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wongben4

CAT IIIc for 744

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Guest D17S

As far as airplane landing performance, there is no difference between Cat 3b and Cat 3c. In either case, the airplane is committed to autoland. In a cat 3b ©, there is no "Decision Height" -- that would imply that the pilot has a choice to "Go Around." There is no Decision to made at a specified Height about the wisdom of continuing the autoland maneuver. Cat 3b © have only an "Alert Height" -- meaning "Wake up. Here it comes!" Very simply, at Cat 3b runway visibility limits, the airplane is committed to land . . . or touch-down on something anyway. The wheels are going to touch dirt or concrete or "land" of some sort. It's simply too late for the pilot to do anything about it. The airplane is landing. Cat 3c is generally considered an airplane limitation but really, it is not. It is an airport operational limitation. Cat 3c would get the airplane stopped on the runway OK. Cat 3b does that already. So what's the deal with 3c? Here's the problem: 3c visibility does not provide enough visibility for the airplane to taxi off the runway. Cat 3c strands the airplane on the runway. Consider this: The first airplane that lands Cat 3c shuts down that runway until visibility improves to cat 3b. Parallel runways? Two side by side Cat 3c landings and the airport is shut down. The 'follow-me' truck can see better than the airplane? How does that work? Even the truck stranded! So operationally, Cat 3c doesn't work for the airport. The airplane would be just fine with it. But Cat 3c would require a zero-zero 'taxi to the gate' system as well as an tight, stable ILS. GPS will allow this with Lnav type systems in the future, but right now I haven't heard of any 3c taxi systems. It would need an airport and airplane with matching technologies. Didn't Amsterdam try burying a steel cable along the way years ago? Airplane had a 'cable chaser.' Can't remember.

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thank for your answer, now I know why there are only few airports have with cat 3c rwy. (in fact, i only know PANC has one)ben

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