate, ambiguous phraseology) were involved in a great number of these communication problems. Table 1 describes the percentage of certain occurrences associated with errors that were related to linguistic problems.
|Similar call sign||Controller accent (34%), controller speech rate (28%), pilot distraction (22%), pilot expectation (25%) and pilot fatigue (20%)|
|Frequency change||Controller accent (51%), controller speech rate (42%), pilot distraction (43%), pilot fatigue (35%) and pilot workload (31%)|
|Non- standard phraseology||Controller (64%) and pilot (41%) use of non-standard phraseology, controller accent (49%), language problems (46%), ambiguous phraseology (41%)|
|Blocked transmission||Frequency congestion (63%), controller workload (33%), untimely transmission (27%), pilot workload (22%), long message (20%)|
Table 1 : Communications Mishaps Occurrences and Contributing Factors
The percentages listed in Table 1 demonstrate how accents, speech rates, use of non-standard phraseology and general language problems all contribute to errors. These errors have the potential to cascade into larger problems if not corrected by the flight crew or controller.
4 Linguistic factors
This section discusses the underlying linguistic elements affecting controller and flight crew miscommunications. These elements include context and expectations, code switching, English jargon and speech intelligibility.
4.1 Context and expectations (Pragmatics)
Grayson and Billings (1981) found that many pilot-controller misunderstandings can be attributed to 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 prime a pilot to mistake an unrelated communication for the anticipated instruction.
In one real-life example of how expectations can affect safety, prior to a collision a tower controller said, “[airline] [flight number] you are cleared to the Papa Beacon, climb and maintain flight level nine zero, right turn after takeoff,” but the pilot understood “you are cleared to take off.” The controller intended the instruction to pertain to a takeoff clearance still to come, but the pilot was expecting a clearance and thought the instructions were to be acted upon immediately. This misunderstanding led to a collision with another aircraft.
Pragmatics is a branch of linguistics concerned with bridging the gap between a speaker’s intended meaning for a phrase and the phrase’s meaning to the hearer. For Grice (1989), the crucial feature of pragmatic interpretation is its inferential nature. The hearer is seen as constructing and evaluating a hypothesis about the speaker’s meaning based on the meaning of the sentence uttered and on background or contextual assumptions and general communicative principles that speakers are normally expected to observe. Context here is the situation since it may include social, environmental and psychological factors.
Although speaking a common language is essential, pilots and controllers must also share the same context. One example of the impact of having different contexts occurred when a controller, noticing on his radar a decrease in altitude for a flight, radioed the flight crew, “How are things coming along up there?” in reference to the decreasing altitude. However, the crew had been preoccupied with a nose gear problem and had informed several controllers, but not the current one, about the issue during their flight. The crew responded “OK” to the controller’s questions. The crew, unaware of the altitude problems, was referring to the nose gear problem it had just managed to fix. The controller interpreted OK as referring to the altitude problem. The aircraft subsequently crashed.
In each of these examples, the accidents may have been avoided if the expectations of the controllers and crews had been more aligned.
4.2 Code switching
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 often occurs in bilingual communities or families. Sometimes the switch lasts only for a few sentences or for a single phrase. Code switching within a sentence tends to occur more often at points at which the syntaxes of the two languages align. Thus it is uncommon to switch from English to French after an adjective and before a noun because a French noun is normally followed by its adjective and English is just the opposite. Code-switching between a subject and its verb is much more likely because both English and French normally place the subject before the verb.
Code switching can occur even between native English speakers and often involves switching between technical jargon and vernacular English (normal spoken language). This can lead to problems when the same word has different meanings in the technical and vernacular language. In one particular accident, a flight was cleared to land at the same time another flight was cleared to taxi into position for takeoff. The controller told the in-air flight to go around, but the captain asked for the permission to continue landing and inadvertently used the word “hold” to express his request while speaking to his first officer. Specifically, the pilot said “can we hold? Ask him if we can hold.” In aviation jargon, “hold” always means to “stop what you are doing,” but in ordinary English it means to continue on the same course. The controller agreed for the flight to “hold” intending for it to go around, but the flight continued with the landing and collided with the aircraft on the ground.
