Color vision depends on cone receptors in the central, or macula portion of the retina at the back of the eye. The cones contain light-sensitive pigments that allow individuals to recognize color. Each particular cone is sensitive to red, green, blue, or yellow light. Simply put, if the cones lack one or more of these light-sensitive pigments, people may be unable to see one or more of the primary colors.
Medical aviation regulations state that an airman must be able to see aviation colors (red, green, and white). There are a variety of color vision tests that aviation medical examiners use to test color vision for the FAA examination, most commonly Isochromatic Plates, a book containing circles of different colors with embedded numbers.
After an accident in July 2002 when a Boeing 727 landed short of the runway, the NTSB investigation concluded it was due to the pilot's color deficiency and required the FAA to change the color vision test. It is well worth checking out AOPA Foundation President Bruce Landsberg's great article about this accident in AOPA Pilot magazine (“ Safety Pilot Landmark Accidents: Into the Abyss,” September 2007 Volume 50, Number 9).
After the accident, the FAA proposed new testing policies with the intention of identifying more color vision deficient airmen. Pilots know that in the event of radio communication failure one should enter 7600 into the transponder and when landing at a towered airport a signal light gun may be used to indicate permission to land. These guns can show three lights: red, green, and white. Prior to this accident if one could pass the signal light gun test (SLT), an airman could have the color vision restriction removed from his or her medical certificate. If able to pass the SLT, the FAA inspector would issue a waiver for color deficiency—this is now known as a letter of authorization (LOA). The test was the same for all classes of medical certification.
As a result of this accident, the test has been expanded, differs by class of medical, and is now known as the Operational Color Vision Test (OCVT). For third class medicals the test includes the signal light gun plus an evaluation of whether the airman can distinguish objects on an aviation map such as differentiating mountains and lowlands, rivers from grasslands, and so on. Pretty important stuff! For first and second class, one must not only be able to pass the SLT and map reading but also undergo a checkride and identify many things such as different objects on multifunction displays and land topography, be able to perform an emergency landing, and point out lights on buildings, other aircraft, and taxiway lighting.
If one elects to find an eye doctor who has the capability to perform some of the other FAA-approved alternative tests, the person will be required to get the same test done for each subsequent examination he or she has and can no longer obtain a waiver for taking alternative tests. The only way the airman can be free from doing this each time he or she obtains an examination is to take the OCVT and map reading tests, and receive the LOA.
To find out more about these FAA requirements, visit AOPA’s subject report.
For more expert advice and professional assistance with protecting your pilot and medical certificates all year round, visit—and consider joining— AOPA Pilot Protection Services.
This isn't an article about boxing and what happens when you get knocked out, but concerns a hereditary or acquired condition known as color vision deficiency.
Color vision deficiency is the inability to differentiate between certain colors or, in more severe cases, to be able to see colors at all, also known as “color blindness.” Most individuals with color deficiency can see colors, but have difficulty identifying differences between shades of red and green or, less commonly, blue and yellow, and the deficiency varies from mild to severe.