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Approach CAT I, II, III

Fri Dec 22, 2000 4:01 pm

Can anyone explain the definition of the Cat I, II and III approach and which airliners are equiped for the different categories?

RE: Approach CAT I, II, III

Fri Dec 22, 2000 4:17 pm

The differences are how bad this vis can be. Cat IIIc is your wheels touch as you see the runway!
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RE: Approach CAT I, II, III

Fri Dec 22, 2000 7:57 pm

CatI means:
That´s what you can fly when you have the Instrument rating: Your minimum is 550m RVR (Runway visulal range) and a descision hight of 200 feet above ground.

CATII means.
You need a special training and a special aircraft.
The aircraft has to have two different flight guidance systems, one autopilot, at least one operative radar altimeter. And some other small things. The approach has to be made with the autopilot. In our company and in many or almost all we have a procedure what is called "monitored approach" That means, the copilot is flying the airplane to the minimum Actually he only monitors the airplane, cause the autopilot is flying. In his mind the copilot is not landing, he always things on the mist approach procedure. And when reaching the minimum the pilot calls minimum and when the captain doesn´t say anything or when he say´s go around, the copilot is initiating the missed approach procedure.
The captain is looking outside all the time during the approach so that his eyes get used to the light . And the copilot looks inside to fly.
The minimum for a CATII approach is 350m RVR and 100 feet decision height.
At minimum when the captain has the approach lights in sight he calls "my controls" and lands the airplane. The copilot stays with his eyes on the Instruments and calls out any deviations.

CATIII means:
There are CATIII a, b and c approaches! CATIIIa means that the airplane has to have the equipment wich I have described for CATII plus a autothrottle system and an auto landing system.
The minimum is 200m RVR and 50 feet dh.
CATIIIb is the same as CATII and CATIIIa plus automatic stopping system, that means that the airplane controlles itself down to taxi speed. The minimum is 100m RVR and 0 feet dh. Thats the lowest minimum wich is allowed. CATIIIc would be possible, but it´s not allowed. The requirement for CATIIIc is the same as for the others plus automatic taxiing and automatic dogging on the gate. The minimum for this would be 0 m RVR and 0 feet dh. This category of approach is not allowed because with 0 meter RVR you the rescue troup couldn´t see anything in case something would happen.
I could give your more details about anything for example: The 777 is certiefied for CATIIIb approaches in single engine operation. I could give you a lot of detailes about certiefication requierments and other thing but that´s to much work because my AWO manual (All Weather Operation manual) has a few hundret pages.

But if you are interrested in somethin just let me know!

yes i can handle that alone. - - -famous last words
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RE: Approach CAT I, II, III

Sat Dec 23, 2000 7:57 am

Thank you very much for that detailed explanation. What kind of airplane do you fly, Benjamin?
Hope you can help me with many other questions I have.
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RE: Approach CAT I, II, III

Sun Dec 24, 2000 8:35 pm

>>CATIIIc is the same as for the others plus automatic taxiing and automatic dogging on the gate. <<

I've never heard of "automatic" taxiing. How is this function performed? Also the term "dogging" (although I've called penty of A/C dogs) is unfamiliar to me. explain, please. (I'm just a dumb Yank)
"Eagles soar. But weasels never get sucked into jet intakes.."
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RE: Approach CAT I, II, III

Wed Dec 27, 2000 3:48 am


The function automatic taxiing is not availlable, since there are no CATIIIc approaches allowed. Just imagine could you taxi an aircraft where the cockpit is 9 meters above the ground in 0 meters visibility. In that case you would need an aircraft wich can taxi automatically.

Dogging doesn´t exists it´s called docking. Sorry my fault. I think you know what is meant by it.

If you have any questions, just ask me!

yes i can handle that alone. - - -famous last words
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RE: Approach CAT I, II, III

Sat Dec 30, 2000 10:55 pm

Speaking of CAT IIIb landings, I've heard that NASA recently modified one of their planes with special differential GPS receivers and found out they could literally land a plane with GPS guidance with an amazing accuracy of within 3 meters of centerline! And that is without ILS/MLS glide-slope transponders, too.

3 meters (around 10 feet) accuracy means you can land a plane anywhere in the world even in the worst low visibility conditions. No wonder even the US Navy is sponsoring research into using GPS for more accurate carrier landings.

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