4.3 Speech intelligibility
The ICAO language proficiency requirements apply to native and non-native speakers alike. The intelligibility of non-native speakers depends on the extent to which their languages share phonological and grammatical features with English. There are many instances where distinct sounds in one language are interpreted as being the same by foreigners. For example Japanese speakers have difficulty detecting the difference between “R” and “L” sounds in English, and Dutch and Spanish speakers have trouble differentiating “S” and “SH.” Native speakers of these languages must make a special effort to learn to differentiate between these sounds (Fry, 1977). Therefore, according to ICAO, native English speakers must familiarize themselves with the dangers of cross-cultural communications (Mathews, 2004). All parties must make a concerted effort to know the potential issues that can arise related to speech intelligibility.
4.4 Paralinguistic factors
Paralinguistic factors include voice intonation, stress, rate of delivery and pause/hesitation. According to Shames & Wigg (1990), paralinguistic factors can change the form and the meaning of sentences by acting across individual sounds or words of a sentence. In one particular instance that led to an accident, ATC did not perceive the severity of a flight’s fuel crisis because controllers did not perceive a change in stress or pitch in communications with the crew (Fegyveresi, 1997). In turn, ATC did not give high priority to the situation, and the aircraft crashed.
Another problem area in aviation arises from excessive pausing during radio transmissions. When someone pauses for a long time during a transmission but does not release the radio talk button, incoming communications are masked. Also, an excessive pause can invite another person to begin a transmission that will “step on” or mask the original transmitter’s communications.
When under stress or in complex situations, speech becomes more rapid and frequent and can make communications very difficult to understand. Under these stressful conditions, changes in voice pitch can cause “slips of the tongue” that can lead to misunderstandings and errors (Prinzo & Britton 1993, Timolin & Pikovski, 1974; Fegyveresi, 1997).
4.5 Aviation jargon leads to ambiguity
In the United States, more than 300 runway incursions occur annually (R.K. Jones, 2003). Such a large number of runway incursions indicates that even native English speaking pilots are having trouble communicating with native English speaking controllers. Aviation jargon is one of the biggest contributors to runway incursions because of its complexity and often overlapping or ambiguous use of numbers.
The numbers used in pilot-controller communications are used to indicate multiple aviation parameters (e.g., flight level, heading, air speed, airline flight number). The overlapping number ranges can leads to misunderstandings, especially in high workload or time-pressured situations. A common mistake occurs when changing heading or flight level. For example, when an aircraft is flying on a heading of 300 degrees at FL 270 the controller vectors the aircraft to “three one zero”; the pilot acknowledges “three one zero” and climbs to FL310 instead of turning to a course of 310 degrees. The pilot simply interpreted the request for a heading change as a flight level change command.
This issue is more prevalent when an ATC message includes two or more sets of numbers that apply to separate actions. In the recent Eurocontrol survey, it was found that pilots and controllers think that a frequency change is often wrong when it is a part of a long message. It is recommended that the number of instructions per call be limited and that a frequency change be issued by itself.
In most instances a full readback would eliminate problems related to jargon ambiguity. Such readbacks are essential to the confirmation/correction loop, which allows all parties involved to check the correctness of the information that is being communicated.
4.6 Homophones, homographs, homonyms and synonyms
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 (sewer, a conduit for waste vs. sewer, a person who sews). 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). The word homonym, however, is often used to refer to both homophones and homographs.
An example of a communication error involving a homophone is: ATC cleared an aircraft for descent to “two four zero zero”. The pilot read back, “ok. Four zero zero.” The aircraft then descended to 400 feet instead of 2400 feet. The pilot mistook the number “two” to mean “to” and descended accordingly.
Table 2 contains some common aviation homophones and homographs. Table 3 contains some common aviation homonyms.
