last flight occurred in 1988. Although the ducted fan propellers were considered usable, they were not used again on a US military aircraft until the F-35B. Surviving aircraft Although not on display, the only currently remaining craft, 151521, is currently stored by the Niagara Aerospace Museum, New York. According to the employees at the Museum, the craft was held onto after being debated for scrapping by the Navy. Specifications (X-22A) See also References Citations Bibliography Apostolo, Giorgio. The Illustrated Encyclopedia of Helicopters. New York: Bonanza Books, 1984. . "Bell-X22A: Analysis of a VTOL research vehicle." Flight International, 23 March 1967, p. 445. Markman, Steve and Bill Holder. Straight Up: A History of Vertical Flight. Atglen, Pennsylvania: Schiffer Publishing, 2000. . Rogers, Mike. VTOL: Military Research Aircraft. New York: Orion Books, 1989. . External links aerospaceweb.org X-22 Tilting ducted fan aircraft X-22, Bell Four-engined tractor aircraft Tandem-wing aircraft Turboshaft-powered aircraft Aircraft first flown in 1966