The forward fuselage is fully pressurized and provides space for 5 to 8 crew and up to 28 passengers, but the cargo space is pressurized to only 3.55 PSI / 0.245 bar allowing for a lighter airframe. A door equipped with pressure bulkhead is located at frame 14, separating the cargo attendant's compartment from the main cargo compartment. This allows the rear cargo doors to be opened during flight for paratroops and equipment drop. Like the An-12, the aircraft has a circular fuselage section. The An-22 has set a number of payload and payload-to-height world records. The An-22 has the general appearance of an enlarged version of the earlier Antonov An-12 except that it is fitted with a twin tail. This gives the An-22 better engine-out performance, and reduces height restrictions for hangars. Also of note are large anti-flutter masses on the top of each tail. Only one production variant was built, the standard An-22. Prototypes, such as the one first featured at the 1965 Paris Air Show had fully glazed noses that lacked the nose-mounted radar of production models. Those aircraft had the radar mounted below the right wheel well fairing, forward of the wheels. Antonov designated a variant with a modified electrical system and an additional augmented flight control system the An-22A but the designation was not used by the military. A proposed civil airliner version capable of seating 724 passengers on upper and lower decks was planned but wasn't constructed. (For comparison, a typical Boeing 747 can carry 400–500 passengers.) Several other An-22 variants were projected and constructed by Antonov but never entered serial production, notably a nuclear-powered aircraft and a ballistic missile platform. The An-22 was originally built for the Soviet Air Force and Aeroflot (the state airline). Rearming from An-12 in the Air Force began in July 1974. Several Military Transport Aviation units were equipped. The 12th Mginsk Red Banner Military Transport Aviation Division (based at Migalovo) was one of the units which had its three regiments entirely equipped with the An-22s. Another unit that operated it was the 566th Solnechnogorsk Military Transport Aviation Regiment, which used the An-22 from 1970 to 1987. An early use of the An-22 was to deliver Soviet humanitarian aid to Peru in July 1970 following the Ancash earthquake. One An-22 disappeared on 18 July during these relief flights.