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What Is CAT III/IIIa, Min Visibility For Landing?  
User currently offlineMozart From Luxembourg, joined Aug 2003, 2190 posts, RR: 13
Posted (10 years 11 months 2 weeks 4 days 20 hours ago) and read 22598 times:

Two questions here, sorry they may sound very stupid to some of you.

What exactly are the definitions of CAT I, CAT II and CAT III? WHat is CAT IIIa?

Also, what is the min. visibility in which a commercial jetliner would be able to land?

Thanks

10 replies: All unread, jump to last
 
User currently offlineB747Skipper From , joined Dec 1969, posts, RR:
Reply 1, posted (10 years 11 months 2 weeks 4 days 19 hours ago) and read 22568 times:

Salut Wolfgang Amadeus...
xxx
ILS Categories -
xxx
Cat.I - 200 feet DH - 2,400 feet (or 1,800 feet) RVR
Metric: 800 metres of 550 meters RVR...
xxx
Cat II Restricted - 150 feet DH - 1,600 feet RVR
metric: 500 metres RVR
xxx
Cat II - 100 feet DH - 1,200 feet RVR
Metric: 350 metres RVR
xxx
Cat.IIIa - 700 feet RVR - no DH (alert height generally 50 feet)
Metric: 250 meters RVR
xxx
Cat.IIIb - 600 feet RVR - no DH (alert height generally 35 feet)
Metric: 175 metres RVR
xxx
Cat.IIIc - zero ceiling, zero visibility - "blind" landing...
I believe that "la Postale de Nuit" have Cat.IIIc capability in France...
xxx
Happy contrails  Smile
(s) Skipper


User currently offlineMozart From Luxembourg, joined Aug 2003, 2190 posts, RR: 13
Reply 2, posted (10 years 11 months 2 weeks 4 days 13 hours ago) and read 22521 times:

Skipper, that was a great prelude and sinfonettia, can i just ask two more questions for the finale:

- what is "RVR"?
- when you say that there is a capability of, say, IIIc somewhere, it means the airport must be certified for that CAT, but what else? Is it a certain aircraft type, or a crew, or an airline? All of them?

Cheers

Mozart


User currently offlineJBirdAV8r From United States of America, joined Jun 2001, 4491 posts, RR: 21
Reply 3, posted (10 years 11 months 2 weeks 4 days 13 hours ago) and read 22516 times:

RVR is Runway Visual Range, basically a distance in feet that the pilot can expect to see forward in his airplane.

- when you say that there is a capability of, say, IIIc somewhere, it means the airport must be certified for that CAT, but what else? Is it a certain aircraft type, or a crew, or an airline? All of them?

The ILS equipment at the airport must be certified for it, as well as aircraft type (actually individual aircraft) and crew have to be certified.

I think there are something like only 100 or so CAT III runways in the world.



I got my head checked--by a jumbo jet
User currently offlineGE From Singapore, joined Mar 2000, 320 posts, RR: 6
Reply 4, posted (10 years 11 months 2 weeks 4 days 5 hours ago) and read 22450 times:

Hi Skipper,
Can you please explain what you mean by Alert Height?
Also, when conducting a normal ILS approach into a CAT III runway in good visibility, what would you set your DH as?
Thanks a lot!

Regards,
Russell


User currently offlineB747Skipper From , joined Dec 1969, posts, RR:
Reply 5, posted (10 years 11 months 2 weeks 4 days 4 hours ago) and read 22448 times:

Dear GE -
xxx
Alert Height (AH) is not like a Decision Height (DH) -
At "DH" (obtained from radio altimeter for Cat.II) you have to make a DECISION to land or go-around...
xxx
In Cat.III operations, there is no DH... but you have to make a decision to land based on "what you see"... pilots find the DH "decision" very convenient for Cat.II, but did not exist for Cat.III...
xxx
So in "pratical operations", the AH is used somewhat like a DH, but is not regulatory. In other terms, we expect to "see the runway" at that point... which is about 50 feet radio altimeter, just about where the runway threshold is located, in Cat.IIIa minimums. In Cat.IIIb, happens at about 35 feet...
xxx
Many 747 are equipped for Cat.IIIa operations (not Cat.IIIb), although most of the "Classic" 747s (with 3 autopilot channels) have the LRCU that is required for Cat.IIIb... LRCU = landing roll control unit... keeps the nose wheel on the center line, using the localizer...
xxx
A reminder - Cat.III is (in the 747) flown by the autopilots. Pilots simply monitor the progress of the approach, with autoflare, autoland, autothrottle and autobrakes... I only did one real Cat.IIIa ILS down to minimums in my life...
xxx
Hope this answers your questions  Smile
Happy contrails -
(s) Skipper


User currently offlineGoingboeing From United States of America, joined Dec 1999, 4875 posts, RR: 16
Reply 6, posted (10 years 11 months 2 weeks 4 days 4 hours ago) and read 22430 times:

I only did one real Cat.IIIa ILS down to minimums in my life...

So...I gotta know...how was the landing?


User currently offlineB747Skipper From , joined Dec 1969, posts, RR:
Reply 7, posted (10 years 11 months 2 weeks 4 days ago) and read 22405 times:

Nothing sensational, not even worthy of describing here...
xxx
"George" did the landing... Visibility was bad, we got a "follow me" car to show us the way for taxi...
With such automatic landings, the pilots are just "passengers"...
You just watch the annumciator lights (progress lights going amber, then green) - then check the speed and altitudes. Was like a simulator.
xxx
One little note, you will get a smile on this one -
The aircraft had LRCU - I could not taxi off the centerline - did not realize why (I simply forgot to disconnect the autopilot, the nosewheel was "tied" to the centerline).
xxx
Happy contrails  Smile
(s) Skipper


User currently offlineGE From Singapore, joined Mar 2000, 320 posts, RR: 6
Reply 8, posted (10 years 11 months 2 weeks 3 days 15 hours ago) and read 22357 times:

Thanks for the explanation Skipper. It's much clearer to me now.

Regards,
Russell


User currently offlinePanam From Switzerland, joined Mar 2000, 38 posts, RR: 0
Reply 9, posted (10 years 11 months 2 weeks 3 days 11 hours ago) and read 22329 times:

According to JAR OPS the minimum for CAT IIIa is an RVR not less than 200m.

regards

Simon


User currently offlineAAR90 From United States of America, joined Jan 2000, 3477 posts, RR: 46
Reply 10, posted (10 years 11 months 2 weeks 14 hours ago) and read 22248 times:

In Cat.III operations, there is no DH...

Actually, there is a DH for certain aircraft and/or airline combinations. Today I flew a CAT-IIIa approach/landing into DEN with 800RVR. AA 737 OpMan has a 50 foot RA Decision Height for CAT-III approaches. I believe the MD80 and F100 also have 50' DH's.



*NO CARRIER* -- A Naval Aviator's worst nightmare!
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