RobOnLI

I'm curious how this is even possible. DEN currently has a Ground Delay Program posted (I'm scheduled to fly through it today) for "UA CATI and CATII SUBS ONLY / LOW RVR". That says United Cat 1 and Cat 2 subsidiaries only due to low runway visual range.

If there are low RVR's in DEN, wouldn't that affect ALL airlines?

PS - this has already screwed my flights for the day as the inbound to my origination is delayed 2+ hours since the plane hasn't even left it's departure point this morning getting to DEN. It's an ERJ175.

-RM

seenitall

CAT1 and CAT2 refer to the landing ability of the plane and crew. CAT1 is the least restrictive (best visibility), CAT2 less so, and CAT3 means you are in real pea soup. Whether a plane can land will depend on the avionics the plane is equipped with and the training level of the crew. What this message is saying is that if the plane and crew don't have CAT3 capability and certification, conditions are too bad for them to land.

RobOnLI

Thanks. But, again, my question is why this only applies to UA. All airlines would face the same issues, no?

Or maybe I am misinterpreting what "UA" means in the GDP headline?

-RM

mduell

UA is the only big express operator at DEN. This is UA's request for the FAA to manage their express delays due to the low RVR. The other handful of express operations have few enough operations, or better equipage, that they can easily manage it themselves. As you can see in advisory 37, the conditions were below most operator's mins so the weather was impacting more than just UA Express.

Also this was a ground stop, not a GDP. I was having a hard time wrapping my head around how a GDP would be relevant here, so I looked up the actual advisories.

ATCSCC 032 DEN/ZDV 03/07/2019 DEN GROUND STOP
MESSAGE:
EVENT TIME: 07/1145 - 11/1300
FACILITIES INCLUDED: DEN
REASON: LOW RVR
REMARKS: UAL CAT1 SUBS ONLY. ZDV 2ND TIER
EFFECTIVE TIME: 071153 - 071330
SIGNATURE: 19/03/07 11:53

ATCSCC 036 DEN/ZDV 03/07/2019 DEN GROUND STOP
MESSAGE:
EVENT TIME: 11/1200 - 11/1300
FACILITIES INCLUDED: DEN
REASON: LOW RVR'S
REMARKS: CATI AND CATII UAL SUBS ONLY
EFFECTIVE TIME: 071203 - 071330
SIGNATURE: 19/03/07 12:03

ATCSCC 037 DEN/ZDV 03/07/2019 DEN AIRPORT CONDITIONS
MESSAGE:
EVENT TIME: 07/1230 - 7/1400
DEN IS BELOW MOST USER MINIMUMS. CONDITIONS ARE NOT EXPECTED TO
IMPROVE UNTIL 1400Z. USERS CAN ANTICIPATE ARRIVAL HOLDING AND
PERIODIC GROUND STOPS THAT CAPTURE APPROPRIATE CATEGORY
AIRCRAFT FOR THE CONDITONS. EXPECT UPDATES AS CONDITIONS WARRANT.
EFFECTIVE TIME: 071227 - 071430
SIGNATURE: 19/03/07 12:27

ATCSCC 043 DEN/ZDV 03/07/2019 DEN GROUND STOP UPDATE
MESSAGE:
FACILITIES INCLUDED: DEN
REASON: LOW RVR'S
REMARKS: CATI AND CATII UAL SUBS ONLY. UPDATE AT 1400Z
EFFECTIVE TIME: 071303 - 071430
SIGNATURE: 19/03/07 13:03

ATCSCC 045 DEN/ZDV 03/07/2019 DEN GROUND STOP UPDATE
MESSAGE:
EVENT TIME: 07/1200 -
FACILITIES INCLUDED: DEN
REASON: LOW RVR'S
REMARKS: CATI AND CATII UAL SUBS ONLY. UPDATE 1500Z
EFFECTIVE TIME: 071402 - 071530
SIGNATURE: 19/03/07 14:02

ATCSCC 050 DEN/ZDV 03/07/2019 UAL GROUND STOP CANX
MESSAGE:
EVENT TIME: 07/1440 - 07/1510
DESTINATION AIRPORT: DEN
RELEASED FACILITIES: 2ND TIER
REMARKS: UAL CAT 1 AND 2 SUBS GS CANX
EFFECTIVE TIME: 071443 - 071510
SIGNATURE: 19/03/07 14:43

seenitall

CAT3 avionics are expensive. It is likely far less cost-effective to equip RJs with them than mainline planes.

