mozart
Posts: 2037
Joined: Thu Aug 14, 2003 12:21 am

What Is CAT III/IIIa, Min Visibility For Landing?

Wed Nov 19, 2003 10:06 am

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
 
Guest

RE: What Is CAT III/IIIa, Min Visibility For Landing?

Wed Nov 19, 2003 10:33 am

Salut Wolfgang Amadeus...
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ILS Categories -
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Cat.I - 200 feet DH - 2,400 feet (or 1,800 feet) RVR
Metric: 800 metres of 550 meters RVR...
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Cat II Restricted - 150 feet DH - 1,600 feet RVR
metric: 500 metres RVR
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Cat II - 100 feet DH - 1,200 feet RVR
Metric: 350 metres RVR
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Cat.IIIa - 700 feet RVR - no DH (alert height generally 50 feet)
Metric: 250 meters RVR
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Cat.IIIb - 600 feet RVR - no DH (alert height generally 35 feet)
Metric: 175 metres RVR
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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
 
mozart
Posts: 2037
Joined: Thu Aug 14, 2003 12:21 am

RE: What Is CAT III/IIIa, Min Visibility For Landing?

Wed Nov 19, 2003 4:54 pm

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
 
JBirdAV8r
Posts: 3454
Joined: Sun Jun 24, 2001 4:44 am

RE: What Is CAT III/IIIa, Min Visibility For Landing?

Wed Nov 19, 2003 5:21 pm

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
 
GE
Posts: 312
Joined: Sun Mar 26, 2000 5:01 pm

RE: What Is CAT III/IIIa, Min Visibility For Landing?

Thu Nov 20, 2003 1:18 am

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
 
Guest

RE: What Is CAT III/IIIa, Min Visibility For Landing?

Thu Nov 20, 2003 1:51 am

Dear GE -
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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...
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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...
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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...
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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...
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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...
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Hope this answers your questions  Smile
Happy contrails -
(s) Skipper
 
goingboeing
Posts: 4727
Joined: Sat Dec 04, 1999 1:58 am

RE: What Is CAT III/IIIa, Min Visibility For Landing?

Thu Nov 20, 2003 2:19 am

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

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

RE: What Is CAT III/IIIa, Min Visibility For Landing?

Thu Nov 20, 2003 6:03 am

Nothing sensational, not even worthy of describing here...
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"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.
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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
 
GE
Posts: 312
Joined: Sun Mar 26, 2000 5:01 pm

RE: What Is CAT III/IIIa, Min Visibility For Landing?

Thu Nov 20, 2003 3:05 pm

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

Regards,
Russell
 
PANAM
Posts: 36
Joined: Fri Mar 03, 2000 12:54 am

RE: What Is CAT III/IIIa, Min Visibility For Landing?

Thu Nov 20, 2003 7:04 pm

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

regards

Simon
 
AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

RE: What Is CAT III/IIIa, Min Visibility For Landing?

Sun Nov 23, 2003 3:56 pm

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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