Primarily for general aviation discussion, but other aviation topics are also welcome.
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By Rob P
During my flying career I have always been short sighted (Physically, not in terms of forward thinking) and have been allowed to fly through having devices such as contact lenses or spectacles that have enabled me to meet a laid-down standard.

Also in this time I developed a colour deficiency that meant I now failed the Ishihara test and had my previously held night qualification suspended and 'flight by day only' in big, friendly letters on my Class 2.

But I do know that with a slightly pink tinted lens in front of the eye it is possible for me to sail through the plates without difficulty.

I wonder therefore why, if wearing rose-tinted glasses, I shouldn't be legal to fly at night, just as by wearing corrective lenses I can fly by day?

Rob P

Theoretical, as I fly an aircraft that is even now not fully equipped to fly at night and from a base airfield without lighting.
The CAA say.. in

"Lenses to alter colour perception – these are coloured lenses which filter specific wavelength bands and are occasionally worn by people with colour vision deficiencies to aid them in a particular area where they may confuse certain colours. The lenses do not correct a colour vision deficiency but merely move the colour confusion to a different area of the colour spectrum. They are not compatible with aviation use."

I will say that in my career as an AME, (now retired) I came across a few people who had passed an initial PPL colour vision test (either Ishihara or lantern test of various flavours), then subsequently failed a second Ishihara (usually at an initial Class 1 where the test was performed under more stringent and standardised control). Most of these went on to pass the then new CAA computerised CAD test.
Rob P liked this
Thank you. Every day is a school day.

As you can probably gather, it isn't a major factor in my flying life. Even when I held the qualification it was rarely used other than to revalidate at the start of the winter. It's a great qualification / rating to earn, and there were some beautiful nights I recall, but of practical use for my sort of flying? Negligible.

Rob P
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According to the Air League, there is no real need for any colour vision defective pilots to be restricted to day only. ... lation.pdf

It’s a very interesting read. The CAA themselves state that the PAPIs are the only critical task, so this phrase jumped out from the report:-

“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”

I have flown many hundreds of day time approaches to PAPI equipped runways and I have always been able to read and interpret the signals at least as well as my “normal” students. Judging by the few night flights that I have done as a passenger, the PAPIs are far easier to interpret at night.
Having been colour deficient from an early age, it's the reason that aviation didn't become a career for me. It wasn't until years later I found I could have a PPL. When I did my medical for that I knew I would fail the Ishihara tests (though at one point while at school I was being tested so regularly that I'd memorised them and could actually pass them if I saw which number book they took off the shelf) and so I ended up doing the Giles Archer lantern test at the CAA Gatwich, which I passed. I now have on my record that my colour vision is sufficient not to bar me from any flying operations.
PeteSpencer liked this
Can the level of colour deficiency change over time? Either get worse or less of a deficiency?
I too found I was colour deficient all those years ago so had required stamps on my medical cert.

I also just fell below the required standard when taking the colour lantern test (RAF Institute of Aviation Medicine - London), so that was the end of my potential career as a NATS assistant air traffic controller!
It can definitely get worse

That's why I am now "day only" whereas before I held a night qualifica

Rob P
I passed the Ishihara test on my first ever Class 2 and have never been tested since. I once asked why and was told by the AME that colour vision doesn't deteriorate.

Banning someone from commercial/night flying because they *might* have trouble with a PAPI (but not even testing it explicitly) sounds just like the sort of overbearing thing our beloved CAA would do.
@Rob P

My understanding of the Ishihara test is that it is an initial screening test for colour vision, if not passed you should be offered a lantern test to determine more accurately what areas of your colour deficiency are, red/green, red/white, green/white etc.


It is an accepted screening test for red/green colour vision deficiency. (the vast majority of colour vision deficient people are red/green and blokes)

UK CAA has determined that the only acceptable follow up test is the CAD test as developed by them together with City University London.

The congenital colour deficiency does not change over life. It is baked in your genes. That genetic relation is also the reason why it is mainly blokes that are affected.

Other regulators use other follow up tests for those who fail the Ishihara plates. From a variety of lantern tests to just looking at the light guns at a tower in a variety of ambient stages of darkness (the FAA)

A lot has been written in both scientific literature and the internet.

The conclusion from that has to be that 1) there are differences of opinion and 2) the role of colour vision in the safe discharge of aeronautical duties is not as significant as many traditionally have believed.

There is good empirical evidence for that as well - those who are of a different opinion should maybe read 'We landed by moonlight' Night time landings in Lysanders and associated stuff in occupied Europe with the sole benefit of guidance some 1940s lanterns - no PAPI in sight.

Also on offer is an acquired colour vision issue, certain eye conditions (some as common as the development of cataracts - everyone over the tender age of 40 has that to some degree) and medication (quinine to name but one) can cause a shift of colour vision discrimination ability.

A good one to remember is that certain medications from the resurrection department can give a temporary colour vision problem; hence the need to abstain from flying within 36 hours of taking Viagra.

As a medical assessor I was once challenged about that by a professor in urology. My invitation to send me the evidence has to date not received a reply......
cjrpaterson, Dodo, PeteSpencer and 1 others liked this
cjrpaterson wrote:The only other reason I can think of is recognising port/starboard nav. lights?

I might have little or no difficulty recognising them.

But I am b*gg*r*d if I can remember which is which.

Rob P
Rob P wrote:But I am b*gg*r*d if I can remember which is which.

My mnemonic is that the longer/shorter words all go together:
Red / Port / Left
Green / Starboard / Right

Well, it worked for me!
Rob P liked this