 These pressure changes require advanced knowledge by flight staff with respect to the specifics of aviation medicine, including changes in physiology and the behaviour of gases.There are a large variety of helicopter makes that are used for the civilian HEMS models.The commonly used types are the Bell 206, 407, and 429, Eurocopter AS350, BK117, EC130, EC135, EC145, and the Agusta Westland 109, 169 & 139, MD Explorer and Sikorsky S-76.