Originally Posted by
aterpster
RA50 is an Alert Height. Fail operational CAT III does not have a DA.
This is not completely correct although it may be mostly correct.
Here is part of the FAA/JAA definition for CAT IIIB which is fail-operational. "A category III B approach is a precision approach and landing with no decision height or a decision height lower than 50ft (15m)...."
In other words, sometimes there is a decision height. For example, I have seen in our company limitation for Paris, a DH of 14 feet. Pretty low.
I suspect that the original poster is flying a 777 and the Alert Height is more likely around 200 feet. The 50 RA on the 10-9S chart for YYZ is the new minimum according the new revised rules of the bureaucrats in the EU for operators following their rules. What is the reason? Maybe it has something to do with lighting but I don't know.
Mind you, the original question was about a CAT IIIA approach. Perhaps his normal company minimums based on that particular country's approval for this Fail-Passive approach is 50 RA anyways(unless stated as higher in the Jepps). It is at my company.