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Cat 3 Touch Down Zone  
User currently offlineKiwi1273 From United Kingdom, joined Jul 2004, 6 posts, RR: 0
Posted (10 years 1 month 3 weeks 6 hours ago) and read 2759 times:

I was asked the other day how big the touch down box is for a Cat 3 autoland.

I have found reference to must be plus/minus 27feet lateral but can find very little on Longitudanal touch down zone. I have found numbers from 200ft to 2300ft.

Anyone have any idea what it actually is

7 replies: All unread, jump to last
 
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 1, posted (10 years 1 month 3 weeks 2 hours ago) and read 2559 times:

Generally speaking, plus or minus 300 feet.
Having said this, the first aircraft to be fully CATIII certified (the Shorts SC.3 Belfast, a Royal Air Force transport) was rather unique in one respect.
During flight trials for CATIII certification, the ILS glidepath had to be electronically altered half way thru, because the runway surface was starting to deteriorate with the aircraft landing in exactly the same spot, time after time.
This aircraft, and the Hawker Siddeley Trident (the first airliner to be CATIII certified) used the same autoflight system, the Smiths Triplex autoland system.
This same general system, with imporvements and modifications, was later used in another aircraft, the Lockheed TriStar, the first wide-body aircraft to be fully CATIIIC certified.


User currently offlineAviopic From Netherlands, joined Mar 2004, 2681 posts, RR: 42
Reply 2, posted (10 years 1 month 3 weeks 2 hours ago) and read 2513 times:

Cat IIIC ??? Don't think we had MLS in those days.
Guess you mean Cat.3B




The truth lives in one’s mind, it doesn’t really exist
User currently offlineKiwi1273 From United Kingdom, joined Jul 2004, 6 posts, RR: 0
Reply 3, posted (10 years 1 month 3 weeks 2 hours ago) and read 2496 times:

411A, I managed to find an FAA document AC-120-28D that calls out the Landing System PErformnace criteria for CAt 3.

The box is alot bigger than I thought it was:

6.3.1 Landing System Performance. All types of low visibility landings systems, including automatic flight control, guidance for manual control, and hybrid, shall be demonstrated to achieve the performance accuracy with the probabilities prescribed in this section. The performance values may vary where justified by the characteristics of the airplane.

The performance criteria and probabilities are as follows:

(a) Longitudinal touch down earlier than a point on the runway 200 ft. (60m) from the threshold to a probability of 1 x 10-6;

(b) Longitudinal touch down beyond 2700 ft.(823m) from threshold to a probability of 1 x 10-6;

(c) Lateral touch down with the outboard landing gear more than 70 ft. (21.3m) from runway centerline to a probability of 1 x 10-6.

(d) Structural limit load, to a probability of 1 x 10-6. An acceptable means of establishing that the structural limit load is not exceeded is to show separately and independently that:

(i) The limit load that results from a sink rate at touch down not greater than 10 f.p.s. or the limit rate of descent used for certification under 14 CFR part 25 subpart C (see section 25.473), whichever is the greater.

(ii) The lateral side load does not exceed the limit value determined for the lateral drift landing condition defined in part 25, section 25.479(d)(2).

(e) Bank angle resulting in hazard to the airplane to a probability of 1 x 10-7. A hazard to the airplane is interpreted to mean a bank angle resulting in any part of the wing, high lift device, or engine nacelle touching the ground.



So it looks like as long as you are down not before 200ft from the threshold and not more than 2700ft form the threshold the system meets the requirements.




User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 4, posted (10 years 1 month 2 weeks 6 days 14 hours ago) and read 2393 times:

No, Aviopic...

All three aircraft that I mentioned are (or more properly were) certified to CATIIIC, using the Instrument Landing System, not MLS.

Keep in mind that it is the respective aviation authority that determines whether airlines are allowed to use CATIII, be A, B or C, for specific aircraft.

AFAIK, the only authority/airline/airport that allowed fully CATIIIC landings were,

UK ARB (now the UK CAA), using HS.121 Trident equipment.
British European Airways (BEA), now British Airways.
London Heathrow airport.

Yes, the British were the first, no doubt about it.

In addition, the SC.3 Belfast was regularly flown to CATIIIC status, in normal Royal AirForce service.

Kiwi1273,

Yes, bigger than I would have thought also.
I have personally operated the Lockheed TriStar to CATIII, and each and every touchdown has been at about 1200 feet from the threshold, and precisely on the centerline.
Having performed at least 300 autolands in the TriStar, it does indeed perform as advertised.


User currently offlineAviopic From Netherlands, joined Mar 2004, 2681 posts, RR: 42
Reply 5, posted (10 years 1 month 2 weeks 5 days 23 hours ago) and read 2324 times:

I am very sorry 411A but to my best knowledge Cat. 3c is runway guidance up to the gate which ILS does not provide.
That's when MLS or any other guidance system comes in to play.
None of them ever became a success btw.

In the following topic i posted the differences between the various landing modes.
http://www.airliners.net/discussions/tech_ops/read.main/91532/

And in this one a detailed overview in table form.
http://www.airliners.net/discussions/tech_ops/read.main/87420/



The truth lives in one’s mind, it doesn’t really exist
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 6, posted (10 years 1 month 2 weeks 5 days 15 hours ago) and read 2290 times:

You are partially correct Aviopic.
Guideance off the runway is required, but not specifically to the parking apron.

In the case of EGLL, runway high speed turnoff centerline lights have been approved.
In addition, these lights can be used to direct the aircraft directly to the correct parking position. Also, ASDE must be available and functional.

Would suggest that you contact the UK CAA and the BAA (the operators of Heathrow airport) for the details.
There are several folks still with the CAA that had input with the HS.121 Trident program, but they are fast retiring.
By the way, CATIIIC ops for the Trident were approved in November 1975.
Towing aircraft off the runway was sometimes required.
There was a period of approximately one week in the winter of '75-76 when the only aircraft that operated into/out of Heathrow were BEA Trident equipment.


User currently offlineKiwi1273 From United Kingdom, joined Jul 2004, 6 posts, RR: 0
Reply 7, posted (10 years 1 month 2 weeks 3 days 3 hours ago) and read 2146 times:

411A, what is your email address. WOuld be very interested to talk to you about a current program I am working on with a modifictaion to the Navigation System on the Tristar.



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