The acting chief of the Transportation Security Administration yesterday defended his agency’s practice of allowing the more than 1 million ground employees at U.S. airports to bypass security checkpoints that screen for weapons. Under sharp questioning from members of a congressional panel, David M. Stone said the TSA relies on employee identity badges that are provided after background checks. “We place a heavy emphasis on background checks . . . rather than the guns, gates and guards approach,” Stone told the House aviation subcommittee. Stone was testifying at a hearing called to examine the TSA’s plan to enhance airport security by conducting vast computerized background checks on passengers. Full Story