Convair XC - 99 The Convair XC - 99 , AF Ser . No . " 43 - 52436 " , was a prototype heavy cargo aircraft built by Convair for the United States Air Force . It was the largest piston - engined land - based transport aircraft ever built , and was developed from the B - 36 bomber , sharing the wings and some other structures with it . The first flight was on 23 November 1947 in San Diego , California , and after testing it was delivered to the Air Force on 23 November 1949 . Design and development . Design capacity of the XC - 99 was of cargo or 400 fully equipped troops on its double cargo decks . A cargo lift was installed for easier loading . The engines face rearward in a pusher configuration . Operational history . In July 1950 the XC - 99 flew its first cargo mission , " Operation Elephant . " It transported of cargo , including engines and propellers for the B - 36 , from San Diego to Kelly Air Force Base in San Antonio , Texas , a record it would later break when it lifted from an airfield at elevation . In August 1953 , the XC - 99 would make its longest flight , , to Rhein - Main Air Base , Germany , by way of Bermuda and the Azores . It carried more than each way . It attracted much attention everywhere it flew . The US Air Force determined that it had no need for such a large , long - range transport at that time , and no more were ordered . The sole XC - 99 served until 1957 , including much use during the Korean War . It made twice weekly trips from Kelly AFB to the aircraft depot at McClellan AFB , California , transporting supplies and parts for the B - 36 bomber while returning by way of other bases or depots making pick - ups and deliveries along the way . During its operational life the XC - 99 logged over 7 , 400 hours total time , and transported more than 60 , 000 , 000 lbs of cargo . The aircraft made its last flight on 19 March 1957 , landing at Kelly Air Force Base , where it would remain for the next 47 years . The then - United States Air Force Museum at Wright - Patterson AFB in Dayton , Ohio , requested that the aircraft be flown there for display , but the Air Force refused due to the $ 7 , 400 cost of the flight . Retirement and display . Late 1950s and 1960s . The aircraft was put on display at Kelly Air Force Base near San Antonio , Texas , in 1957 . During the 1960s , it was considered for restoration by the San Antonio Air Logistics Center at Kelly AFB , but the deterioration of the airframe due to the high magnesium content led to the abandonment of that plan . The aircraft was later moved to a grassy field near the base . 1990s . In 1993 , the USAF moved it back to the Kelly AFB tarmac ( 29°22 ' 27 . 19 " N 98°35 ' 14 . 37 " W ) . It was planned to move the XC - 99 by road to the National Museum of the United States Air Force at Wright - Patterson Air Force Base , Ohio , restore and reassemble it , and put it on display in the USAF Museum ' s collection of experimental aircraft . Ultimately , transporting the massive aircraft by ground proved impractical and too expensive . Base Realignment and Closure ( BRAC ) action in 1995 resulted in the partial closure and realignment of Kelly AFB , with most of the former San Antonio Air Logistics Center becoming civilianized and renamed Kelly USA , while the runway and those flight line areas supporting C - 5 and F - 16 flight operations of the Air Force Reserve Command ' s 433d Airlift Wing and the Texas Air National Guard ' s 149th Fighter Wing reverted to adjacent Lackland AFB and renamed Lackland AFB / Kelly Field Annex . 2000s . Disassembly of the aircraft began at Kelly Field in April 2004 . Portions of the airframe were then airlifted from Kelly to Wright - Patterson Air Force Base near Dayton , Ohio . Transporting the XC - 99 components taxed the C - 5A ' s cargo capacity , as the largest piece moved intact was over 75 feet by 13 ft . Upon arrival at Wright - Patterson ' s active base , the parts had to be further moved by truck several miles to the museum side of the base . By the summer of 2008 , the XC - 99 had been completely transferred to Dayton and was lying on the ramp outside the museum ' s restoration facility ( ) . Upon examination , the aircraft was found to have suffered from considerable corrosion , which was not unexpected considering it had remained outside for over 50 years . The wing spar was found to be too badly corroded to restore , and a new replacement would need to be fabricated . A full restoration is being performed by the restoration crew of the Air Force Museum , although no timetable existed at the time . 