“I would not have chosen to make this mistake,” Williams said in the interview with the military newspaper.  “I don’t know what screwed up in my mind that caused me to conflate one aircraft with another.” He also posted an apology on his Facebook page and offered similar sentiments during Wednesday night’s broadcast of “Nightly News.” The Iraqi incident took place before Williams took over the “Nightly News” anchor desk from Tom Brokaw in 2004.

What makes Williams’ admission worse, according to one person familiar with the situation, is that he had been counseled in the past by senior NBC News executives to stop telling the story in public. The advice, this person said, was not heeded.  One person familiar with current NBC News operations disputed that information.

Williams’ version of the story has never been allowed in NBC News programs, according to three people familiar with the unit. Indeed, in a March, 2003, episode of “Dateline,” Williams described the helicopter trip accurately. “On the ground, we learned the Chinook ahead of us was almost blown out of the sky,” he said while narrating a report.