Helicopter Sikorsky S-55 Serial 55-771 Register HS-5 used by Royal Thai Air Force. Built 1954. Aircraft history and location Aircraft History For HS-5 see also mi-8ps 133 05 HS-5 Royal Thai Air Force 1954-10-21Sikorsky S-55 c/n 55-771, ff:? del RTAF as HS-5, 21Oct54. HS3-5/97 Send Updates Use APP to upload photo @ (optional) When Now? / / Send