HMX-1’s perfect seventy-four-year safety record ended seven seconds later. Dead level and flying at two hundred and thirty-seven miles per hour, twenty-six-thousand pounds of helicopter flew into the Frederick, Maryland, Walmart Supercenter’s front entrance. If the helicopter had flown a single foot lower, it might have averted the disaster that unfolded. By less than three inches, the Superhawk cleared the three-foot-high concrete bollards lined across the entrance to keep a truck from driving into the entrance as part of a burglary attempt. The VH-92A Superhawk blew through the glass doors, its fifty-six-foot-diameter, four-blade rotor killing twenty-seven people at the checkout kiosks and another nine at the Subway sandwich deli to the side as the blades shattered. It plowed throug