I just came back last night from a weekend in Ireland. When we took off from Shannon Airport I noticed a sign saying "(runway number) CAT I / II" next to the runway we where about to take off from. I know this is the type of approach system for the runway, but what exactly do CAT I, II and III, stand for and mean. What is the difference between them and what are the different ways that these approaches are carried out in the PMDG 737.Luke

It's a little long to explain, and although I'm a private pilot I have no instrument rating so I could say something worng... but basically these are CATegories of instrument approaches that mainly differ regarding the minimuns (metorological minimums that is)So CAT I instument approach procedures are ILS approaches which generally can be practiced with a ceiling of 200' AFE and also a certain value of RVR (for example SBGL ILS RWY10 the RVR for the CAT I approach is 800m). However, I'm not sure if the RVR is the same for all CAT I approaches in the world. Probably not. Furthermore you'll always use MDA and not DH (minimum descent altitude vs. decision height), where one uses the aircraft's altimeter and the latter uses the Radio altimeter. Whenever you see an IAP that says only ILS RWY XX that means automatically that it is a CAT I approach.CAT II approaches are ILS approaches where the minimums get cut by half. You can thus go as low as 100'AFE (minimum celing is 100'AFE) without haing a visual of the rwy. The RVR is also half of the CAT I RVR (at least in the airports I fly to). But there's a catch. This approach can only be flown in autoland and the aircraft will now use its radio altimeter to acquire the DH.CAT III approaches are flown full autoland. The pilot is not allowed to interfere with the landing process because well - he never gets to see the RWY. RVR 0/ celing 0. All you do is hope there's nothing interferring with the ILS antennae!I probably got a couple of details wrong, so if any of our Real world tutors care to correct me thank you!Regards,Victorhttp://www.precisionmanuals.com/images/forum/800driver.jpg

>CAT III approaches are flown full autoland. CAT 3 splits further into a,b,c and CAT 3a can be hand-flown with the right equipment (for example you can do that in Gulfstream G450/550).But to make it simple to Luke - all this 'CAT' stuff is the same ILS approach and the only difference is in the 'precision' and weather minimums. Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2

The pilot is supposed to see at least some runway approach lights/runway centerline lights or runway markings in order to complete the landing in CATIIIA (Min RVR is 200 m or 700 ft; normally a DH of 50 ft is set on the radio altimeter, even technically this is an "alert height": descent down to this minimum, check autopilot is performing OK and you're in the correct position to do a safe landing and continue or go-around). CATIIIA is also referred to as "see to land", because a minimum of outside reference is still required.CATIIIB (down to minimum 75 m RVR), no visual reference is required for this approach (only full autoland) and the landing is OK if the RVR doesn't go below minimums, is also referred to as "see to taxi", because the visibility is low that only taxiing at low speeds is possible (but the majority of CATIIIB airports have a ground radar to check movements).