The numbers thrown around by the FAA and SFIA vary depending upon what they are trying to do. Since they want to build runways into the Bay, they don't want to find solutions that don't require runways. Thus, the arrival rate that SOIA would allow keeps getting lower. They started out at 45 planes/hour and have continued to reduce that number. But Williams Aviation points out that SFIA just lowers the number without justifying them. Single runways at other airports support higher rates of operations in bad weather than SFIA is claiming for SOIA at SFIA.

In the Draft Environmental Assessment for SOIA, SFIA said that SOIA would allow side-by-side arrivals as much as 18% of the time in some months. The best month for using SOIA is March and the worst is July according to the EA. The plot below shows the per cent of the time SOIA could be used in those months by time of day.

Not unexpectedly, for those who live in the Bay Area, there's a marine layer in the mornings which tends to dissipate by 11 AM or so.

Be sure to note this is only the time that SOIA could be used. If the weather is good, then SFIA can land two streams. How often does that happen, you ask? According to SFIA consultant P&D Aviation*, SFIA can land two streams 84% of the time - that's the average.

* Analysis of SFIA Runway Reconfiguration, Summary Report, Page 3-9, Jan. 22, 1999