Perception in ATC

Perception in ATC


Perception is not merely the process of how information goes through the eyes to the brain, but rather a “set of processes through which we recognize, organize, and make sense of the sensations we receive from the environment” (Sternberg, 2003).

What you see is not necessarily what’s really there. What you hear is not necessarily what’s been said. We get ‘tricked’ by the way the information we receive is processed in our brain. The first stage of Human Information Processing is Perception. This is the stage where the brain decides what it is that has been received. If this decision is incorrect, we have an incorrect image of the world around us. This means that all subsequent Information Processing will be based on an incorrect premise. Processes like Decision Making and following Actions may therefore be wrong as well and it may be obvious that this can easily lead to highly undesired situations in ATM.

Perception and vigilance are closely related and affect the accuracy and currency of our mental model of the air traffic situation. The vigilant ATCO can detect situations where a misperception is likely and will therefore be more likely to detect whether their perception is correct than a non vigilant ATCO.


Misperception can occur in all ATC situations. Here are some examples:

  • A flight is cleared to a heading of 290°. The pilot mishears the clearance and reads back “Flight Level 290”. The ATCO expects to hear back 290 and that is what is heard. For that reason the word “flight level” can easily be missed.
  • A flight is cleared to climb to Flight Level 250. The pilot mishears the clearance and reads back “Flight Level 290”. The pilot may have planned flight level 290 and that’s why they hear 290 instead of 250. Only a slight distraction can be enough to make people hear what they expect to hear instead of what has really been said.
  • A flight is given a climb clearance that is taken by another aircraft on frequency which was expecting a climb clearance. Again it is the expectation which creates the incorrect perception.
  • An ATCO sees an assigned FL 330 in a label and plans the other actions on this perception. Later it turns out that FL350 has always been displayed in the label. Possibly the ATCO perceived FL330 because it suited the plans better.
  • A tower controller does not see the strobe lights of an aircraft on the runway because there are a number of other flashing lights in the same direction due to work in progress.

In all these examples the incorrect perception could easily have led to a dangerous situation if not corrected. If not challenged, it may well lead the controller to a completely incorrect Situational Awareness.

Contributory Factors

Our perception of a situation relies on a combination of different sensory inputs and our existing mental model of the situation. Our senses may be misled by optical illusion or by its auditory counterpart. Perception is strongly influenced by what we expect to see or hear - expectation bias.

Our perception is also dependant on the context from which the specific information stimuli are derived. It has been shown that the same stimuli can mean different things in different environments.

Some equipment displays can give rise to optical illusion (e.g. aircraft trajectory is difficult to interpret, or certain font characters are easy to confuse). In some cases, equipment design has flaws which can make it easier to make a perceptual error and therefore harder to detect and correct it.

Some equipment displays may not allow all operational staff to view them clearly. This is particularly important when angle of sight from some screens does not allow a clear view. Examples include multiple screen displays and/or training/mentoring situations. Sometimes, equipment can be adjusted or modified to take account of design flaws. In other cases, it may be possible to develop simple procedures to reduce the chance of error. However, equipment cannot be improved or safety procedures designed unless the shortcomings of the equipment are brought to the notice of managers. Moreover, if design weaknesses are not notified to the manufacturers, there is a real danger that they may be incorporated in future equipment.


Solutions for Supervisors and Managers

  • Always investigate instances of misperception reported to you by ATCOs. If equipment design appears to be a factor, seek guidance from the manufacturer through the appropriate level of management. Inform other ATCOs on your unit of the problem and discuss, as a team, possible solutions.
  • Always report instances of potential callsign confusion using the appropriate reporting system.
  • Stimulate an atmosphere in which colleagues are willing to take warnings from each other very seriously. It is virtually impossible to detect their own perception errors without input form an outside source.
  • Always take perception errors seriously. These errors are potentially unrecoverable and need special attention to support mitigation.

Solutions involving the Team Members

  • Do discuss any difficulty in interpreting equipment displays with your colleagues and report them to your supervisor or manager. It may be possible to adjust the equipment or develop a procedure to reduce the chance of error.
  • If you are able to think of a remedy to an equipment problem, discuss it with the rest of your team before implementing it as the new procedure may generate more problems. Always inform your supervisor of any new procedure you propose to implement.
  • Always report intermittent faults since these can reduce trust in the information a system displays and transmits.
  • Always use standard phraseology when passing a clearance. In this way, you reduce the chance of the clearance being misunderstood.
  • Listen carefully to read-back and correct any error. When error is detected, insist on a further read-back. Although a routine activity, this activity should not be shared with other tasks, particularly interruptions such as other R/T or phone calls.
  • If, even after a correct read-back, you suspect that a flight has not properly understood a clearance, extra vigilance may prevent a misunderstanding developing into a dangerous situation. Concentrate on this aircraft before doing other tasks.
  • Try to anticipate situations where the wrong aircraft may take a clearance intended for another - like situations with two aircraft with similar callsign on your frequency.
  • Always inform other pilots on frequency of potential callsign confusion and report the matter to your supervisor.
  • Develop sound habits when processing information. One good habit it to ‘Write what you say As You Speak and Read what you hear As You Listen’ - WAYSRAYL. Consult the strips when receiving and annotate the strips during transmission. Record the clearance given.
  • Whenever you suspect that a colleague may have a misperception of a situation or information, insist on pointing this out to the colleague concerned.
  • Do query unclear or incomplete transmissions, especially if you suspect they may have been blocked. This will also indicate to the pilot or other party that they have not been clear and may have an error in their perception.
  • Do use all information available to corroborate your mental picture. Never assume!
  • Use headsets.
  • Use intercom/telephone for coordination.
  • Do not accept phone calls when you are receiving the readback.
  • Always take colleague warnings or advice seriously, almost always they are trying to help you, not question your ability - develop effective TRM practices.
  • Always report error in perception using your local Confidential Reporting system. Unless they are made aware of a problem, it is probable that others will make the same mistake. By reporting through the Confidential Reporting System, you can be sure that the problem will be examined and lessons learned will be passed on to other ATCOs within your unit and in other units with similar tasks.

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