Improved colour vision requirements for flight crew could lead to a 35% increase in the number of prospective pilots meeting the minimum medical threshold.
Colour-blindness research sponsored by the UK's Civil Aviation Authority and the US FAA, and carried out by London City University's Applied Vision Research Centre, has established a more accurate assessment of colour deficiencies in pilot applicants' red-green and yellow-blue colour range.
Under current guidelines applicants with minimal colour deficiencies often fail traditional tests, although vision requirements are open to interpretation and vary between countries.
The CAA says there is no defined limit that specifies the class and severity of colour deficiency beyond which an applicant would not be safe to fly.
Around 8% of males have some form of either red-green or, more rarely, yellow-blue colour deficiency. Fewer than 1% of females are affected because the trait is carried on the X chromosome. This means colour-blindness can be overridden by a second, healthy X chromosome in women, but not by the Y chromosome in men.
ICAO requires flight crew to be able to recognise the primary signal aviation colours of red, green and white, with blue and yellow as supplementary colours.
Colour deficiency was cited by the US National Transportation Safety Board as a possible contributor to a FedEx Boeing 727 landing accident in Florida in July 2002. It stated that the co-pilot might have experienced problems discerning precision-approach lights.
The City University research, which used a colour assessment and diagnosis test, has established the red-green and yellow-blue range more accurately, as well as the class and severity of any deficiency.
"Diversity in colour vision testing methods and standards demonstrates the need to adopt more objective assessment techniques internationally," says CAA chief medical officer Sally Evans.
"If the methods and limits derived from this study were applied as minimum requirements for professional flight crew, 35% of colour-deficient applicants would be eligible for medical certification as a professional pilot."
Evans adds that the CAA will promote the new research internationally with a view to its being accepted in global medical assessments for pilots.