United Airlines apologizes for recycling 9/11 flight numbers

United Airlines is apologizing Thursday for briefly reusing the flight numbers of its planes that were hijacked by terrorists on Sept. 11, 2001. 

United had assigned flights 93 and 175 to flights on Continental Airlines, which it merged with last year. After being criticized by the flight attendants and pilots unions, United said quickly that the numbers were assigned by mistake. 

"We regret these flight numbers were inadvertently reinstated," United said it a statement it also tweeted. "We apologize and are taking immediate steps to remove them."

On 9/11, United Flight 175 took off from Boston's Logan Airport, heading for Los Angeles, Calif. But it was crashed into the south tower of the World Trade Center in New York. An American Airlines flight was flown into the other tower.

Around the same time, United 93 departed from Newark International Airport in New Jersey en route for San Francisco. It was believed to be heading for a target in Washington after being hijacked by terrorists, but passengers aboard the plane fought back for control of the aircraft and it crashed in a field in Pennsylvania. 

With that history in mind, the union that represents flight attendants, the Association of Flight Attendants-CWA, said Thursday that the flight numbers should be banned forever. 

"September 11, 2001 forever changed our airline and our country," AFA President Greg Davidowitch said in a statement. "Everything changed that day and we will never forget the heroic actions of our friends and colleagues or the pain of their loss.

“We have advised United Airlines that reinstatement of flights 93 and 175 is a terrible misstep. Out of respect for those who lost their lives and those who will always remember our heroes, United Airlines must do what should have already been done - immediately and permanently retire these flight numbers.”

The Air Line Pilots Association, International agreed, calling the flight numbers being reassigned "reprehensible." 

“The thought of anyone among management at United Airlines to even consider reinstating these two sacred flight numbers – on the heels of Osama bin Laden’s death – demonstrates a severe disconnect from right and wrong,” United Master Executive Council Chairman Captain Wendy Morse said in a statement. 

“Their insensitivity and unconscionable disrespect of these sacred flight numbers and their meaning to the employees of United Airlines and the families of those who lost their lives nearly 10 years ago are not only alarming, but reprehensible," Morse continued. “How could these flight numbers have been ‘inadvertently reinstated’ as the company indicates? The pilots of United Airlines expect accountability of how these flight numbers were considered in the first place.”

United attributed the mix-up to a computer error.

This story was corrected May 20 at 9:48 a.m. from an earlier version