Basil

When I went through OATS we were taught:

CAT 3b was 75m RVR and No DH (minimums)
CAT 3c was 0 RVR and 0 DH

but would need some method of using instruments to taxi all the way to the gate as with 0 RVR you ain't seeing anything at all. Hence why it is never used in reality.


152 Captain

Now I'm in the real world, on the A319/320 the aircraft can fly to

Cat 3B WITH a DH, in our case 25ft
or
CAT 3B NO DH, ie 0ft

The Performance manual states the lowest limits that we may use for every airport we visit as some only allow Cat3B WITH DH.

The reason in our case for the 25ft limit is that if a go-around is initiated below this height the aircraft may contact the ground (think of a bounce), so it would not be sensible to have a DH below this value unless it is 0 DH (ie the main wheels would be on the ground before you saw anything).

For info, our A319's and A320 CFM's used to be 17ft DH, the 25ft limit got introduced when we added A320 IAE's which for some reason had a higher DH, and the company wished to be consistent so took the most limiting case. All the aircraft can land to 0 DH if allowed to.

Oh dear! oh dear!

Having now summoned Mrs NorthernSky to bring my cocoa and 'special pills', I shall attempt to put a few records straight:

(i) HUDs are marvellous. You can do all sort of things with them which appear impossibly dangerous until you train and try. Manual Cat3a is one of these. (Shooting people down is another!)

(ii) Some aircraft have difficulties with manual landings off Cat 2 approaches, such as B737 300-900 non-Cat3b. This is down to the autotrim, which is the system Boeing had to fit to get around their totally inadequate flight control systems when autoland came in. Future aircraft will have a reasonable system with rollout guidance etc. allowing Cat3b.

(iii) Some aircraft place different relative weightings on different inputs. For example, at Leeds (sloping ground on approach) the B737 can autoland to Cat 3a because it pays little heed to the RA and delta-RA (this is why it floats like a liferaft in the flare for an autoland), whereas the Fokker 100 can only do Cat 2 manual landings because it pays more heed to the aforementioned (which, in turn, is why it greases on most of the time if you let it do its beautiful thing). Allied to this is that many Boeing pilots muck about with the Thrust Levers in the flare when autolanding. Not necessarily a good idea...

(iv) Cat 3b only has a DH if the aircraft can't manage without it (more complex than this of course, but to state a DH for Cat3b is wrong).

(v) Even off a Cat 3a approach with DH 50ft RA you may well touch down during a go-around. That's life, and the experts tell me it won't kill me. Which worries me, because they keep telling me that I'm one if them, and I can only guess!

(vi) Cat 3c is dead and gone because taxying is so tricky.

ps All this talk of the wonderful Fokker makes me wonder whether I shall ever fly one again - anyone needing a pilot for a big and beautiful pencil-jet? That wing, those controls, the not-having-to-bother-putting-flaps-out-for-take-off...

Why have a decision height?
IMHO its a legal thing.
If the pilot does not have a decision height at which to decide to land or goaround who are you going to blame if it ever goes wrong?

Same person you blame if it goes wrong on a visual approach!

Bigjim:All airline pilots are qualified to land in fog. Its the thickness and density of the fog that governs if the pilot can land. There are lots of ifs and but though.....

As a pilot progresses as a pilot he/she can take further qualifications that allows him/her to land in thicker fog. These greater qualifications are called Cat II and Cat IIIa,b,c . Cat IIIc basically allows the pilot to let the aircraft land itself in virtually impeniterable fog.

Even if the pilot is qualified up to CatIII they can only land to the limits of the lesser rated pilot on the flight deck. ie if one pilot is Cat II and III and the other is only Cat II the flight is limited to Cat II minima.

Even if both pilots are Cat III, if the aircraft has a minor defect it can result in the aircraft not being Cat III able.

As a final point the airfield itself has to have been tested and cleared to a specific Cat level.

As a final point the Ryanair aircraft are generally cleared to Cat IIIa and the crews are mostly trained to that level, unless very new to the airline. Your diversion to Bournemouth could have been due to a multitude of reasons. I was flying that night and both myselft the captain and the aircraft were all Cat III and landed twice no problems.

So why not equip all a/c with CAT IIIc equipment? Is it bigger physically to install? And is that true that if one of the crew doen't have the required qualifications, then the aircraft diverts? Sounds well weird that! Obviously it's a rule for some reason or another though. Are full autolands a bit....well, you know.....SCARY?!:(

Lump Jockey: It would be great to equip all the aircraft with CatIIIc equipment, however different aircraft of different generations ie 737-100 and 737-800 have different though similar systems, even within the same generation depending what was specified by the original purchaser. Think of it like buying a car , you have all the options for all the toys from new, depending on you budget, but if you buy secondhand you take what you get. Its not just a matter of slapping in a 'CatIIIc box'. To make the aircraft C3c would involve changing many many components and avionics systems, and in the end would be hugely expensive for the one or two occasions in the year when it is needed.

Yes if one of the pilots isnt qualified the aircraft will divert. Flying as a whole is covered by a multitude of backup systems. What would happen if something went wrong very late and low on a C3 approach , ie the qualified pilot collapsed? Also the approach isnt just flown by one of the pilots it is flown by both, generaly the First Officer (F/O)will fly the aircraft on instruments to the decision height ie 50ft (or lower) whilst the Captain monitors the approach and looks out the window. At decision the F/O calls decide and the Captain will say land, if he can see the runway and takes control whilst the F/O remains on instruments, or he will say Go around and the F/O will fly the go around. Its not a one man band!

Hope that explains things a little better....

I fly the Jetstream 41 and we have a limit of 100ft and 300m (with no requirement for any RVR in the mid and stop end) for a Cat 2, which is always a manual landing as our autopilot cannot land the aircraft. The other night at Leeds, we did at Cat 2 with a 10 knot tailwind - we can accept that on 32 (which is the only Cat 2 runway at Leeds) as we are small and it doesn't take us ages and ages to stop. The Jets however cannot, so they all went to Manchester or Teeside! Ho ho! We were the only commercials that got in.

For our Cat 2's the Captain flies the approach in Auto and the First Officer monitors the instruments. Captain looks out from 100 above decide and First Officer keeps heads in. Auto is disengaged at 80 ft, Capt looks out and FO keeps looking in giving advice if there is any deviation. I have only flown a couple down to real minimums, but I quite enjoy it. Very surreal when a few runway lights slowly appear a few seconds before landing.

I'm not a pilot, no where near it. But I do enjoy aviation and would have loved to have been a pilot! The reply I got there from batty was awesome, and a new appreciation of your fabulous job, I now have!:) Sounds great!:D

Particularly interested in the comments of those who have clearly experienced the 'joys' of Leeds on a foggy day. The installation of CAT3 on 32 has made things better than in the past, but as J-Rider and Northern alude to, the slope & the seemingly everpresent tailwind seem to limit its usage to everything other than J41s, 146s and empty Embraers!

The question is, what can be done to improve matters. Can the CAT3 system on 32 be improved? If so, how? Is manual CAT2 possible on 14 with the 3.5 degree glide. The ability to get in with a 300m minima on 14 would elimate the majority of the current diversions.

Comments appreciated.

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