XC-99 at Kelly AFB, Texas while attached to the Military Air Transport Service 1700th Air Transport Group, 1954. Note San Antonio Air Materiel Area (SAAMA) tail marking, indicating the aircraft was assigned to the Air Materiel Command. During its operational life, the XC-99 logged over 7,400 hours total time, and transported more than 60 million pounds (27,000 metric tons) of cargo.
The XC-99 in flight with a B-36B.
Sitting in the XC-99’s cockpit, Test Mot Russell R. Rogers (left) talks with another Convair employee about flying the world’s largest land plane.
XC-99, The Cargo/Transport Version of the B-36 Only one was ever built. It was, and still is, the largest land-based, piston-engined cargo carrier in the world. The XC-99 was the biggest variant of the basic B-36 design, and became a one-of-a-kind example.
It was hoped by Consolidated Aircraft to be the first of a fleet of huge cargo/troop transports for the newly independent U. S. Air Force. It was also envisioned to be the first of a new fleet of giant “Clippers” for Pan American World Airways. But, it was not to be. However, the XC-99 did prove its worth in Air Force operational service for nearly eight years, 1949-1957.
Perhaps way ahead of its time and a precursor of the 747 “Jumbo Jet,” this enormous “Pachyderm Piston” could have ushered in the era of wide-body, supersize airliners some twenty years earlier.
Design of the XC-99 originated in the early days of the Second World War with a Consolidated Aircraft Corporation commercial land plane study designated Model 36. Model 36 was proposed only six months after the award of the XB-36 prototype contract. The May 1942 design study was based on the XB-36, utilizing the bomber’s wing, tail, powerplants, and landing gear. Consolidated figured that considerable cost savings could be made in the development of the commercial plane by advance work done on the military XB-36 sister ship, particularly in regard to the powerplants and other common parts.
A cargo/troop transport was also proposed, and the USAAF ordered one airplane SN 43-52436. Contract No. W535-AC-34454 was awarded on December 31,1942, at an estimated cost of $4.5 million, plus a fixed-fee of $180,000, with delivery to be in 21 months. The contract specified that the XC-99 project was not to interfere with construction or cause delay in delivery of the first XB-36 airplane. Work called for by the contract was to be accomplished at the government-owned plant leased to the contractor in Fort Worth, Texas. Design and development work on the plane proceeded slowly during the war, since the project had a low priority.
Model 36 was slightly smaller in size than the completed XC-99 eventually delivered to the Air Force. The wing was the same dimension, with a 230 ft. span, just like its sister ship, the XB-36 bomber. However, the 12.5 ft diameter of the military fuselage was increased to a 13.5 ft by 19.3 ft elliptical fuselage, which was to be formed by two intersecting cylindrical sections.
Fuselage length was to be 173 ft; fuselage height, 19.4 ft; horizontal stabilizer, 59 ft; height of a twin tail was 40 ft, some 17.5 ft shorter than the XC-99’s single tail. A distinctive design feature of Model 36 was the twin rudder tail also proposed for the XB-36 prototype.
The commercial fuselage was to be pressurized for high altitude flight, averaging 300 mph cruising speed at 30,000 ft. Size and capacity of the XB-36 engine turbo superchargers would have been decreased to conform with the reduced requirements of the commercial version. Gross weight was to be 265,000 Ibs.
Interior arrangements provided seats for 144 passengers in the day arrangement, which converted to 68 sleeping berths in the night arrangement. Capacity for luggage, mail, and express was approximately 12,000Ibs. Although 144 may not seem like a lot of passengers today, it should be noted that the main transport for the airlines in the early 1940s was the Douglas DC-3, which carried only 21 passengers. Even the four-engined DC-4 still carried only twice as many passengers.
The Model 36 airliner was to have a crew of five, plus a five-man relief crew for long distance flights. Also included on the airliner would be seven stewards and a nurse, presumably female.
