UPDATE: US Airways has cleared up some of the confusion around how the image was posted.
According to a spokesperson for the company, US Airways was attempting to flag an inappropriate tweet that contained the graphic image. In doing so, the pic.twitter.com URL was copied, as well. Then the graphic image was inadvertently pasted into a tweet sent to another user. While the two tweets were live they actually linked to each other. The airline’s spokesperson said they’re very sorry for what happened and that it was an honest mistake.