CHICAGO United Airlines (UAL.N) temporarily revived the flight numbers of two hijacked planes used in the September 11 attacks but said on Wednesday the move was inadvertent and they would not be used.
"We are taking immediate steps to remove them and apologize for the error," a United spokesman said.
Call numbers 93 and 175 were mistakenly assigned to two flights by Continental Airlines, which has merged with United.
United declined to explain how the numbers found their way back onto flights. Unionized flight attendants urged the company to permanently retire them, while pilots said the move was insensitive.
Flight 175, a Boeing 767, took off from Boston and was one of two planes flown into New York's World Trade Center.
Flight 93, a Boeing 757, took off from New Jersey's Newark International Airport and crashed into a Pennsylvania field. Investigators believed the hijackers of that plane wanted to hit the U.S. Capitol or the White House.
Two other planes used in the attack were flown by American Airlines. Flight 11, a 767 from Boston, hit the World Trade Center, and Flight 77 from Washington Dulles, crashed into the Pentagon.
AMR Corp AMR.N, parent of American Airlines, long ago retired those two flight numbers.
Other airlines, however, continue to use all four of the numbers for their flights.
(Reporting by Kyle Peterson and John Crawley)