 By 2006, aircraft upset accidents had overtaken CFIT as the leading cause of aircraft accident fatalities, credited to the widespread deployment of TAWS.On March 7, 2006, the NTSB called on the FAA to require all U.S.-registered turbine-powered helicopters certified to carry at least 6 passengers to be equipped with a terrain awareness and warning system.The technology had not yet been developed for the unique flight characteristics of helicopters in 2000.