A U.S. Air Force instructor pilot died of his injuries Tuesday after the ejection seat of his plane mistakenly activated during ground operations at Sheppard Air Force Base in Texas, officials say. The instructor, Captain John Robertson, was in a T-6A Texan II at Sheppard Air Force Base in Wichita Falls, Texas when the ejection seat was activated. Robertson was severely injured and succumbed to his injuries on Tuesday. “This is a devastating loss for Captain Robertson’s family and loved ones, and for the entire 80th Flying Training Wing,” said Col. Mitchell J. Cok, the acting wing commander. “…