3 ms·

Low visibility due to fog happens regularly in places like Amsterdam and London. You can see taxiway centerline lights or a follow-me car in that, but you can't

Low visibility due to fog happens regularly in places like Amsterdam and London. You can see taxiway centerline lights or a follow-me car in that, but you can't manually land in it. Below 300m / 1000ft visibility you're down to autoland cat III while you can taxi in that with no problems.

tialaramex 2y ago
How often do you think they actually do Cat III out of necessity, at say Heathrow or Schiphol ? My guess would be that having Cat III capability makes them comfortable - because they can land planes anyway if they need to, but it isn't often (maybe 2-3 days per year) actually used "in anger" so to speak. Cat I and II autolandings are common, because they mitigate visibility problems while leaving the final decision to a human pilot, but the pilots don't like Cat III precisely because they get this job to fly and in Cat III you're not flying the plane. And yes, as I noted, when visibility is marginal you could continue normal operations with Cat III at a reduced pace and Heathrow has been known to do that, but it's extremely disruptive. The problem is that as visibility reduces our options continue to narrow further. At just Cat IIIa where as you say the pilots can just see the signs and drive down a taxiway without problems, Heathrows targets 50% capacity, and as things worsen that falls, to 10% and eventually the airport is closed to normal traffic. Why low capacity at just Cat IIIa? Because of radio protection, the aeroplane is made of metal, so you need to reduce pace so that there's no risk of interference from the plane ahead of you during your autoland approach. If you were visual, even in Cat II, you'd be fine because you can see if there's a problem and abort, but in Cat IIIa you're absolutely reliant on radio beacons so there cannot be any problems.

3 ms·

Low visibility due to fog happens regularly in places like Amsterdam and London. You can see taxiway centerline lights or a follow-me car in that, but you can't

by t0mas88 2y ago

tialaramex 2y ago
How often do you think they actually do Cat III out of necessity, at say Heathrow or Schiphol ? My guess would be that having Cat III capability makes them comfortable - because they can land planes anyway if they need to, but it isn't often (maybe 2-3 days per year) actually used "in anger" so to speak. Cat I and II autolandings are common, because they mitigate visibility problems while leaving the final decision to a human pilot, but the pilots don't like Cat III precisely because they get this job to fly and in Cat III you're not flying the plane. And yes, as I noted, when visibility is marginal you could continue normal operations with Cat III at a reduced pace and Heathrow has been known to do that, but it's extremely disruptive. The problem is that as visibility reduces our options continue to narrow further. At just Cat IIIa where as you say the pilots can just see the signs and drive down a taxiway without problems, Heathrows targets 50% capacity, and as things worsen that falls, to 10% and eventually the airport is closed to normal traffic. Why low capacity at just Cat IIIa? Because of radio protection, the aeroplane is made of metal, so you need to reduce pace so that there's no risk of interference from the plane ahead of you during your autoland approach. If you were visual, even in Cat II, you'd be fine because you can see if there's a problem and abort, but in Cat IIIa you're absolutely reliant on radio beacons so there cannot be any problems.