Color vision testing by Farnsworth lantern and ability to identify approach-path signal colors.

INTRODUCTION It is presumed that pilots with abnormal color vision who pass the Farnsworth lantern test can distinguish aviation signal lights including the red and white lights of the Precision Approach Path Indicator (PAPI). The investigation of the FedEx Flight 1478 crash at Tallahassee airport in 2002 raises doubts about this presumption. It found a contributory factor was that the pilot had difficulty distinguishing the PAPI signals because of his deficient color vision (DCV) even though he had passed the Farnsworth lantern. This paper reports on the ability of subjects with DCV who pass the Farnsworth lantern to distinguish PAPI signal colors. METHODS Under a good visibility and a marginal visibility condition, 52 DCV subjects and 52 with normal color vision (NCV) named the colors of simulated PAPI signal lights observed in the dark. Subjects were tested with the Farnsworth lantern and a comprehensive battery of other color vision tests. RESULTS The 10 DCV subjects who passed the Farnsworth lantern made significantly more errors naming PAPI signals than the NCV subjects and 80% made more errors than the worst performing NCV subject. Some confused the red and white signals on more than 10% of occasions. CONCLUSIONS Passing the Farnsworth lantern test does not ensure that DCV pilots can distinguish PAPI signal colors. The criterion for passing the lantern test should be made more stringent. In addition the design of PAPI signals can be improved by a better choice of the white color and by providing a redundant non-color cue. KEYWORDS abnormal color vision, aviation color vision standard, aviation signal lights, color vision tests, PAPI.