KSEA CAT III Procedures

[tman41291 4]

I tried to google this, but came up short. Might of just been typing it in wrong, but was hoping someone on here can explain the KSEA CAT III procedures a bit more to me. Ideally the chosen runway is always gonna be favored by the wind, as such if you are landing at KSEA on the rwy35's and these runways are all Cat I only approaches; what happens when you need a Cat III approach (which are only on rwy 16's) but the wind is favoring the rwy 35's? Hopefully i didnt make that too confusing sounding, just curious because if im coming into land, i dont want to land with a heavy tailwind, but i need the Cat III approach.

[cmpbellsjc 2,963]

The differences are explained here in the ILS Categories section: https://en.m.wikipedia.org/wiki/Instrument_landing_system

 

But, in the sim you can just fly the CAT I approach as you'll get the same results.

[ubersu 78]

I tried to google this, but came up short. Might of just been typing it in wrong, but was hoping someone on here can explain the KSEA CAT III procedures a bit more to me. Ideally the chosen runway is always gonna be favored by the wind, as such if you are landing at KSEA on the rwy35's and these runways are all Cat I only approaches; what happens when you need a Cat III approach (which are only on rwy 16's) but the wind is favoring the rwy 35's? Hopefully i didnt make that too confusing sounding, just curious because if im coming into land, i dont want to land with a heavy tailwind, but i need the Cat III approach.

 

Then you better consider diverting to another airport. CAT1 and CATIII are predetermined and can't be arbitrary. If a runway doesn't have a CATIII approach and you need one, you'll have to go elsewhere.

 

DJ

[BrianW 124]

At any airport regional weather patterns are always taken in consideration when spending the time and money to fund an approach.  In the Puget Sound area, low pressure/bad weather winds almost always comes from the southwest, while high pressure/good weather produces wind from the northwest. Even on the rare days this isn’t the case the 200’ minimums of a standard approach are more than adequate around here a majority of the time, and when they’re not it usually is due to fog and that means little or no wind.  

[Airline2Sim 489]

CATIII conditions (i.e. you can't see your hand in front of your face) are almost always in very still air so the wind isn't usually an issue. Most aircraft can handle a small tailwind for CATIII autolands, too.

[tman41291 4]

Just curious because Miami for example who has heavy winds AND heavy rain which can sometimes warrant CAT III approaches. KSEA may be different as far as their weather goes, but i know Miami is like that so wasnt sure as to why CATIII would only be on one side of the runway.

[DaveS 144]

If there are heavy rain and winds at the airport, you'd likely be holding or diverting anyway rather than trying to land in a full blown thunderstorm. MIA,in your example, doesn't even have CAT II or III ILS's

[Airline2Sim 489]

Just curious because Miami for example who has heavy winds AND heavy rain which can sometimes warrant CAT III approaches. KSEA may be different as far as their weather goes, but i know Miami is like that so wasnt sure as to why CATIII would only be on one side of the runway.

It's pretty expensive to maintain CATIII capability and some approaches simply can't have it because of the local terrain etc. It may be that it's not worth having it on both ends due to the prevailing winds or on cost or logistical grounds. And in heavy winds the visibility is normally pretty good. It's still air that produces low visibility.

[tman41291 4]

Ahh okay, well i appreciate the replies! all a learning experience for me

[Angelo Cosma 61]

The Runways are 16 / 34, and both ends have CATIII runways. The Flight Crew, Aircraft, and Airport have to be CATIII Certified and equipped. 

 

Those approaches are always available, what changes is where aircraft, vehicles, etc hold short of the runway. Those ILS hold short areas are respected when the weather is poor or if the Pilot advises ATC he is performing an Auto Land. 

[tman41291 4]

The Runways are 16 / 34, and both ends have CATIII runways. The Flight Crew, Aircraft, and Airport have to be CATIII Certified and equipped. 

 

Those approaches are always available, what changes is where aircraft, vehicles, etc hold short of the runway. Those ILS hold short areas are respected when the weather is poor or if the Pilot advises ATC he is performing an Auto Land. 

Oh okay, i was just going off the charts. The charts state they only have CAT1 on the 34's. The lighting on 16 is ALSF2, but the 34 is MALSR, which i was under the impression the ALSF2 are for CAT II and III approaches because they have extra lighting.

[ESzczesniak 128]

The Runways are 16 / 34, and both ends have CATIII runways. The Flight Crew, Aircraft, and Airport have to be CATIII Certified and equipped. 

 

Those approaches are always available, what changes is where aircraft, vehicles, etc hold short of the runway. Those ILS hold short areas are respected when the weather is poor or if the Pilot advises ATC he is performing an Auto Land. 

 

Are you sure?  I'm not a pilot and don't fly at SEA, so I'm not swearing I'm right.  However, looking at charts on Airnav.com, the 16's have CAT III's, while the 34's only have CAT II's.  To go from a CAT II to CAT III is not a very common weather condition in the real world, so logistically probably not a big issue.  I believe most (if not all?) aircraft can perform and autoland on CAT II or III, the difference is just DH.  Even that, if I'm recalling correct is not always dissimilar with CAT II, and CAT IIIa/b being 50', while CAT IIIc is the 0/0.  