EWR764

Historically, of the US regionals, only Horizon was certified for CAT III operations because the PNW is always soup. For most of the other regionals, it's not worth the expense of equipping airplanes or training crews because CAT III conditions are sufficiently rare that if it's happening at a hub, the entire operation including mainline is FUBAR anyway and the regional flights are probably getting disrupted/canceled.

IIRC SkyWest/XJT are CAT II, so if DEN is at or below CAT III minima, en route flights are diverting and departures are ground stopped.

At mainline United, the fleet is equipped for autoland in CAT III conditions, but airspace capacity is generally reduced as well, with increased spacing and limited/no parallel ops, so Express is always the first on the chopping block.

RobOnLI

I took the info from fly.faa.gov. Possibly I misread it too quickly but I'm pretty sure it says GDP.

Thanks for the info.

findark

I was going to ask this -- are the majority of major airports and mainline narrowbody carriers/equipment really CAT III ready? I hadn't realized that.

mduell

Major airports and mainline operators yes, at least for CAT III A and often B. Nobody has really worked out the CAT III C taxi problem.

The following US airports have one or more CAT III approaches published: KADW KAFW KATL KAUS KBDL KBGR KBNA KBOI KBOS KBWI KCAE KCLE KCLT KCVG KDAY KDEN KDFW KDSM KDTW KEUG KEWR KFAT KGEG KGSO KGSP KGTF KHOU KIAD KIAH KILN KIND KJAN KJAX KJFK KLAX KLIT KMCI KMCO KMDT KMEM KMHT KMKE KMSN KMSP KMSY KOAK KOMA KONT KORD KORH KPDX KPHL KPIT KPVD KPWM KRDU KRFD KRIC KSDF KSEA KSFO KSLC KSMF KSTL KSWF KTPA PAFA PANC

findark

A somewhat related question - at foreign airports (like FRA), I often see hold short signs on the taxiways that say "CAT II/III". Is this the equivalent of "ILS" in the USA (and no additional holding is needed for CAT I) or is there more nuance there?

seenitall

Think of CAT I/II/III as versions of ILS. For the CAT III version to work, it needs its radio signals to get to and from the arriving aircraft without impairments due to things like multipath reflections, attenuation, etc. Big metal objects (i.e., aircraft) that are close to the guided runway tend to create such impairments. Therefore, they need to stay further back from runway thresholds when CAT III operations are in progress -- hence the separate CAT II/III stop lines.

mduell

ILS Critical Areas, as well as larger operations boundaries for CAT II and CAT III operations are pretty standardized worldwide (thanks, ICAO).

Advisory Circular 150/5340-18E Figure 3 has good examples examples of the markings and nominal locations; they've changed the figures in the latest -1L revision.

LarryJ

That type of ground delay is at the request of the mainline carrier.

In any case, if the weather is forecast to be below landing minimums at the time of arrival then a flight can not depart. That is true for all airlines and even non-airline commercial operators. It doesn't produce a ground stop, though, as each airline evaluates the weather against the capabilities of each flight individually.

At a hub airport, an airline may prefer to use a ground stop to better control the flow of traffic and manage the delays. It may be easier to skip the waiting game and go straight to rerouting affected passengers to avoid the rolling delay, inflight holding, and diversions that would otherwise occur and the chaos that this would produce. This would be especially true if the weather is marginal, fluctuating back and forth between CAT I, CAT II, and CAT III weather.

In short, you're moving the decision making up the chain to a bigger-picture view of the overall system at the hub instead of a lot of separate decisions from each flight's Captain and dispatcher.

Sykes

Here's the FAA's diagrams for localizer and glideslope critical areas. Note the different dimensions for CAT I, CAT II, and CAT III ... anything that affects all 3 would just be marked as an ILS hold, but anything that isn't inside the critical area for Cat I but interferes with the critical areas for Cat II or Cat III would be marked as such in the US as well, but at least in the US they will only define a separate Cat II/III hold if there is an operational need for planes to be in that area during normal Cat I operations.

findark

Ah, I see. I think that probably explains the general lack of the "CAT II/III" signs even at CAT III equipped airports.. if they just hold all traffic at that line even during CAT I ops then they can mark it as the ILS hold and save on signs