2010s . As of May 2011 , the corrosion control of the center wing boxes was nearing completion . Once this portion of the project is finished , the XC - 99 will be reassembled and the restoration work started . Following restoration , the aircraft was expected to be displayed inside in one of the museum ' s new hangars . Like its relative the B - 36 , it is expected to become a showpiece of the museum . Once all aircraft have been moved from the Museum ' s current " Research and Development Hangar " or " Presidential Hangar " to a new display hangar planned to be added onto the main Museum buildings , the XC - 99 restoration project will move into the vacated hangar , where visitors will be able to watch the restoration in progress . Upon completion , the XC - 99 will remain on display in either the former R & D hangar , or Presidential Hangar . Pending the restoration and display of the XC - 99 , in an effort to educate visitors about the aircraft the Air Force Museum has placed a model of the XC - 99 on display in its Post - Cold War Gallery . The model , in approximately 1 / 72 scale , was constructed by Lt Col Howard T . Meek ( USAF , Ret ) a member of the museum ' s restoration staff . An explanation of the Museum ' s plans for the restoration and display of the XC - 99 is located in the case with the model . Recent developments . Because the XC - 99 arrived in worse condition than had been expected the magnitude of the restoration was greater than the restoration staff was able to quickly accommodate . During the seven - plus years the aircraft has remained exposed to the elements at the Wright - Patterson Air Force Base it has continued to deteriorate . In an effort to protect the aircraft , in the summer of 2011 , a decision was made by the restoration staff to move the disassembled XC - 99 to the 309th Aerospace Maintenance and Regeneration Group ( AMARG ) storage facility at Davis – Monthan Air Force Base , in Tucson , Arizona . The XC - 99 will remain at Davis – Monthan Air Force Base , in an area containing other aircraft belonging to the Museum , until the restoration staff has the time and resources to perform a full restoration . Current situation . Although this article contains a number of references to information about the XC - 99 at the website of the National Museum of the USAF , which were apparently valid between May and September 2011 , those references are no longer valid 6 months later on 2012 - 03 - 11 . The aircraft is no longer listed as a restoration project or tour destination at the Museum , as the references suggest , and the factsheet about the aircraft no longer exists . Indeed a search for the aircraft at that website using ' XC 99 ' produces only 3 finds , 2 of which are links to the non - existent factsheet about the aircraft . Currently few links at the website of the National Museum of the USAF confirm that the aircraft was once a restoration project at the museum . From the previous section a decision appears to have been taken in 2011 to return the dismantled aircraft to the south - western USA ( it passed 47 years at the Kelly Air Force Base in San Antonio , Texas , before being moved to the Museum in Ohio ) , this time to the Davis – Monthan Air Force Base , in Tucson , Arizona ( the dry conditions of the Arizona desert would protect the aircraft from further corrosion until a full restoration can be carried out or until its deterioration can be otherwise prevented ) . It is not clear whether the dismantled aircraft has , in fact , been moved to Davis – Monthan ; whether it remains at the National Museum of the USAF at Wright - Patterson ; or indeed whether it has been moved elsewhere . As of 2012 - 03 - 11 this article requires fully up - to - date information about the current status of the aircraft . On 12 April 2012 , the XC - 99 in very poor condition , was still at Wright Field outside of the restoration hangar . By 31 May 2012 , the 337th Airlift Squadron moved the tail assembly and the propellers to Davis – Monthan Air Force Base , Arizona . Planned civil variant . The Convair Model 37 was a large civil passenger design derived from the XC - 99 but was never built . The Model 37 was to be of similar proportions to the XC - 99 ; length , wingspan , and a high - capacity , double - deck fuselage . The projected passenger load was to be 204 , and the effective range . Fifteen aircraft were ordered by Pan American for transatlantic service . However , the fuel and oil consumption of the six Wasp Major radials powering the XC - 99 and B - 36 meant that the design was not economically viable , and the hoped - for turboprop powerplants did not materialize fast enough . The low number of orders were not sufficient to initiate production , and the project was abandoned .