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Category III autoland (other than to "keep your hand in") is relatively rare anyway because it solves only a specific narrow problem. Suppose there is one plan

Category III autoland (other than to "keep your hand in") is relatively rare anyway because it solves only a specific narrow problem. Suppose there is one plane and it needs to land right now, but all nearby airfields are fog bound so a human couldn't land a plane there: they'd get to minimums, still not be able to see the field and abort every time until they divert to somewhere with better weather - the Cat III autoland doesn't need to see the field, it will land anyway. You have to absolutely trust the machine, this is a rare Fail Active system - humans can't necessarily help even if things go wrong so once it reaches minimums it must land the plane even if it later ceases to have 100% confidence that it can do so correctly due to systems failure. But now we're done, the plane is on the ground, on a runway, the passengers are no longer in the sky, if the plane was about to explode or run out of fuel that's awesome, but we can't do this again, autoland doesn't taxi the plane, and it can be pea soup out there, the pilots still can't see the ground even though they know their plane is firmly landed. So if there's a stack of fifty planes for JFK and it's zero visibility this technology lands one plane per runway, maybe you can land three or four, then it's effectively closed, that's 46 planes left to divert, it's not useless, especially when visibility is marginal rather than truly zero, but it does not allow the airports to stay running normally.

raverbashing 2y ago
> the pilots still can't see the ground even though they know their plane is firmly landed. They get a "Follow me" car to help the plane taxi out Slower, but it is not like the plane will stay on the runway
- tialaramex 2y ago
  For a "Follow me" car to work, you still need good enough visibility to see the car's lights. Is that always true? I'd guess that in the worst snow storms it's already not true as far South as JFK.
  - t0mas88 2y ago
    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.
t0mas88 2y ago
Agree that autolands are rare, but they are used for low visibility procedures and it's not "1 plane per runway". Almost the opposite, typically you would only use a limited set of runways in such conditions and severely limit the complexity of ground routing. Practically real zero-visibility almost doesn't happen. There will be some visibility just very very little. You can taxi slowly (think 10 miles per hour) following bright centerline lights in quite low visibility. But it would be very dangerous to manually control a landing rollout at 150+ miles per hour in that visibility.
CPLX 2y ago
This is not at all an accurate description of the typical applications of the CATIII landing procedure in practice.
ExoticPearTree 2y ago
I think you got the last part wrong. Airplanes have GPS and they know where they are on the runway, where the taxiways are and so on for all the airports they operate in. Just as they can take off in low visibility, they can also maneuver. And airports have ground radars that know where every plane on the ground is, even if the ground controllers are able to see the planes with their own eyes. Otherwise, in a lot of places airplanes wouldn't land pretty often :)

raverbashing 2y ago

> the pilots still can't see the ground even though they know their plane is firmly landed. They get a "Follow me" car to help the plane taxi out Slower, but it is not like the plane will stay on the runway

tialaramex 2y ago
For a "Follow me" car to work, you still need good enough visibility to see the car's lights. Is that always true? I'd guess that in the worst snow storms it's already not true as far South as JFK.
- t0mas88 2y ago
  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.

t0mas88 2y ago

Agree that autolands are rare, but they are used for low visibility procedures and it's not "1 plane per runway". Almost the opposite, typically you would only use a limited set of runways in such conditions and severely limit the complexity of ground routing. Practically real zero-visibility almost doesn't happen. There will be some visibility just very very little. You can taxi slowly (think 10 miles per hour) following bright centerline lights in quite low visibility. But it would be very dangerous to manually control a landing rollout at 150+ miles per hour in that visibility.

CPLX 2y ago

This is not at all an accurate description of the typical applications of the CATIII landing procedure in practice.

ExoticPearTree 2y ago

I think you got the last part wrong. Airplanes have GPS and they know where they are on the runway, where the taxiways are and so on for all the airports they operate in. Just as they can take off in low visibility, they can also maneuver. And airports have ground radars that know where every plane on the ground is, even if the ground controllers are able to see the planes with their own eyes. Otherwise, in a lot of places airplanes wouldn't land pretty often :)