Any examples of CAT IIIC approaches?

[Check Airman]

Hey all,

I'm wondering if anybody has any examples of airports that have CAT 3C approaches. I'm trying to settle a debate with a friend of mine.

Thanks

[eckhard]

As far as I'm aware, once the airport has installed and certified a Cat III ILS system, (which would include all the standby power and runway lighting requirements), the actual minima to be applied depend on the aircraft and operator equipment, training and certification.

The certification will be issued both by the national aviation authority of the operator and also that of the state in which the airport is situated.

So, with a Cat III approach available, the typical options may be:

Cat IIIA - DH 50' and RVR of 250m
Cat IIIB - DH 12' and RVR of 100m
Cat IIIB (no DH) with RVR of 100m
Cat IIIC (no DH or RVR)

The above are generic examples. The actual figures will depend on aircraft type and certification by the one or two states as mentioned above.

The only time I have heard of Cat IIIC being used was with the BA TriStars, but even then I think it was a theoretical capability rather than an actual operational one. I believe that they were still required to have an RVR of 50m to facilitate taxiing after landing and also to enable emergency vehicles to find them in case of a problem.

So to answer the question, you may not find any airports with Cat IIIC approaches, but there may be operators who are able to use Cat IIIC minima at certain airports.

[cortilla]

Only having done catIIIA approaches myself and no training in lower rvr's and dh's i may be wrong. However I believe the problem with catIIIC approaches and landings is the post landing phase. with no visibility you need guidance off the runway and guidance all the way to stand without the aid of being able to see where you're going.

So until airframers and airports spend the money you'll never see it happen for real.

[eckhard]

I think the BA TriStars had something called a Ground Roll Monitor (GRM) which could be set to zero and would then indicate the number of metres the aircraft had rolled. The Aerad taxi charts had headings and distances in metres for various taxiways which would have enabled the intrepid crew to find their way from the runway to the stand.

Maybe now with geo-referenced chart displays in the cockpit we could do even better?

[BN2A]

Think the Trident could do Cat IIIC approaches in the 60's/70's, but as mentioned earlier, you wouldn't be able to see to taxi off the runway and find the terminal!!

:8

[BelArgUSA]

There are no Cat.IIIC operations anywhere in the world -

In the 1970s, there were some attempts to have them in UK and France - I think with Tridents and Caravelles - also in France for the "Postale de nuit" (night air mail flights) -

Some 747-200/300 I used to fly were certificated for Cat.IIIA but were fully capable of Cat.IIIB operations - yet most airlines operating them downgraded the Cat.IIIA capability, to Cat.II in view of maintenance and training costs -

In 20 years of operations with 747, I had only 1 (I say again, one) Cat.IIIA ILS approach - all other instances, Cat.II was sufficient -

[gonebutnotforgotten]

For what it is worth from the viewpoint of someone who was involved at the time and since in setting operating minima, the BA Tristars (and all the fail operational Cat III types that followed) were never formally operated to IIIC limits as we always imposed a minimum RVR of 75m (100m in the case of the 747-400) which is in the IIIB range in the ICAO definition. This minimum was set after a bruising negotiation with the UK Pilots' union, BALPA, who were worried about the prospects of the Fire Service ever finding an aircraft in trouble in true zero visibility. One could argue at length (and we did) about whether the scenario is particularly realistic (if the damn thing was on fire, finding it would not be a major problem...), but in the end honour was satisfied when it was realised that BA simply didn't need clearance to operate in visibilities that were never observed; for all practical purposes an RVR of 75m is as close to zero as you are going to get and in the 30 odd years since the number of Cat III flights that have been affected by an RVR below limits in BA is very close to zero.

Where I believe the Tristar does deserve a place in history is that it was probably the first to be operated to a genuinely zero DH. Under FAA rules the minima may be described as 'No DH', but I believe this is a legalisitic way of saying that no DH has been specified - a sight of the ground is still needed before touchdown. The UK rules, however, do permit what it says on the tin, no view of the TDZ is needed. On the Tristar insisting on some forward view of the TDZ would have limited the aircraft to about 125m RVR, so high was the pitch attitude on touchdown. The UK CAA agreed to this interpretation after long discussion during which it became clear that no one could really say what the 'decision' on a fail operational Cat III system was for!

The BA Tristars were indeed equipped with Ground Roll Monitors, intended to help both taxi out and identification of runway exits on landing, but the minima did not depend on the GRM being servicable, which was just as well as they weren't terribly reliable. The Trident 3s were also fitted with them, but were always operated to a Cat III DH of 12 ft; the Trident Autoland system, advanced as it was for the time, never inspired quite the same degree of confidence as the Tristar's, usually described as 'PFM'. The RVR limit for the Tridents came down in stages to 75m too, so was also not IIIC.

