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A pilot is flying IFR through a layer of clouds with supercooled droplets. The heating element of his/her static port is inoperable because of a broken wire. The static port eventually ices over, freezing his/her altitude and vertical speed indications. A thin layer of ice also builds up on the windscreen wiper. When his/her aircraft hits slight turbulence, the pilot experiences a feeling of entering a shallow descent. Moments later, pressure builds up in his/her ears which can be cleared by swallowing. His/her engine appears to have become a little louder, which he/she attributes to the hearing loss associated with blocked ears. Only when he reaches the cloud base does he/she realise that he/she is indeed in a descent. Why didn’t the pilot detect the deviation before?

  • A
    Because well-trained pilots consider external data from all channels equally, the receipt of a bad piece of information makes it impossible for him to exclude the false data from his mental model.
  • B
    People tend to give most weight to information received visually. Once they have made up a mental picture, there is a tendency to ignore data which contradict that picture.
  • C
    The pilot has received insufficient training in instrument flight, which is why he is unable to maintain situational awareness when he loses outside reference.
  • D
    The pilot seems to have a problem with pressure equalisation, which makes it impossible for him to detect that his aircraft has entered a descent.

A mental model is an explanation of how something works. We generate a mental model on the basis of past experience and learning. Our mental models help shape our behaviour and define our approach to solving problems and carrying out tasks. An inherent danger in this system is that, having built a mental model, we will tend to seek only information that confirms our model (confirmation bias) and ignore other information that may cast doubt on its accuracy.

When flying in IMC through clouds, the pilot is unable to see his/her surroundings, and the only source of visual data are the flight instruments. However, in this case, his/her instruments are receiving erraneous data due to the blocked static port. Remember that presentations using visual aids are said to be 43% more persuasive than unaided presentations. Therefore, even if the pilot is receiving other hints that the aircraft is descending, he/she is unable to overcome his/her wrong mental model.

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