Table 2. Homophones (same sound) and homographs (same spelling)
|Brake / Break
One / Won
Two / To
Missed / Mist
Right / Write
Hear / Here
|Content (accept) / Content (things inside)
Refuse (disagree) / Refuse (rubbish)
Close (shut) / Close (near)
Right (direction) / Right (correct)
Table 3 . Homonyms (same sound and spelling but different meaning)
|Taxi||Helicopter (hover taxi, air taxi) / To move|
|Aircraft||One or many aircraft|
|Flight||Apparatus / Persons|
|November||Name of letter N / Aircraft identification letter / Month|
|Tango||Name of letter T / Air taxi or Helicopter|
|Zulu||Name of letter Z / Time at Greenwich meridian|
|Contact approach||Type of approach to an airport / Command to radio the controller who handles approaches|
|Gate||Location at the terminal building / Point in the sky|
|Roll||Pivot in the air about longitudinal axis / Forward movement|
|Slot||A part of forward edge of some wings / Time interval for a takeoff|
|Remain||Localization / Radio frequencies|
|Flight deck||Top of an aircraft carrier / Cockpit of an airplane|
|Go ahead||Urge speaking / Forward motion|
|Stand by||Wait / standing|
Synonyms are words or phrases that sound different and are spelled differently but have the same meaning. There are 49 instances where the Federal Aviation Administraton (FAA) and ICAO use different words for the same meaning. Some common aviation synonyms are listed in Table 4.
Table 4. Synonyms: Multiple FAA expressions for a single meaning
|Fly around the airport||Circle the airport / Circle the runway / Go around|
|Turn around on the runway and travel toward the arrival end of the runway||Taxi back / Back taxi|
|To check information already given||Say / Verify / Confirm|
|For instant action||Immediately / Expedite / Without delay|
|Tell your speed||Say speed / Say Mach number|
|Signaling emergency||Mayday / Pan-pan|
|Balloon in the area||Derelict balloon / Unmanned balloon over|
|Paved area near the runway||Ramp / Apron / Tarmac|
|Time||Greenwich Mean Time / Zulu / UTC|
|Severe danger due to wind||Wind shear alert
Wind shear/microburst alert
Departure Wind shear/microburst alert
Low level Wind shear advisories in effect
Multiple Wind shear/ Microburst alert
Possible Wind shear outside the system
|Desisting from an action||Hold (FAA) / Stop (ICAO)|
|Moving away from something||Exit (FAA) / Vacate (ICAO)|
The above examples are taken from “The Pilot’s Reference to ATC Procedures and Phraseology” referenced by Jones (2003).
5 Key points
6 Additional OGHFA Materials
7 References and Addition Reading Material
Fry, Dennis.: Homo Loquens: Man as a talking animal. Cambridge University Press: Cambridge, London, New York, Melbourne, 1977
Grice, H. P. (1989) Studies in the Way of Words, Cambridge, MA.
EUROCONTROL.- Air-Ground Communication Safety Study. Causes and Recommendations.
FEGYVERESI (A.E.).- Vocal cues and pilot / ATC Communications. In: Proceedings of the Ninth International Symposium on Aviation Psychology, April 27-May 1, 1997, Edited by R.S. Jensen and L.A. Rakovan, Volume 1, pp. 81-84.
GRAYSON (R.L.) ; BILLINGS (C.E.).- Information transfer between air traffic control and aircraft: Communication problems in flight operations.- In: Information Transfer Problems in the Aviation System. / C.E. Billings ed. ; Cheaney ed.- NASA Technical Paper 1875, National Aeronautics and Space Administration, 1981.
JONES (R.K.).- Miscommunication between pilots and air traffic control.- Language Problems & Language Planning, vol. 27, n° 3, 2003, pp. 233-248.
MATHEWS (E.).- New provisions for English language proficiency are expected to improve aviation safety.- ICAO Journal, vol. 59, 2004, pp. 4-6.
MONAN (B.).- Readback Hearback.- ASRS Directline, 1991, n° 1.
PRINZO (O.V.) ; BRITTON (T.W.).- ATC / Pilot Voice Communications - A Survey of the Literature.- Federal Aviation Administration Report DOT/FAA/AM-93/20, November 1993.
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