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I was going to an airport with weather at minimum for CAT I approach. Not wanting to know whether or not I could make it I thought about asking ATC if I could do a CAT III approach even though the weather was still above minimum for CAT I. Eventually the weather got better but my question is: Could I have requested from ATC and be granted a clearance for a CAT III approach (abiding by the CAT III weather mins) even thought the current weather was above CAT I minimums?

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  • $\begingroup$ In order for ATC to clear you for an (operational, not practice) Cat III approach, the airfield would have to operate under Cat III Low Visibility Procedures (see skybrary.aero/index.php/Low_Visibility_Procedures_(LVP)). As these are normally very restrictive in terms of permitted movements on the airfield and especially around runway areas, I would expect airport operators to only invoke LVPs to the level that is operationally required. Therefore I would assume that the answer would probably have been “no”. $\endgroup$ – Cpt Reynolds Mar 6 '18 at 20:23
  • $\begingroup$ Possible duplicate of How do you choose CAT II vs. CATIII ILS? $\endgroup$ – fooot Mar 6 '18 at 20:24
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    $\begingroup$ Not a duplicate at all. This question is, CAN I fly the Cat III; the other question is "when might one choose to fly ..." one approach or the other. $\endgroup$ – Ralph J Mar 6 '18 at 22:40
  • $\begingroup$ My airlines is very specific about this. If the weather is below CAT I, always do CAT III (assuming all requirements are met) $\endgroup$ – Antonio Mar 12 '18 at 12:52
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Yes, you can request it. We (ATC) may or may not grant it. It can be quite complicated for us to establish CAT II/III procedures, including having to switch over to backup power, turning on stopbars and other protective measures, limiting aircraft and vehicle movements on the maneuvering area, closing certain taxiways etc.

Doing a CAT III approach is not just looking at a different chart, it can involve a lot of complicated procedures for the airport!

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  • $\begingroup$ Switch to backup power ? $\endgroup$ – cavver Mar 7 '18 at 18:46
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    $\begingroup$ If the weather is marginal like OP is describing, would ATC usually be prepared to switch to CAT II/III if requested? $\endgroup$ – TomMcW Mar 7 '18 at 20:18
  • $\begingroup$ @cavver Where I work we will switch to diesel generators during LVP because they are more reliable than external power. The system will then fall back to external power if a diesel generator fails (switch over time less that 1 second during LVP) $\endgroup$ – J. Hougaard Mar 8 '18 at 13:41
  • $\begingroup$ @TomMcW Yes, of course. $\endgroup$ – J. Hougaard Mar 8 '18 at 13:42
  • $\begingroup$ J.Hougaard .. thank you for your valuable answer. $\endgroup$ – Antonio Mar 12 '18 at 12:54
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I assume that the airport has a published CATIII approach chart , i.e. the ILS system is CATIII ready . You should request a protected ILS .approach from the ATC. See what happens when doing an autoland without requesting it to be protected

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