 After a spike in air ambulance crashes in the United States in the 1990s, the U.S. government and the Commission on Air Medical Transportation Systems (CAMTS) stepped up the accreditation and air ambulance flight requirements, ensuring that all pilots, personnel, and aircraft meet much higher standards than previously required.The resulting CAMTS accreditation, which applies only in the United States, includes the requirement for an air ambulance company to own and operate its own aircraft.Some air ambulance companies, realizing it is virtually impossible to have the correct medicalized aircraft for every mission, instead charter aircraft based on the mission-specific requirements.