The extent to which the NTSB went to try to refute any potential problem with the particular PAPI during the particular approach in the particular conditions, is very puzzling to me. The objective evidence of the patent defect in PAPI had been around for decades. This, too, from the NACTA submission to the NSTB:
Testing of the same brand and model of PAPI lights by Transport Canada, as per Aerodrome Safety Circular No. 98~002 (Attachment #3) revealed that:
- Contaminants such as ice, dew or frost on the PAPI front lens surface does affect the projected signal.
- the testing concluded that false slope indication produced as a result of contamination on the lens is a design problem.
That's why the manufacturer's instructions included that: "The PAPI system must operate continuously when the runway is in service." The Tallahassee PAPI was instead linked to the PAL. The pilots activated the PAL mere minutes before arrival.
The aircraft was on approach near dawn when the temperature and dew point were the same and the PAPI had only been activated for minutes. Yet the NSTB report makes a conclusive statement as to what the PAPI was indicating at the time.
I have to say it, because I see it so often in relation to pilot CVD: I believe the NTSB's conclusive statement to be intellectually dishonest.