ROLE OF LANGUAGE IN AVIATION SAFETY

 

 

ROLE OF LANGUAGE IN AVIATION SAFETY

INCIDENT-1

The incident happened in April, 2023. The flight was from a satellite base with limited autonomy up to 7000 feet. Above that, the control was with the main airfield situated 30 miles away. On changeover to main airfield at 7000 feet the following interaction took place: -

ATC- “Climb to one zero thousand feet.”

Aircraft- “Climb two one zero thousand feet.”

I announced to the crew that we have been, “cleared to climb twenty-one thousand feet (21000 feet).” Around ten thousand five hundred feet the ATC asked our height and informed that we were cleared only till one zero thousand feet. I retorted that we heard two one thousand feet to which I had made a read back. The ATC negated my claim reiterating that one zero thousand feet was the altitude we were cleared to. He added - “there was a conflicting traffic which has now been given lateral separation and we are cleared for further climb to our cruising level.”

INCIDENT-2

On 19 February 1989, a FedEx-owned Boeing 747, operating as Flying Tiger Flight 66, crashed while flying an international cargo flight from Singapore to Kuala Lumpur, Malaysia. The aircraft was assigned a NDB approach to runway 33 at Sultan Abdul Aziz Shah Airport, Kuala Lumpur. The radio communication was as follows: -

ATC- “Tiger 66, descend two four zero zero. Cleared for NDB approach runway three three.”

Aircraft- “Okay four zero zero.”

The aircraft descended and crashed into a hillside at 600 ft just before reaching the NDB, where minimum descent height was 2400 feet. It hit treetops and burst into flames killing all four crew on board. The ATC had asked the aircraft to descend ‘two four zero zero (2400 feet altitude)’ which was also the minimum descent altitude (MDA). The crew interpreted as descend ‘four zero zero (400 feet altitude)’. The proper radio call from the ATC, instead of “descend two four zero zero”, should have been, “descend and maintain two thousand four hundred feet”. Captain’s read back “okay four zero zero” should have been “Roger, descend and maintain four hundred feet.”

CAUSE-ANALYSIS

 In the first incident the word ‘TO’ was confused with ‘TWO,’ while it reversed (TWO was confused with TO) in the second incident.  To/two are homophones i.e., the words that sound the same, yet have different meanings and at times spelt differently. There are many homophones in English like brake/break, one /won, missed /mist, right/write, Hear/here. Most have little chance of creating confusion in aviation communication except the word for/four of which we need to be careful. There have been, though, many incidents (reported as well as unreported) where words elicited different interpretation/response from listener than intended by the speaker. At round-off the instructor asked the student for take-off power (full power). The student interpreted it as take the power off (remove power) and reduced throttle to zero. For the incident-2 the investigation board blamed the “Non-standard phraseology used by Kuala Lumpur ATC, causing the crew to misinterpret the instructions”. The ATC also failed to detect the incorrect read back by the crew.

Coming back to my flight (incident-1). With the wisdom of hind-sight it was easy for me to see the blunder I made. Even if I interpreted ‘to’ as ‘two’ there were at least two more cues which should have alerted me. The transition altitude for the airfield was 13000 feet and hence the heights above that should have been flight levels and not altitudes.  Also, TWO ONE ZERO THOUSAND amounts to an altitude of more than a lac foot which is absurd. Instead of pondering over the rationale behind ‘two one zero thousand’ I made it ‘two one thousand feet’ almost subconsciously and announced to the crew. What was going on in my mind? Why did I do what I did?  I wish to place the readers right into the circumstances, situation, and context by travelling back in time.

The flight was to a forward area high altitude base. The SOP mandated a climb to 10000 feet overhead in an orbit before setting course to achieve mandatory heights at various check points enroute for adequate clearance from mountainous terrain. It was a hot day and aircraft was heavy. Reaching 7000 feet we changed over to main base and asked for further climb. The reply was, “CLIMB TO ONE ZERO THOUSAND.” It was common to get unrestricted climbs due to nature of commitment. Moreover, we were climbing overhead the satellite base which had no other traffic (as per our knowledge). The temperature at our destination was hovering close to maximum permitted. Any delay would have made us to abort the sortie due to temperature limitations. Inside the cockpit the rate of climb was a concern as we would have barely achieved the mandated heights. Any restriction in our uninterrupted climb would have necessitated one more orbit eating into fuel as well as time. In these circumstances I think I wanted to hear, like most of the times, an unrestricted climb. ATC instructions, “climb to one zero thousand feet” was immediately interpreted by my brain confirming to my expectation (Expectation Bias) i.e., unrestricted climb to two one thousand feet. I distinctly remember reading back, “climb two one zero thousand feet,” which would have been interpreted as, “climb to one zero thousand feet” by ATC, thus satisfactorily completing the process of read back and hear back.

My auditory organs sent the message “climb two one zero thousand feet” to my brain for analysis. The brain uses the schemas already stored of such situations and matches with the context at hand to deliver actionable information which matched with my expectation of being cleared to twenty-one thousand feet. I announced to the crew that we have been cleared to twenty-one thousand feet.

But twenty-one thousand feet could not have been the correct altitude as above 13000 feet (Transition Altitude) should have been in levels. Why couldn’t I register that? Perhaps multiple reasons could have supressed this vital information. Apart from the fixation, expectation bias and the concern to beat the rising temperature, another important factor probably was that the destination base had transition altitude of 24000 feet. Hence, we were used to hearing and repeating figures like two one thousand feet as a result of operating in environments where transition level was high. The entire conversation when we asked for higher climb (at 7000 feet) to the point when ATC checked us for breaching the allotted altitude (at around 10500 feet) would have taken less than a minute in a high work load situation in the cockpit.