[eckhard]

Thanks gbnf, a very interesting exposition of a pivotal time in all-weather ops!

BelArgUsa, in Air Europe we used to do 4 autolands a day if we were on a 'double Paris' or similar. Can't remember the actual wx of course, but we had Cat IIIA (50/250) on our 737-300 and -400 and I seem to recall needing it several times during the foggy season.

Now after 13 years on the B744, like you I have done but a few autolands for real. I agree that Cat II was probably enough on most of those occasions.

[aterpster]

gonebutnotforgotten:

Where I believe the Tristar does deserve a place in history is that it was probably the first to be operated to a genuinely zero DH. Under FAA rules the minima may be described as 'No DH', but I believe this is a legalisitic way of saying that no DH has been specified - a sight of the ground is still needed before touchdown.

My last airplane at TWA was the L1011, circa 1986-90. I flew a pairing quite often from PHNL to KLAX, which arrived at around 6:00 AM, LA time. During the "fog months" this was the worst hour. I made several CAT III approaches to Runway 24R where we saw nothing until the nose gear settled onto the runway. We were qualified for an AH of 100, and RVR 300, but limited at the time to RVR 600 because of the then-installed transmissometers at the airport.

We never were required to see anything prior to touchdown on the 1011. I flew the 767 for a couple of years before the 1011, with the same authorization, although I never did an actual CAT III in the 767.

[gonebutnotforgotten]

Aterpster - As I implied it was never easy for us foreigners to understand fully the FAA's position on some of these points , and I understand that individual operators can negotiate variations with their principal inspector, but some of the arguments I recall with the FAA didn't make much sense unless you assumed that they assumed (still with me?) that the pilots would seek some reference before landing, albeit not at a predetermined height. I am happy to accept that this was another misundertanding (one of many!). I am surprised though that in RVR 600 (ft) the ground wasn't visible until after nosewheel lowering, In our simulations it was visibile in RVR > 125m, say 400 ft.

[DesiPilot]

We did a lot of CAT IIIb landings at Delhi (VIDP) airport during fog season, and many a times RVR was 75/75/75. There were occasions when an aircraft would land and was unable to find their way. Many a times they'd request follow me to come to the runway so they could vacate the runway.

In my previous two companies in India we were Cat IIIb and we required NO DH and RVR 75/75/75. Any time the rvr dropped below 75 M the airport would essentially shut down. For take off we required a minimum of 125 M.

[aterpster]

gonebutnotforgotten:

I am surprised though that in RVR 600 (ft) the ground wasn't visible until after nosewheel lowering, In our simulations it was visibile in RVR > 125m, say 400 ft.

Eye height in the 1011 is supposedly higher than a 747's at moment of touchdown. Having said that, perhaps the HIRLs and TDZ lights became visibile at some point between touchdown and the nosewheel touching on. Once we felt the mains touch on, my eyes were looking more at instrument verification of centerline tracking.

How nice a HUD would have been!

[petermcleland]

The Trident CAT IIIb limits were a Decision Height of 12 feet Radio with RVRs of 75 metres at touchdown end, 50 metres at midpoint and 50 metres at far end. The visual requirement for me to say "Land" as opposed to "Overshoot" was that I see ONE LIGHT. I did a few for real and of course hundreds in the simulator on bi-annual checks.

Heathrow had a special radar mounted on the tower in those days and they were capable of talking you to your stand...I used it a few times and it was impressive. It easily got you on to the green lights taxiway centre line and then warned of approaching turn off points. I had to use it years previously on the Vanguard when the fog clamped in suddenly. I think that radar has now gone...It was a white dome topped thing on the side of the tower at the top.

[Check Airman]

Thanks for the info. All the charts I have seen thus far have had CAT 3C NA in the minimums section. And thus 3B is the best you can do legally.

Somebody mentioned that there may be airlines certified to use 3C minima at some airports. Does anybody know of any examples?

[mustafagander]

Minima is all very well to land but you must be able to taxi off the runway. Sometimes we in my mob find this as a limit.

There's simply no point in being able to land, except in an emergency, and then being unable to taxi to the gate, is there?

[aterpster]

mustafagander:

There's simply no point in being able to land, except in an emergency, and then being unable to taxi to the gate, is there?

There have been a few tow-ins at LAX over the years. It's a long process.