At a public hearing last month, the NTSB singled out allegedly less safe Part 91 operations in a special study on helicopter and fixed-wing EMS accidents. EMS aircraft must operate under Part 135 when carrying patients, passengers and organs, but may fly under Part 91 when only authorized crewmembers are on board. Between 1994 and 2004, the number of EMS accidents doubled. Main causes are CFIT, inadvertent operation into IMC and spatial disorientation or lack of situational awareness in night operations.