An American Airlines flight bound for New York City was halted just before takeoff Thursday after someone called in a threat, and two people were detained.
The two people were being held for a "separate detention" but they were being questioned about the incident, and all other passengers would be questioned as well, said Joe Schadler, a spokesman for the FBI.
"Somebody called and advised that there was a threat to this plane," Schadler said. "We have to take that seriously."
He said someone called in a terror threat against the plane but he would not disclose where it came from, other than confirming the call was not from someone aboard the plane. The threat was deemed "non-credible."
It was not clear if it was a bomb or hijacking threat, but a second federal law enforcement official who received an investigative update on the case says it was not a credible one.
The threat report originated from clerk at a business in Alameda, a city across San Francisco Bay from the airport, said Lt. Bill Scott. The clerk called dispatchers at Alameda Police Department shortly after 9 a.m. Thursday and said her business had received an anonymous phone call "making a threat specifically about Flight 24," Scott said.
Police handcuffed a man and a woman who were seated in the back row of the plane. Michael Kidd, who was on the flight said he saw a young man and a young woman sitting in the back row being taken away in handcuffs by uniformed police officers.
"There was no fear in the cabin at all," Kidd said in telephone interview. "It was pretty calm. Even with the frustration of having to sit there, there were no raised voices."
Passenger Karyn DiGiorgio said officers took two people off plane in handcuffs before removing the rest of the passengers. She says she was pleased with the way the situation was handled. The plane taxied on the runway for 30 minutes before the pilot told passengers that there was a "security issue," according to DiGiorgio.
The plan sat for four hours before police officers finally boarded and began removing passengers in small groups. Each passenger and his or her luggage was searched with a wand before being allowed onto an awaiting bus.
Passengers with Internet access searched the Web for details about the incident. Flight attendants admonished passengers who tried to get up and reach their overhead luggage, one passenger said. Passengers were allowed to go to the bathroom one at a time, he said.
Police eventually entered through the back door and arrested the two passengers. Others on board were taken off the plane six at a time and put on a buses.
The plane was heading to JFK International Airport in New York. American Airlines spokesman Tim Smith said there were 163 passengers and 11 crew members aboard the Boeing 767. The plane was allowed to leave SFO just before 3 p.m. without any passengers.
People who say they were aboard the plane were hitting Twitter with updates and pictures. According to some of the tweets, the plane was scheduled to take off at 7 a.m. but was delayed because of a crew member.
A passenger on board the flight tweeting as @cmckella send an update at about 12:40 p.m. that the buses were arriving at the plane to take passengers back to the terminal for security re-screening. Another tweet from @cmckella shows the scene from inside the bus as passengers were taken from the plane.
The Associated Press and Bay City News contributed to this report.