Precision Approach Minimums (ILS vs PAR)

[Beans]

Wouldn't it make sense for our 737s to have the Cat II and III gear (whatever that is), since it would otherwise come "standard"?

Of course, I could see the Navy, to a nonzero expense, ripping that gear out just because it didn't know what to do with it or have the time to mess with it.

 

[HokiePilot]

Those are CAT II and III ILS. Your aircraft has to be certified for CAT II in order to use the CAT II mins, or the CAT III in 0/0 situations.


Maybe I'm not understanding your question though.
I don't think any Navy a/c are certified past CAT I.

Yes, I understand that they are the rules but I am more thinking why are they the rules. Why would we need special certification to do Go down to 100 feet on a ILS, but not a PAR.

After doing a little more research, it may have to do with the decision altitude. Cat I ILSs use the barometric altimeter. The 75 feet of altimeter error means you may only decide to execute missed at 125 feet. Cat II and III ILSs utilize a radar altimeter to establish decision height. Obviously much more accurate. The radar of a PAR would give you the same benefits.

BTW, this discussion is not completely academic at the HTs. I know someone a few weeks ago take a PAR all the way to 100 ft, didn't break out and had to go missed.

 

[e6bflyer]

^
What he said. In a PAR you have your baro altitude dialed into minimums as well as a guy monitoring your height above ground who will tell you to execute missed. I wasn't alive when that thing was certified down to 100 feet, but it is and that is how the Navy has been using it. In my community, our SOP is to not go any lower than 200AGL. In a fuel emergency, of course, all bets are off.
Cat II and III ILS approaches require extra equipment AND extra training and currency requirements. Not sure if the P-8 can auto land, but even if it can, the crew would have to go through the training and periodically perform them. Most Navy runways don't have the lighting required to do anything greater than a CAT I anyway. It is a cost issue and we have the PAR at most NASs, so why bother for the one aircraft that can do it. I know -18s can also do them at the boat, but I believe it requires PALS.

 

[xj220]

A lot of it has to do with the runway itself. At one airfield, the PAR may only get you to 200 ft at one runway, but 100 ft at the next. There are a multitude of factors that go into it.

 

[xj220]

To piggyback on e6bflyer, the equipment for autoland and CAT III approaches is installed on the P-8, but because of certification, training and need, we aren't allowed to use it.

 

[pourts]

I love how the PAR is always down if its raining too hard. That used to happen all the time in Meridian.

 

[xj220]

At least in Whidbey they have an ILS to one of the runways. I like having that back up just in case and honestly prefer it over the PAR.

 

[Kaman]

Anything beyond Cat I approach minimums requires special ground facilities aircraft equipment, aircrew training/qualifications and certification. Basically, $$$...Also helps if you are able to use RAMTAFs, but that also takes $$$...

 

[jtdees]

Not sure how much bearing it has, but could it also have to do with positioning of the antennae on the ground? I remember it being pointed out specifically in Corpus that KNGP's ILS and PAR hardware were at different positions on the runway, resulting in a noticeable disparity, especially in glideslope and especially in close. Essentially, one will get you to the end lighting, while one is aimed to a good touchdown zone. Don't know how widespread that disparity is, but I remember it being a sticking point there.

 

[wink]

The training and recurrency requirements for CAT II/III are time consuming. The technical side is very costly. I still don't understand how we justify it in typical airline operations. In over 20 years at a major airline I have made maybe 8 real CAT III approaches. Yet every time I go down to recurrent, used to be every 6 months now every 9, I have to demonstrate two CAT III approaches, one to a go around. That is a lot of expensive sim time that could be spent on other training. There is never enough sim time. On the technical side the ILS equipment is essentially the same as in any other plane, just maintained to a higher standard and that is expensive. The ILS ground equipment is the same but airport markings like hold short lines and ATC procedures are different. Interestingly, approach lights don't make a difference because if you are taking it to a 50DH or less, all the lights are already behind you as you are in the flare. The real difference is the auto pilot. Again, expensive to certify and maintain. You need two independent auto pilots. To get below a 50 DH they need to be fail active so they watch each other and if one fails the other picks up and continues. On my plane they are fail passive. One fails and it just holds what its got. That is why we have a 50 DH. Having CAT III capability is a big deal in international operations where you are talking a lot of revenue, maybe a single plane that has to get in so it can turn around and pack out a lot more revenue, and often times little gas and few options to divert in bad weather. But it is my personal experience that it is a money loser for ordinary domestic ops in the US. For the Navy, not likely worth it as well

 

[Kaman]

Ironically, Wink...I was going into Philly back in January and the RVRs were below 1800, so we held over Odessa. While holding, a UPS MD-11 did a CAT III approach and miraculously after that monster blew some of the fog away, the RVR came up! We hauled ass over to 9R and made it in albeit....barely. In fact, the RVR was below right after we landed. And, we were one of the few that made it in before the airport was pretty much closed for the night.

 

[wink]

Ironically, Wink...I was going into Philly back in January and the RVRs were below 1800, so we held over Odessa. While holding, a UPS MD-11 did a CAT III approach and miraculously after that monster blew some of the fog away, the RVR came up! We hauled ass over to 9R and made it in albeit....barely. In fact, the RVR was below right after we landed. And, we were one of the few that made it in before the airport was pretty much closed for the night.

I have heard of that happening. I have never seen it on approach, but once made a take off right after someone with lower take off mins or less concern for the regs rolled down the runway blowing fog clear of the transmissometers.

 

[SharkBait]

Here at Whidbey the ILS and PAR are both about the same more or less but you can always choose to take it to the deck. It depends on how they are flight checked out. I've heard that when some of the machines aren't working as well during the flight check they will raise the minima. At Rota they were the same also 200 3/4 . Whats your opinion on the quality of the PAR approaches here at Whidbey?