Seeing is believing


Should we believe everything we see?

A few days ago I unintentionally turned off all power to the aircraft. Not a big deal you might think and, in this particular case, it wasn’t. We had just parked up outside the terminal at Brussels and were completing the post-flight administration whilst our 300 or so passengers were slowly making their way off the aircraft. The ground personnel informed us that the aircraft had been connected to the airports ground power supply and that we should shut down our Auxiliary Power Unit (APU) - a small jet engine in the tail that provides air and electrical power to the aircraft when the engines are not running. I reached up to the overhead panel and selected the primary and secondary external power sources then switched off the APU…. a few seconds later the entire aircraft powered down. 

As it transpired we had already selected the external power switches and I then turned them back off! Had this happened just prior to departure I would have likely caused a 20-30 minute delay which would definitely have led to some incredibly disgruntled passengers, potential reputational damage and in the most extreme case a financial penalty. 

Once the embarrassment had worn off and the crew had cycled through the flight deck to enjoy a few laughs at my expense I was able to reflect on what had happened in that moment. I remember looking at the switch lights and seeing them say ‘on’ indicating that the external power source was connected and in use however, I had not made the selection and the indication made no sense. This did cause me to pause momentarily but ultimately I pressed the switch again, de-selecting the external power source thereby changing the caption to ‘available’. I was expecting to have to press the switches and to see both ‘on’ and ‘available’ captions during the process. 

We [human beings] are very skilled at seeking evidence which confirms our expectations and ignoring/avoiding evidence which refutes it; we actively try to make the world fit the image we expect to see - we look for things that support our hypothesis or ideas that the image we are seeing is correct. You see this often when teaching people to use a map and compass. Instead of looking around them for obvious features and clues in the environment to assist with locating their position they instead work the other way. They look at where they believe themselves to be and ‘force’ the features they should be seeing onto the environment in an attempt to convince themselves of their location. 

The human tendency towards confirmation bias strengthens expectance effects making it harder to break the chain and see what is really there. Another compounding factor is the way in which our brains focus attention on the tasks at hand – it can only focus on one task at a time. If we introduce a secondary task, in this case switching aircraft power systems, we can easily overload the system. Interestingly several of my colleagues have also made the exact same error under very similar circumstances. 


In this case I was distracted by other activities and despite seeing all the required information I failed to fully understand what I was seeing – I hadn’t given my brain time to process all the information. Had I briefly paused my other activities to focus entirely on this new task it may have provided me with the additional spare mental capacity required to understand what the aircraft was telling me. This would have enabled me to adjust my actions rather than just employ the normal sequence of events.

Whilst the consequences for me were minimal, under different circumstances, they could have been significantly worse. Several years ago I was cycling through a town near me during the daytime and wearing high visibility clothing when the driver of a car pulled out in front of me nearly knocking me from my bike. I remember making eye contact with the driver but he just didn’t see me – he wasn’t expecting me to be there. How many times have you looked but not seen or has something in your periphery grabbed your attention at the last minute meaning you manage to avoid an accident/incident (just)?


If we are aware of our limitations and where we are likely to make errors we can employ methods to [hopefully] counteract them or at least be more aware of where they may occur. As [car] drivers we are very good at spotting other cars when at a junction but much less adept at spotting motorbikes/pushbikes – there are fewer on the road and so we see them much less often. The ‘Think Bike’ campaign that can be seen on many country roads in the UK is designed to make drivers expect to see a bike on the road. By expecting to see a bike when checking the road is clear at a junction we are more likely pause, look properly and then see what is actually there.

Seeing, it seems, isn’t always believing.