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Breaking The Stigma: Colour Deficient NOT Colour Blind

Updated: Oct 15, 2023


The Facts

When most people think of the term colour blind they think of the photo above, they believe the person cannot see any colour. This is far from the truth, the condition that causes complete colour vision loss is called Achromatopsia occurring only in approximately 1 person in 33,000, which is extremely rare.


In the majority of cases, people with Colour Vision Deficiency, or CVD will have mild or moderate form. Colour normals otherwise known as normal trichromats, have three cones that perceive different light wavelengths that allow us to perceive colours. However a colour deficient is known as an Anomalous trichromat, meaning that the person has three cone cell types, but one type of cone (the defective cone normally due to hereditary genetics) perceives light slightly out of alignment. The measure of the displacement in alignment determines the severity of the colour deficiency.


There are three different types of anomalous trichromats:

  • Protanomaly, which is a reduced sensitivity to red light

  • Deuteranomaly which is a reduced sensitivity to green light (the most common form of CVD

  • Tritanomaly which is a reduced sensitivity to blue light (extremely rare).



CVD affects approximately 1 in 12 men (8%) and 1 in 200 women. In the UK there are approximately 3 million CVD people (about 4.5% of the entire population), most of whom are male. Worldwide, there are estimated to be about 300 million people with CVD, almost the same number of people as the entire population of the USA!


The stigma is linked heavily to the term 'Blind' which is a very unfortunate label for this condition, and we have to take it upon ourselves to educate our friends, family and most importantly the general public. In addition, what makes it difficult for many to understand CVD or any visual condition, is that no one can see what we can see. Even two colour normals will have different perceptions of colour, colours are only agreed upon by the name we are taught to label them at school, for example, your green will not look the same as someone else's green.


Colour is an illusion which can be better shown than described.....


These balls currently have lines ontop, when the lines are removed what colour are these balls? The answer is at the end of this article.



For more information about how we all perceive colour, Professor Andrew Stockman provides this very interesting Ted talk on exactly that!




Does it affect pilots?

Is the colour actually necessary or is it a secondary aid? Before we look at aviation specifically, let us understand it scientifically and simplistically. The photo below shows a normal photo of fruit in colour.


Now looking at the same photo in black and white below, the Achromatic components. You can still tell what the fruit is, the colour is irrelevant, it is only a secondary aid. The space and detail are contained in this image. This provides us with the most information possible.


But if colour is so important, then let's look at just the chromatic components in the image below. As you can see the chromatic information provides relatively limited information and is far less useful than the black and white (achromatic component).



Now while this example is very simplistic, it also applies exactly the same in flying. As mentioned previously a person's colour vision is normally mild to moderate deficient, unlike the achromatic example which is extremely rare. Therefore it should be the case that there are no activities in aviation flying that CVD pilots with trichromatic vision cannot perform.


Our previous post titled ' Is colour really necessary in the commercial cockpit for safe flight operations?' explains the colour in the cockpit and demonstrates that colour deficient have no problem in both reading and differentiating the colours in this display and there is also evidence to show that even removing colour will have no effects on pilots ability to obtain the critical information needed. (Defence Technology Agency, 2015)


This is reinforced by the fact there have been no accidents ever in the history of civil or aviation related to colour vision deficiency and highlights the industry needs to think more operationally and test pilots using the fairest operational flight tests currently used in Australia , New Zealand and the US, not lab-based test.


The UK CAA argue that the most safety colour critical task in commercial aviation is the identification of the PAPI lights. The Civil Medical Institute of the FAA, who also part-funded the CAA research study into the CAD development but chose not to implement the CAD into the FAA regulations, decided to independently design an operationally more appropriate PAPI simulation task than the one produced by City University London for the UK CAA, which CVD pilots were able to carry out with a high degree of accuracy. (FAA, 2011) The FAA PAPI light test was designed to be a realistic fielded PAPI utilizing actual PAPI lens material and that used the intensity difference of lights. Respondents were asked to identify signals on the PAPI simulator for both incandescent and LED lighting. It was found that when examined using incandescent PAPI, a replica of the PAPI lights used by airfields in the UK, there was no difference in performance between respondents with normal colour vision and those with a colour vision deficiency. Furthermore, the move to an LED technology saw the CVD outperform respondents with normal colour vision and achieve perfect scores in the PAPI light test. (Defence Technology Agency, 2015) (FAA, 2011) (FAA, 2014)


However, the ability of a CVD subject being able to read the PAPI should not be surprising, the lights used in the PAPI are designed such that they will not be confused with one another as they aren’t on the same colour confusion lines. (Defence Technology Agency, 2015) Furthermore, the PAPI lights are rarely relied upon in commercial aviation with the likes of HUD displays and precision approaches for example ILS, making the PAPI lights a secondary aid, not a primary. It is also to be noted that not every airport has PAPI lights and pilots regularly can’t use them in bad weather, for example in CAT 3 conditions.


The stigma that pilots must be colour normal or only have a mild deficiency is completely wrong, pilots such as John O'brien have proven clearly there is no link between the severity of CVD, or the number of colour vision tests you pass, to whether you will be a safe and successful commercial pilot.


The image below shows John Obrien's highly successful career, even though he has failed all CVD lab-based tests.


Conclusion

But let's importantly have a look at what the regulators state regarding the CVD standards.


The European Parliament following Petition No 0528/2018, states that EASA’s position is as follows: “Based on the FAA and ICAO requirements, EASA believes that there are no colour blind pilots (or with severely deficient vision of colours) to an extent that would endanger flight safety, unless they obtained their medical certificate by fraud”, commenting on the US regulatory framework they state operational tests not able to endanger flight safety. (Europarl.europa.eu, 2018)


ICAO the international civil aviation organisation that sets the world's founding laws and regulations in aviation states the following below:

So why is it that regulations are still so restrictive for pilots with CVD worldwide?

Is it because of the stigma....?




The answer to the previous colour vision question.....

Remove the lines, they're all the same colour!

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