By 1944, the Model 36 design had been further refined into Convair Model 37, and as the XC-99 military version reached its definitive form with the same six 3,000 hp Pratt & Whitney Wasp Major engines, wing and landing gear of the XB-36 prototype then under construction at the Fort Worth plant. Work on the XC-99 was also planned for Fort Worth concurrent with work on the XB-36. Around 60% of the parts would be common to both the XB-36 and XC-99. The XC-99’s huge fuselage was to be fabricated in two sections in San Diego, and the wing, powerplants, and landing gear were to be shipped from Fort Worth.
R. R. Hoover, assigned to be XC-99 Project Engineer, had worked previously on the P3YCatalina project as Assistant Project Engineer, and moved from San Diego to Fort Worth with 17 engineers in August 1942. Detail design work started, and a wooden mock-up was built in the plant’s paint shop, where the engineering was going on for the XB-36 prototype. After about 20 months, Convair asked the Army Air Forces for permission to move the XC-99 project back to San Diego. At the time of signing the contract, the San Diego plant was occupied with the engineering and development of the B-32 heavy bomber and production of B-24 Liberators. Subsequently, conditions had been reversed in 1944 and the Fort Worth plant was conducting all B-32 and B-36 production engineering. This relieved the crowded conditions at San Diego, making space available in the Experimental Shop and engineering. The Army Air Forces let Convair relocate the project back to San Diego under the following conditions: That it would not interfere with the development, testing, and delivery of the B- 32 bomber; and that the XB-36 would receive at all times higher production priority than theXC-99. All parts common to both the XB-36 andXC-99 were to be constructed at Fort Worth and shipped to San Diego for assembly into the XC-99.
Transfer of the project was completed by May 1944, and Hoover resumed with a nucleus of just seven engineers. He eventually had a staff of around 80. This was the first time a double load fuselage had ever been built, carrying such high loads. It was a challenge, and a test section of the fuselage was constructed to test various weight limits.
Portions of a wooden mock-up were built once again, mainly the flight deck and a section of the fuselage, including cargo openings. Practice loading was done with vehicles. Jeeps and halftracks were easily loaded, and it was planned to eventually handle a medium tank. One day, during ramp loading tests in the mock-up, a command car was being loaded, and at one point slipped back down the ramp, a minor embarrassment to Convair.
Model 37 would feature an extended fuselage with a length of 182.6 ft; fuselage height of 20.6 ft; horizontal stabilizer of77.2 ft, and a single tail towering 57.5 ft. Gross weight was 265,000 Ibs. The cargo/troop transport version could carry 50 tons of cargo, 400 fully-equipped troops, or 300 litter patients with their attendants. Volume of the XC-99’s fuselage was the equivalent often railroad freight cars. The largest Army Air Forces transport during World War II carried only 50 soldiers. Range was 1,720 miles with a full 100,000 Ib load of cargo, or 8,100 miles with a smaller load of 10,000 Ibs. Cruising speed was 290 mph, and with an estimated top speed of 335 mph at 30,000 ft.
Under R. R. Hoover’s supervision, as Model 37 Project Engineer, the XC-99 began to take shape in San Diego. After the wings had arrived from Fort Worth, on four railroad flat cars, they were mated with the double-deck fuselage, and the XC-99 was completed.
It hadn’t been necessary to run the R-4360-25 Wasp Major engines on test stands like Fort Worth did for the XB-36. They were proven engines by now, more or less. The engines were, however, run statically on the XC-99 when it was in the experimental yard. This jiggling of the plane, caused by engine vibrations, led to a problem of the concrete cracking beneath it. This was resolved by beefing up the apron inside the yard connecting to the heavier runway. It was a tight fit keeping off the adjacent blacktop. There were just a few taxi tests, because many of the planes’ systems had already been tested on the XB-36. It was important, of course, to check the brakes and other vital systems.
Finally, the XC-99 was ready for its maiden flight. The successful first flight was made on November 24,1947. Piloting the world’s largest land plane was Russell R. Rogers, Chief of Flight Test and Research at Convair San Diego, and Beryl A. Erickson, from the Fort Worth plant.
