prototype crashed during a precautionary landing resulting from loss of gearbox oil pressure, only the Navigator/ radio operator surviving. After joining the flight test programme the second prototype began a series of world record breaking altitude/payload flights for turbine powered helicopters. State acceptance trials were passed successfully in 1961, but production did not commence until 5 March 1964 at the Rostov-on-Don factory, with first flight of a production aircraft on 10 September 1964, leading to a total of forty of the long-legged Mi-10 helicopters built, from 1964 to 1969. An early production Mil Mi-10 was exhibited in western Europe for the first time at the June 1965 Paris Air Show at Le Bourget Airport. Mi-10K (short legged version) The limitations of the Mi-10 in the slung load mission soon became obvious, chiefly, the loss of payload due to the heavy and complicated undercarriage, and more importantly the almost complete lack of oversight of the slung load, despite the inclusion of a CCTV (closed circuit television) system intended for observation of slung loads. Foregoing the requirement to carry palleted or podded cargoes, Mil redesigned the Mi-10 with a much shorter, fixed, four-leg undercarriage and replaced the extendible escape chute with a gondola fitted with flying controls for a pilot to fly the aircraft during slung load operations. The remainder of the aircraft is essentially identical with the long-legged version. Seventeen of the new flying crane were produced as the Mi-10K, including two conversions from Mi-10s from 23 March 1974 to 1977. Operational service The operational service of the Mi-10 was of moderate success, being distributed mainly to units of the VVS (Voyenno-Vozdushnyye Sily - Soviet Air Force) which already operated the Mi-6. Operations with no load were found to be unstable, and the best procedure for take-off was found to be a rolling take-off, which usually also resulted in nose-wheel shimmy when lightly loaded. The main mission of the early Mi-10 virtually evaporated with the improvements in contemporary ballistic missiles; thus the majority of the long-legged variants were converted to Mi-10PP, (or mi-10P), airborne Electronic Counter-Measures helicopters, carrying a large ST-900 Step' (Step''' - Steppe) ECM pod under the fuselage mounted on a pallet. Other Mi-10 long legged aircraft were converted to carry out a wide variety of missions but usually only as single prototypes. Of special note was the Mi-10R (R - - record) record breaking helicopter, converted from a