Security fears caused the cancellation of a BA flight to Washington, 24 hours after a plane on the same route was detained for a lengthy search.
Passengers were held for three hours on a flight with the same number on Wednesday
Flight BA223 was due to leave London Heathrow for the US capital at 1505 GMT on Thursday.
But it was cancelled before passengers could board after talks between BA security and the UK Government.
Flight BA223 on Wednesday was held for three hours on the tarmac at Washington while US agents questioned passengers.
The 180 passengers due to board Thursday's flight were transferred to other flights.
It has emerged that F-16 fighter jets escorted Wednesday's BA flight and that one Aeromexico flight from Mexico City to Los Angeles was cancelled on Wednesday because of security concerns.
BBC correspondent in Washington, Jon Leyne, said the fears of a possible attack appear to be based on suspicious names on passenger lists, and information that specific flights may have been targeted.
"We had concerns with individuals on the flight, but threat reporting
information led us to make the decision to have [Wednesday's] flight escorted," a
national security official said.
"It was fact-related," the official said, and not just connected to the
passenger list the US now receives from airlines flying to the US.
Wednesday's BA223 was held in an area well away from the main terminal building, while officials from the FBI and the Transportation Security Agency boarded the plane.
Federal Bureau of Investigation spokeswoman Debbie Wierman said some of the passengers "were folks that law enforcement officers were interested in speaking with."
But it was described as "routine" questioning with no one arrested.
It was over three hours before passengers were ferried to the arrivals building.
The US has raised its national alert status to orange - the second-highest level - and six Air France flights to Los Angeles were cancelled last week.
A BA spokesman said the airline was still hoping to operate Friday afternoon's flight to Washington but a firm decision would be taken in the morning.
He said he did not know whether the advice which prompted the
cancellation of Thursday's flight was terrorist related.
"We were only told that it was for security concerns, that's all, and we
complied fully with their requests," he said.