SAN FRANCISCO (KGO) -- Smoke from the North Bay fires continues to spread south, causing all sorts of problems, including delays from San Francisco International Airport.
The smoke is causing delays for about one in every four flights operating at SFO. Those delays are averaging about 75 to 90 minutes, which is tolerable for most passengers.
But if you look at the arrivals and departures board, there's lots of canceled flights -- 103 so far on Thursday. That could match the 115 flights canceled on Wednesday due to the smoke and reduced visibility.
The visibility has been about 7 miles all day long. That sets into motion a kind of metering system, similar to freeway on-ramps, to control how many flights can take off or land at a time.
Normally, SFO can handle 60 flights per hour, but that number was cut in half on Thursday.
A few flights were delayed as much as 2.5 to 5 hours, but that was rare. Still, passengers took it in stride -- safety comes first.
"When they come in for landing, that's really the time when they need to be able to visually sight each other, so for safety purposes during reduced visibility, those aircraft will be separated by a greater distance from one another, similar kind of condition we would see during a foggy morning or during periods of low clouds and rain," said SFO spokesperson Doug Yakel.
"There's always delays at this airport. It's the principal problem with San Francisco, but it's a great city nonetheless," said one passenger, who declined to share his name. He did say he was headed to Denver.
The flights most frequently canceled are short hops to cities such as LA and San Diego. That's because of frequent flights where passengers on a canceled flight can be re-booked onto the next flight out.
The airport has an interesting way of gauging whether there will be smoke or fog delays. If you can't see the San Mateo Bridge from here, plan on delays.
LIST: Evacuations ordered, shelters open for North Bay fires
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North Bay fire smoke continues to impact SFO flights
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