At a public hearing yesterday, the NTSB singled out Part 91 operations in a special study on helicopter and fixed-wing EMS accidents. Between 1994 and 2004, the number of accidents doubled, with 83 since 1998. Main accident causes are CFIT, inadvertent operation into IMC and spatial disorientation or lack of situational awareness in night operations. Though citing many factors, the NTSB pointed to less stringent requirements of Part 91 when no patients or organs are on board, as opposed to Part 135. Of the 55 most recent accidents, 35 occurred under Part 91 repositioning flights. The hearing culminated in the release of four recommendations to the FAA: require all EMS flights to comply with Part 135 when medical personnel are onboard; mandate that all EMS operators develop flight-risk evaluation programs; require the use of flight-following procedures that include a dispatcher; and mandate the installation of terrain warning systems on all EMS aircraft.