Following Clinton's brilliant post, I thought I'd inform the debate further with the following links"
Clark and Gordon Hazards of Colour Coding in Visual Approach Slope Indicators
This link is to a document, published by the Australian Defence Research Laboratories, which very clearly describes the inherent risks of contamination of the PAPI code, based on red/white discrimination, resulting in the distortion of the signal and ultimately, when it fails, it fails "UNSAFE".
When you've read this, and compared it with the NTSB report, it will be manifestlyclear that the crash was entirely due to a "fail unsafe" scenario with the Tallahassee RWY 9 PAPI.
The second link is to a paper, co-authored by myself and Boris Crassini, analyzing the dilemma inherent in the crash investigation, and proposing an alternative explanation (to that reached by the NTSB) of the crash.
The Puzzle of the Crash of Fedex Flight 1478: Implications for Colour Vision Standards in Aviation
:Thank you Clinton for bringing on this discussion.
Do note that the Clark and Gordon document does predict that CVD pilots may have difficulties identifying the PAPI code in certain circumstances, a conclusion I don't have any problem accepting.
To me the Fedex crash circumstances were a perfect fit for the predictions made by Clark and Gordon