The pilot made an emergency landing in Manchester, England, about 160 miles short of London, because the Boeing 747 ran low on fuel Feb. 19 after facing headwinds that were stronger than expected, the Federal Aviation Administration said.
The FAA and British aviation officials are investigating the flight to determine whether any regulations were violated.
"We are concerned," said Laura Brown, an FAA spokeswoman.
The decision not to return Flight 268 after the engine lost power raised concerns about a new European Union law which requires European carriers to reimburse passengers for substantial delays.
U.S. officials said they have no evidence the airline's decision to continue on was influenced by the regulation.
"We would never compromise the safety of our passengers," said British Airways spokeswoman Diane Fung on Monday. "The plane is certified to fly on three engines. It is perfectly safe to do so. The pilots are trained for such situations.
Flight 268 was carrying 351 passengers.