After temporarily reinstating the flight numbers for the flights that crashed into the World Trade Center and at Shankville, Pennsylvania on September 11, 2001, United Airlines apologized, blaming it on a technical error, "We apologize for the error. The numbers were inadvertently reinstated."

Flight 93, which departed Newark for San Francisco, crashed at Shanksville, killing 44 people, and Flight 175, from Boston to Los Angeles, crashed into the WTC South Tower, killing 65 on board. While United had stopped using the flight numbers after 9/11, the numbers went back into use on Monday night. According to the AP, "A notice posted Tuesday on the airline schedule website said United planned to reactivate the two flight numbers Saturday, but that Continental Airlines [now part of United] would operate the flights in a code-sharing arrangement. A code share allows one airline to book seats on a flight operated by a second airline. Often the flights operate with the name of the airline that did the booking rather than the airline operating flight."

The numbers are now being taken out of the system. The head of the Association of Flight Attendants said, "Out of respect for those who lost their lives and those who will always remember our heroes, United Airlines must what should have already been done —- immediately and permanently retire these flight numbers," while the Air Line Pilots Association said, "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."