FlyerTalk Forums - View Single Post - A Tale of Two Suites (SFO-HKG-PEK-NRT-SEA-SFO) (Still Very, Very Long) - Part II
Old Dec 6, 1999, 11:14 pm
  #8  
greg99
 
Join Date: Sep 1999
Location: SF Bay Area
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Pshuang -

SFO, like most other airports, has certain challenges during bad weather. SFO's just happen to be worse than any other airport in the US. Flow control is the air traffic control system's term for how this is dealt with.

SFO has two parallel runways that are primarily used for arrivals (and take-offs of large or heavily fueled aircraft - or @ discretion of pilot/tower. These runways are very close together, which is not a problem during good weather, but when the weather gets bad, 2 aircraft cannot "shoot" simultaneous approaches to land on the 2 parallel runways. The aircraft have to be staggered in in a sequence. This cuts the available number of landing slots by nearly 50%.

Airlines, however, schedule for the normal, good weather number of landing slots. So, when the slots go away, and there are too many aircraft trying to land for the available slots, arrivals either have to circle in a holding pattern somewhere over Sonoma County (north of SF) or east of SF, near Modesto or Stockton. As this wastes fuel, and has the unpleasant side effect of frequently causing diversions to Oakland or SJC, ATC implements a flow control system that allots take-off times for flights around the country to try to sequence them in to SFO with the minimum delay.

The same system goes into effect when there is bad weather elsewhere in the US, particularly at hub airports, like ORD.

Hope this helps.

Greg
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