SELF-ANALYSIS

The errors committed by me are obvious but needs introspection to understand the tricks the brain can play if we are not hundred percent alive, alert and with the aircraft. It was a humbling experience for me to have revisited all the cognitive biases about which I wrote in the November, 2019 issue of Aerospace safety magazine (Cognitive Biases and communication errors). I primed my brain into expecting uninterrupted climb to cruising level and succumbed to expectation bias to infer ‘climb to one zero thousand’ as ‘climb two one zero thousand’ with emphasis on ‘two one’ which translated into the expected level two one zero.  The figure fed by my auditory senses (climb two one zero thousand) to the brain created a dissonance as it was expecting ‘climb two one zero.’ The brain instantly and subconsciously filled the gaps in conformity with the expectation (Filling in bias). Another safety feature was blocked by authority bias when all crew members accepted my version that we have been cleared to ‘twenty-one thousand feet.’

Few questions, though, remain unanswered. Would we have realized, though belatedly, on our own that above transition altitude (13000 feet) we should have clearance to Flight levels and not like two one thousand feet which indicates ‘altitude’?  Also, could the confusion had been avoided if the controller had called, “climb and maintain one zero thousand feet.” Or be warned of the conflicting traffic, “Climb and maintain one zero thousand feet, reciprocal traffic at one one thousand feet.”?

The ATC controller was alert and had deviated the conflicting traffic laterally in time the moment he noticed us going past 10000 feet on secondary radar. The ICAO Phraseology Reference Guide contains the following to avoid confusion between two and to: - “Use of word ‘to’ directly before a climb/descent instruction or change of heading can be confused as ‘two.’ Such confusion is avoided by using the mandatory words ’flight level’ or ‘heading’ immediately before the numbers.

“Big Jet 345, climb to Flight Level 180”.

“Big Jet 345, turn left to heading 310 degrees”.

THE LISTENING PROCESS

The process of listening consists of multiple stages starting from receiving information through auditory receptors when sound enters the middle ear creating vibrations in tympanic membrane which are passed to the brain through inner ear. Our auditory sensors are constantly exposed to vast amounts of information, but the brain’s capacity to process is limited. To keep the incoming data within its processing capability the brain creates a bottle neck permitting only limited information. This is also expressed as ‘filter theory of attention’ or bottle neck theory. The attention filters of our brain permit only very few bits of information for processing, leaving the rest to be filtered out unassimilated.  Here the incoming data faces another filter called ‘listener’s perceptual filter.’ This filter encompasses listener’s data of lifelong learning and experiences, his mental and physical state, context, environment, and his expectations. The brain also fills up any missing pieces of information based on his experiences. All this happens subconsciously. As an example, when we are talking in a party with loud music and noise in the background people are still able to strike conversation, though very few words are heard. The perceptual filter is the one which turns the message into what we want to hear which may be different than the original message of the speaker.

Some scholars make use of ‘schema theory’ to describe this complex task of decoding and interpreting messages. Schema describes patterns of thinking and behaviour that people use to interpret the world. Schemas are stored in long term memory and are basically built from our life long learnings, memories, and unique experiences. Schemas allow us to take shortcuts in processing and interpreting the vast amount of data fed to our brain. The new information is first run through existing scripts stored as schemas and then interpreted. Schemas also acts as filters and is likely to permit brain to pay attention to things that fit in with their current schemas. It helps to simplify comprehension by comparing new information to existing schemas. However, schemas also distort or alter the new information to make it fit with what they already know thereby distorting the message. 

 

WAY FORWARD

 

Communication breakdown is the leading cause of accidents in aviation. It can happen due to multiple factors like technical issues resulting in equipment failure/partial failure, overriding of messages due RT congestion, static noise etc. It could be due to procedural issues like readback/hear-back error or failure to share information. Cultural factors like power distance, organisational culture and interpersonal relations also play a significant role. All these factors have been recognised and investigated and studied by respective experts. But one factor, language, despite being the most important component of communication is not adequately investigated. The reason being that Linguistics, the scientific study of language and its structure, is not considered one of the many subjects integrated with aviation world. Accident investigators do not have any linguists. Language is not even part of the human factors study.

Language problems arise from the characteristics of the language itself. It has different meaning words sounding exactly alike (homophones). There are words and phrases having more than one meaning.  It has peculiarities of punctuation and intonation which can create confusion in the simplistic situations. Then there are problems with numbers which can be confused with each other. The most commonly confused number which has earned a nick name also is ‘ten eleven issue’. Ten eleven thousand pairing results in maximum altitude bursts. Almost all pilots report difficulty in interpreting messages with several zeroes especially if there are multiple instructions in one transmission. Then there are multiple cognitive biases which tend to change the content as well as meaning of the language based on expectation.  In short, language is complex and need experts (linguists) to unravel its complexity to prevent errors.

Most of the communication errors that take place in aviation are related to inferential nature of the transaction.  ‘Pragmatics’ is a field of linguistics concerned with what a speaker implies and a listener infers based on contributing factors like the situational context, the individuals’ mental states, the preceding dialogue, and other elements. Eastern Air Lines Flight 401 (29 Dec, 1972) could have survived had the crew and the Controller were sharing the same context at a critical time just before the accident. The flight encountered faulty nose gear indication. The entire crew became fixated on the issue ignoring other parameters. The autopilot got inadvertently disconnected and the aircraft got into a shallow descent. The controller, noticing on his radar a decrease in flight altitude flight, radioed, “How are things coming along up there?” in reference to the decreasing altitude. 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 question. The crew, unaware of the altitude problem, was referring to the nose gear problem it had just manged to fix. The controller interpreted OK as referring to the altitude problem. The aircraft soon thereafter crashed. The expectation of the controller and crews had not been aligned.