Rogers, age 41, soloed when he was just 15 years old. He had been a Curtiss test pilot for several years until 1932, when he took an assignment of piloting explorer Richard Archbold to the far corners of the world. Later, Rogers joined Convair, bringing over 25 years of flying experience to the Flight Test division.
Assisting Rogers was Beryl A. Erickson, who flew the XB-36 prototype on its first flight some 15 months earlier. A veteran of 16 years flying experience, Erickson was currently test flying B-36 bombers at Fort Worth.
Flight engineers on board the XC-99 were Mel Clause and B. B. Gray. L J. Bordelon and Larry Brandvig were stationed in the tail section as powerplant observers. Flight test engineers for the first flight were John T. Ready and G. W. Hofeller, who were seated right behind the two pilots. The radio operator was William C. Geopfarth. All were members of the San Diego division, except Geopfarth.
On a Sunday morning, crowds gathered atop Point Loma and high ground all over the city to watch the gigantic aircraft fly for the very first time. Traffic all around the Lindbergh Field airport area was jammed with eager sightseers. R. R. Hoover was on a microphone, making a radio broadcast of the event. He described the take off from a control tower located on the roof of a Convair building. The XC- 99s take off was slow and steady, slower than its sister ship, the XB- 36.
Airborne after a run of approximately 4,000 ft down Lindbergh’s mile and a half long runway, the flight was uneventful as the XC-99 cruised leisurely over Southern California for an hour. The second flight was made on December 2, 1947, with Russell Rogers once again at the controls. The two hour, forty minute test hop went well, as various systems were tested and procedures evaluated. Co-pilot was Phil Prophett. Hoover was aboard for this #2 flight. There were no seats on the XC- 99 except for the crew, and he had to sit on the cargo deck floor, a little behind the pilots, strapping himself in with a safety belt to the cargo tie-downs. There was no partition dividing the flight deck and cargo compartment. Hoover recalled in later years how odd it felt to be the sole passenger in the cavernous upper deck. He thought it was like, “sitting in a bowling alley, two or three lanes wide.”
The XC-99 became a familiar sight over San Diego, and of course, so did the distinctive heavy-throated sound of its engines. Convair wanted to maintain good public relations, so when the San Diego Council of Churches complained about the noise of the XC-99 disturbing Sunday church services, pilot Russell Rogers promptly changed the plane’s take off time from 11 a. m. to 1 p. m. in the afternoon, after services had concluded.
The next 18 months were spent conducting the company’s extensive flight-testing program. Phil Prophett flew the plane from the left-hand seat many times, and Hoover recalls one particular day when Prophett wandered into the experimental yard to pick up and fly the XC-99. The ground crew and engineers were still checking out the aircraft and Prophett asked, “how do things look?” Hoover told him about a couple of hours more. With that, Prophett told him that he might as well get some hours in an L-13, which was a small liaison lightplane Convair was building for the military. Hoover thought it ironic that the Convair test pilot would come off the little L-13 directly into flying the world’s biggest land plane!
The XC-99’s big, single-wheel landing gear it shared with the XB-36 was replaced with the standard four-wheel gear of the early production B-3os. Installation of the four-wheel gear in San Diego had been accelerated by a structural failure of the single-wheel landing gear installed on the YB-36, the second B-36 prototype. The XC-99 first flew with its new four-wheel landing gear on January 24,1949.
The XC-99 was flown to Forth Worth on February 11,1949, for completion of the Phase I flight test program, and to ready the plane for acceptance by the Air Force. Phase II testing was conducted by Air Materiel Command Flight Test Division at the Convair Fort Worth plant from April 23 to May 7. This testing disclosed that the airplane exceeded the guaranteed performance figures of the Model Specifications.
One of numerous XC-99 cargo/troop loading options.
A full 100,000 payload had been lifted for the first time by a Convair crew on April 15,1949, setting an unofficial world record. The previous record had been established by a Convair B-36B, operated by the 8th Air Force, with a 84,000 Ib load consisting of two 42,000 Ib dummy “Grand Slam” conventional bombs.