 

And I believe a lot more than just the hold short lines change.  In particular, I believe that as CAT increases, terrain clearance requirements increase and the equipment itself has higher requirements. 

[Angelo Cosma 61]

Yes, there are a lot more factors that come into play other than protecting the ILS Critical area, but the most obvious and easiest for the OP to understand would be that. 

 

Aircraft can land CATII and yes the weather minima is not as low as CATIII. Generally with weather visibility that poor there is little to no wind, so the 16s would be in use to facilitate CATIII. 

 

Then you have RVRs (Runway Visual Range) certain airlines need a certain distance to legally takeoff or land, Vertical Visibility is another criteria set by Airlines / Flight Crew certifications, the approach lighting system, the list goes on. 

 

The OPs question about the operation and how approaches are chosen or assigned, I was giving him a brief quick overview. 

[skelsey 765]

believe most (if not all?) aircraft can perform and autoland on CAT II or III, the difference is just DH.  Even that, if I'm recalling correct is not always dissimilar with CAT II, and CAT IIIa/b being 50', while CAT IIIc is the 0/0.  

 

And I believe a lot more than just the hold short lines change.  In particular, I believe that as CAT increases, terrain clearance requirements increase and the equipment itself has higher requirements. 

 

As Angelo says, there are many requirements. For BA at least (and I presume most other operators) an autoland is SOP off both CAT II and CAT III approaches.

 

The main issue as already mentioned is that for CAT II and III operations where aircraft are autolanding it becomes essential to protect the integrity of the ILS signal. This means that unlike during normal CAT I ops where only the critical areas need be protected, for CAT II and III ops the much larger localizer/GP sensitive areas have to be protected. This is, amongst other things, what LVPs (Low Visibility Procedures) are designed for, and essentially it means that departing aircraft have to be held further away from the runway when holding short and landing aircraft need to be completely clear of the localizer sensitive area before the next aircraft can pass a particular point (usually the FAF). As you can imagine, this means big gaps between arriving aircraft, and even bigger gaps if you need to depart aircraft in between arrivals, which is why the landing rate goes down the pan when the visibility drops.

 

This also means that airports are generally reluctant to implement LVPs unless they have to (because the reduced flow rate causes chaos). If LVPs are not in force, the ILS sensitive areas will not be protected and therefore an aircraft on approach may experience undesirable signal fluctuations. This is why autolanding off a CAT I approach without LVPs in force should be done with extreme caution -- there's fairly dramatic video on Youtube of a Singapore B777 going grass-cutting at Munich as a result of a CAT I autoland -- an aircraft departing ahead overflew the localizer array and distorted the beam, resulting in the landing and rollout going very wrong.

 

In addition, (in EASA land at least) the law says that the DH must be determined by use of a radio altimeter. This means that a) you have to have a radalt fitted and operational and b ) the terrain on the approach has to be surveyed in order to determine the radio DH -- if the terrain under the final approach is particularly undulating this may preclude establishment of a CAT II or III approach (interestingly, Manchester, UK (EGCC)'s runway 05L is CAT III certified but not CAT II -- this is because of a valley that runs under the approach path at the point where the CAT II MAPt ought to be. Because this causes unacceptable inaccuracies in the radalt, CAT II is not authorised -- but there's no issue with CAT III because the much lower (or indeed zero) DHs are essentially over the threshold and the surface there is flat enough to make the radalt reliable!).

 

To maintain CAT III certification, the ILS itself has to be flight checked regularly and there has to be a redundant "no break" power supply for both the ILS and the approach lighting to ensure that there is no interruption in case of power failure at the airport (again, the backup gens may not necessarily be running if LVPs are not in force).

 

Plus of course the aircraft has to be certified (it has to log a successful autoland every now and then) and so do the crew (through initial and recurrent theoretical and sim training, and if necessary the occasional 'real' autoland for currency as well).

 

There's a lot to it!

 

As mentioned above, if the weather is below minima for the category of approach that is available and that you are flying (say the runway is only CAT II and the RVR is below the CAT II minima of 300m) in Europe at least there's an "approach ban" -- you're not even allowed to continue an approach below 1000ft AAL -- the idea being to avoid the tempation to go down and "have a look". If the RVR deteriorates after you have passed 1000ft on the approach then you can continue to DH, but in any event if you don't get the necessary visual references then a go-around is mandatory. There's no room for messing about in these sorts of conditions -- there have been far too many accidents and fatalities as a result of crews continuing below DH without the mandated visual references (the most recent well-known example being a THY A330 at Kathmandu).

 

If the wind is out of limits for the CAT III runway then obviously you used your superior piloting judgement before departure to load some extra fuel and you either wait it out to see if it improves or divert somewhere with better weather!