Fog in NYC

[mirrodie]

Our area has had some pretty dense fog lately causing many delays.

But I would think that with radar, gps and the like that fog would not prevent normal operations at a major airport.

So without going into TOO much tech, what is that whole cat 1,2,3 deal and how bad does fog have ot be before it cancels out an airports flights?

[AirtrafficController]

Fog is the most common and persistent weather hazard encountered in aviation. It is the most frequent cause for visibilities below 3 SM.
Fog can form rapidly. For example, On Tuesday, Kennedy went from VFR to LIFR in 8 minutes!
Fog obviously obstructs visibility, especially for aircraft taking off and landing. As the ceiling of the fog descends, expect ground stops. Every runway, instrument approach procedure, and pilot has minimums in terms of visibility and if he/she can conduct a procedure safely. When the visibility falls below minimums, expect go-arounds and ground delay programs.
Air Traffic Controllers in Towers rely primarily on what they see outside the window and the Air Radar, their ground radar is a secondary aid. However, as the fog rolls in and reduces visibility, air traffic operations begin to slow down or may even stop air traffic operations for safety concerns. If the air traffic control tower's visibility is obscured by fog, the local and ground controller now has to rely on only his air and ground radar (also called ASDE). The local controller may also ask pilots for help in notifying him/her if their aircraft is clear of the runway. The Category I, II, and III approaches are simply IFR ratings for pilots, aircraft and the capability of the ILS system. According to ICAO, CAT I approach has a decision height of 200 feet with a runway visual range minimum of 1,804 feet. CAT II approach has a decision height below 200 feet with a RVR minimum 1,148 feet. CAT III has sub categories but it ranges from a decision height lower then 100 feet to none, and RVR minimums from 656 feet to none.
In summary, if hazardous weather such a fog greatly reduces visibility, expect delays since air traffic operations are slowed down for the well being of aviation safety.

[steve1840]

How bad does the fog uauslly have to be to see planes get diverted away from JFK? Just curious as one of my home airports is a diversion point for JFK.

[hiss srq]

There are alot of limiters but Luke touched pretty much on everything there. It is not always an aircraft capibility that will create the limits, holds and diversions... The usual suspect is actually the available infastruture in terms of where you can hold stuff in the air or enroute as well as the actual airport itself....At JFK a company called PASSUR operates an ETT program daily and the purpose of that is two fold. One is to prevent overinnudating the ground controller with movements and the other is to maintain a steady tangible flow over the fixes one the aircraft departs. The trick is to balance the inbound and outbound flow. Arrivals enroute will usually get the priority over departures as they are already airborne but on occasion for example when thunderstorms are in the terminal area you will see N90 cut arrivals off and than holds come into play. The problem isnt soo much airplane capacity as much as controller capacity. Usually, if JFK is in a GDP or a GS it is because the demand for arrival flows is soo great that given the conditions present (Read, runway availibility) there wouldnt be enough room to squeeze departures. So, what happens is N90 will request a ground stop at that point and start punching departures out of JFK for a given duration. Once they have met their target number they will release departures to JFK and again start limiting the departures. At that point is when you will see ETT's start to grow. It's a cycle.... I could ramble on about details for a while here but I'm off from work so I dont feel like thinking about it today.

[gonzalu]

Today it was very odd... at LGA it was sunny and clear, by the time you got to GCP/Van Wyck exchange, it was completely fogged in!! Weather is awesome!

[Gerard]

Today it was very odd... at LGA it was sunny and clear, by the time you got to GCP/Van Wyck exchange, it was completely fogged in!! Weather is awesome!

Yes it is. But typical Long Island weather. The fog could roll in at any time especially with the high humidity and go miles inland or just stay at the beach. Remember two years ago during the air show that Sunday when FRG was sunny and hot but Jones was fogged in. ALMOST ruined the day but lifted enough for the demo team to go in.