In Southern California

Guardsmen stand outside an LAX terminal. The landmark Theme Building rises in the background.  (Luis Sinco / LAT)

Captain Rojas from the 160th battalion of the California National Guard patrols LAX.  (Javier Manzano / LAT)

The California National Guard is part of the increased security presence following the U.S. Department of Homeland Security’s elevation of the national threat level for commercial flights.  (Javier Manzano / LAT)

Rojas patrols LAX from behind the wheel of a Guard vehicle.  (Javier Manzano / LAT)

Kevin Nadeau, left, and David Ray patrol John Wayne Airport with their dogs Rex and Ali who are sniffing for explosives. The four are members of the Orange County Sheriff Explosive Detection Team.  (Mark Boster / LAT)

Crowds wait to pass through the TSA inspection point at John Wayne Airport in Orange County. Long lines were the norm and all passengers were prohibited from carrying any fluids onboard aircraft.  (Mark Boster / LAT)

A Los Angeles Airport policeman stands with a machine gun as security was heightened at Los Angeles International Airport after a terrorist plot to blow up planes using liquid bombs was thwarted in England.  (Genaro Molina / LAT)

A TSA screener questions an international traveler in the Tom Bradley International Terminal at LAX.  (Don Kelsen / LAT)

A line extends outside the Southwest terminal at LAX.  (Don Kelsen / LAT)

Airport police officer H. McLeod and his dog Rex stand watch inside the Tom Bradley terminal.  (Don Kelsen / LAT)

Los Angeles Mayor Antonio Villaraigosa, surrounded by L.A. City and LAX officials, listens to Larry Fetters, Federal Security Director of TSA at LAX before a press conference at LAX.  (Don Kelsen / LAT)

An electric sign announces the security alert at Ontario airpoort.  (Irfan Khan / LAT)

TSA official Richard Lee warns Ontario airport passengers that they canÂ’t take liquids or pastes on board the plane.  (Irfan Khan / LAT)

A new security alert is posted at Ontario airport.  (Irfan Khan / LAT)

Passengers wait in lines made slow by an extra security checkpoint at Ontario airport.  (Irfan Khan / LAT)

Ontario airport police officer Adonis Cutchlow and bomb-sniffing dog Juul go through the passenger luggage Thursday morning.  (Irfan Khan / LAT)

Orange County Sheriff Explosive Detection Team member Kevin Nadeau with his dog Rex patrol John Wayne Airport.  (Mark Boster / LAT)

Crowds wait to pass through a TSA inspection point at John Wayne Airport after a heightened security alert was triggered after British offiicals announced they had foiled a plot to blow up commercial airliners with liquid explosives.  (Mark Boster / LAT)

Louise Sobieski lets her frustration show as she waits for a friend to arrive at John Wayne Airport. A heightened security alert was triggered after British offiicals announced they had foiled a plot to blow up commercial airliners with liquid explosives.  (Mark Boster / LAT)