National Transportation Safety Board Chairman Deborah A.P. Hersman speaks during an investigative hearing in Washington on Wednesday, Dec. 11, 2013, into the crash landing of Asiana Airlines Flight 214 in San Francisco in July. (AP Photo/Jacquelyn Martin)
National Transportation Safety Board Chairwoman Deborah Hersman calls Thursday for a probe of the government agency charged with ensuring the safety of tour buses, saying its own look into four crashes that killed 25 people raises "serious questions" about how well the agency is doing its job. (Associated press)
** FILE ** This photo provided by the National Transportation Safety Board, shows the wreckage of a helicopter that crashed near Mosby, Mo., on Aug. 26, 2011. The pilot of an emergency medical helicopter may have been distracted by text messages when he failed to refuel his helicopter and misjudged how far he could fly before running out of fuel. (AP Photo/NTSB)