CAT III Approaches

[airgator]

Any military guys/gals doing real world CAT III?

 

[KC-10 Driver]

Yes, but not with the military. Not the answer you're looking for, I presume.

What, specifically, are you wondering?

 

[Benhuntn]

AF 1 the B-747 and AF 2 the B-757 are Cat III capable. I am sure there are others.

 

[airgator]

Yes, but not with the military. Not the answer you're looking for, I presume.

What, specifically, are you wondering?

I am going through C-5 AMP training and was just surprised that the AMP jets are now CAT III capable. I figured the 737/747/757's and Gulfstreams were also but am curious what other airframes have the capability.

 

[Gorilla]

Doesn't the C-17 have CATIII?

My wife works for Lockheed. A few years ago, they were looking at the C-5 upgrades, and I had just transitioned to the HUD-equipped B-737-800. I wrote a proposal for my wife advocating a HUD retrofit for the new C-5 avionics, rather than make them CATIII autoland. A HUD allows hand-flown CATIII, and the gist of the proposal was that a HUD would be FAR cheaper and much more reliable than setting the C-5 up for A/P autoland; plus, the HUD could be tied into the FMC and allow the C-5 drivers to land at ANY field down to a very low vis. It would also dramatically increase the accuracy of airdrops and other cargo associated goodness. Any battle damage would be far more likely to disable a component of the A/P autoland than it would the HUD.

I thought the proposal was sound, and couldn't believe it was rejected. The Air Force wanted autoland, period.

 

[pkober]

Don't worry about Cat III in the C-5 because it will break somewhere enroute with better weather and per diem.

CLAMBAKE

 

[firstthird]

I fly the B737-700 (C-40A) for the Navy in the reserves and although the aircraft is capable of a Cat III, we do not do them. Our wing limits us (and all Navy VR assets) to a 100 foot DH. Probably a good idea in that our Cat II procedures are not quite up to 121 airline standards since we do it too infrequently and have too many guys at too many different airlines to get the same level of standardization that a 121 operation regularly attains.

We do the Cat II with either HUD or autoland. Gorilla mentioned that with a HUD then the C-5 could've done really low mins at any field. Don't think that I can agree on that one. Without an ILS, the HUD does nothing to lower landing mins here at SWA. (just reread Gorilla's post, the part about tying it to the FMC, yep guess that would work, but then you are flying approaches that aren't really there, no TERPS, etc. scary stuff, IMO. although maybe tactical platforms do that kind of stuff all the time for all I know)

SWA has a few approaches that grant us slightly lower visibility mins with the use of a HUD (regular CAT I setups) but to really get full use out of a HUD, the approach you are flying needs to be CAT II/IIIa, for all of the obious reasons.

So, short version is that since very few fields that the Navy flies to have CAT I ILS, much less CAT II or III; the ability to do a CAT III approach is more cool in the abstract than actually useful in reality. Now, any navy aircraft that has two pilots can do a PAR down to 100 & 1/4 but that is a whole different story.

 

[Gorilla]

I was referring to the technical ability to "build" an approach to pretty much any field based upon GPS data. In war, you do what needs to be done.

 

[RampFreeze]

I was referring to the technical ability to "build" an approach to pretty much any field based upon GPS data.

The HUD doesn't get you anything that an FMS approach without a HUD would. If you look at the RNAV RNP approaches ( Not RNAV(GPS) ) that are being used (i.e. KDCA, KPSP, etc.) there isn't a HUD requirement. You just follow the needles like any other approach, heads up or heads down.

A HUD can get you lower takeoff mins though, but I doubt the USAF would ever go for takeoff mins where the HUD would be effective. At many airlines a HUD allows you to drop your takeoff mins on a runway with centerline lighting, etc from 600 RVR to 300 RVR. Most USAF heavy aircraft have takeoff mins up at 1000 RVR or 1600 RVR depending upon the mission. So, the HUD wouldn’t get you anything there unless they made some drastic policy changes. A HUD could give you the ability to fly hand-flown CAT IIIA approaches though…

Back to Cat III - Cat IIIA mins (700 RVR or as published) are available to USAF VC-25, E-4, (747s) and C-40Bs.(737/BBJ) USAF C-32s (B757) are Cat IIIA and Cat IIIB capable (300 RVR or 600 RVR as published). Every other airframe is Cat II ILS or higher for mins. Haven't heard about the C-5 AMP but it is good to hear if they are joining the Cat III club.

Big difference between Cat IIIA and Cat IIIB (other than 400 RVR of vis required) is that Cat IIIB aircraft have 3 autopilots, etc that allow the system to be what is called "fail operational" where the loss of one system at the worst moment doesn't leave you hanging on one system that you "hope" is working correctly. For a Cat IIIB approach, there is no Decision Height, you don't have to see anything before the automatic landing, ATC just needs to be calling 300 or 600 RVR. Cat IIIA usually involves a 50' Decision Height where you need to see some lights.

Probably more than you ever wanted to know...

 

[Gorilla]

I'm not a CATIII genius. I fly them and I know the legalities. I do know that there is painful, ancestor-worshipping inertia associated with precision approaches, and that GPS/RNAV capabilities are NOT being used to their full extent. The HUD, equipped with its excellent and sensitive FPV and flight director, is ready for the day when the accuracy of GPS, and GPS-derived RNAV approaches, are freed from artificial constraints imposed by both the FAA and the military.

Autoland, as opposed to precision HUD approaches (and note that I am not referring to ILS), are two entirely different beasts. In some future conflict, you have two C5's, one HUD equipped, and the other multiple-autopilot autoland equipped. The aircraft must be dispatched with a critical load to a rough field, no ILS.

Lacking ILS, autoland is out. Now it's down to FMC RNAV flight director, vs the identical system but pumped through a HUD. There is no doubt that the HUD is vastly more capable than a head's-down FMC RNAV approach. The HUD not only provides all necessary cues, it also will outline the approaching runway environment in a synthetic display, and can display terrain avoidance as well.

My entire rationale was that autoland is antiquated ancestor worship; expensive, of limited application due to the need for both a calibrated and certified aircraft and a ground-based ILS at the destination, and the dispatch rate for HUD vs full autoland is superior.

Compare the list of required systems for AP autoland on a B767 vs a HUD CAT3 approach on a B737. The 737 list is about 1/2 as long as the 767. The HUD simply is a better option. It can do it all right now, and in the future, it can do more than FMC RNAV. Cheaper to boot. All we need to do is get the powers that be to unleash the full capabilities of GPS LNAV/VNAV and stop worshipping at the altar of the antique ILS system.