Ishihara Plates
The Ishihara plate test is the most common type of color vision test used in aviation. It is given at all first-, second- and third-class medical examinations. The test consists of a plate, with a background color and a two-digit number of another color. For instance, a red background with a green "17." A pilot who can see the number(s) passes the test; while a pilot who cannot is deemed colorblind and fails the color vision test, leading to a deferred or restricted (no night flight) medical certificate.
Farnsworth Lantern Test
The Farnsworth lantern test, or FALANT, was an alternative examination that could be given to pilots who either failed or declined to take the Ishihara plates test. The FALANT consisted of a lantern that flashes light of various colors (including red, green, yellow and white) to a pilot who must discern those colors. According to Leftseat, this test had a higher pass rate than the Ishihara plates. FALANT tests were given at a few locations throughout the United States. As of 2008, the FAA no longer accepts the FALANT as an alternative test.
Flight Test
A pilot who either fails or declines the Ishihara plate test may also apply to the FAA to undergo an in-flight color test. This test takes place during an actual flight, where the pilot takes an FAA medical examiner up on a short flight at an airport with a control tower. The tower flashes light gun signals of various colors (including red, green, yellow and white) at the pilot, who must distinguish the colors.
Failure
Under current FARs, a pilot has the opportunity to pass either the Ishihara plate test or the flight test. If the pilot passes the Ishihara, he must retake the test during every FAA medical examination. If a pilot passes the flight test, he receives a Letter of Endorsement, or LOE, from the FAA exempting him from further color vision testing. If a pilot fails both tests, then he is either denied a medical certificate or issued a restricted medical certificate that does not allow night flight.
Waivers
The FAA may, at its discretion, issue a waiver to a pilot who fails color vision testing. This waiver allows the pilot to be issued an unrestricted medical certificate and exempts her from further testing. It is rare for the FAA to issue a color vision waiver.