The XC-99 was officially delivered to the Air Force on May 26,1949. Accepting for the Air Force was Captain Robert Walling on behalf of Air Materiel Command. On one of the acceptance flights prior to delivery, Walling put the XC-99 through its paces, inluding a hair-raising dive. It was required to perform a steep dive and pullout before Air Force acceptance. The AF officer aboard for this test was scared stiff during this maneuver. Walling could tell it just by looking at him. Shortly after the XC-99 nosed over and started a screaming dive downhill, like a skyscraper plunging to earth, the pale officer declared the test “passed” as soon as he could!
But Captain Walling later laughed about the test, and personally taxied the XC-99 across the field from the Convair plant. Assigned to the 7th Bomb Wing at Carswell AFB, Texas, it was to undergo extensive inspections prior to later reassignment to another Texas base, Kelly AFB. The Air Force’s flight test program for the XC-99 was to be conducted by the 436th Bomb Squadron, which made a complete overall inspection the following month.
Maintenance of the XC-99 was the responsibility of M/SGT Howell M. Covert, a 436th Bomb Squadron crew chief, and his assistant, T/SGT C. E. Cornell. Both had just completed a seven-week familiarization training course on the XC-99 over at Convair.
R. R. Hoover was in Fort Worth when the first flight was made by an Air Force crew, piloted by Captain Dean G. Curry of the 492nd Bomb Squadron, 7th Bomb Wing. He specifically remembers this first flight. He knew the planned flight was for about an hour and twenty minutes. Weather was just a little windy, so Hoover called the Convair tower, and asked what the weather prediction was for the day. The man in the tower was a pretty good forecaster, and told him that if the XC-99 didn’t get back in 50 minutes, it would have to stay up at least an hour and a half to avoid a storm. A famous “blue-northerner” was coming through the area with 80 mph winds.
Captain Curry circled the runway and started to bring the XC-99 in for a landing with 40 mph crosswinds and gusts up to 60 mph. He crabbed the plane in the wind sideways, but managed to straighten her out over the runway just as he neared the pavement. Hoover thought it quite a feat of flying and was surprised the pilot handled the difficult landing as well as he did. The big slab-sided fuselage of the XC-99 sort of acted like giant billboards or sails, catching the wind easily.
Captain Curry accomplished a total of six landings at Carswell in the newly inspected XC-99. During the remainder of June, he logged five more flights, of which one was a night mission and one was an emergency landing at Kelly AFB, the plane’s future home.
Record-breaking flights would follow in years to come. In September 1950, the XC-99 got its orders and proceeded to Kelly AFB with a team of Convair and Air Force engineers. It was assigned to the San Antonio Air Materiel Area (SAAMA) as a project aircraft. Colonel Theodore W. Tucker, Deputy of Operations at SAAMA, was named project officer and chief pilot due to his earlier experience as a B-36 pilot. An operational test program was begun the following month to fully determine its capacity for moving heavy loads long distances at reasonable cost. Largely on the XC-99’s performance in operation would rest the Air Force’s decision to move ahead into an era of huge “super-freighters,” or remain with present operational cargo aircraft produced in greater numbers.
Loading of the XC-99 in 1950 would be considered somewhat primitive by today’s standards. The double-deck fuselage, with each level containing two cargo sections, was equipped with power hoists. Access to the lower cargo floors was through an opening in the bottom of the fuselage immediately forward of the wing, and another opening immediately forward of the tail. Hatches for loading the upper deck were located over the lower deck openings.
Mobile cargo, such as trucks, jeeps, and similar equipment, were driven up the ramps located at the lower forward and lower rear cargo openings. For weight-saving reasons, these narrow ramps were built in pairs for each opening, and permitted adjustment sideways for the various treads of vehicles. Trial loading of such equipment into a full-scale mockup was made before the XC-99 design was finalized.
It was anticipated that various other types of cargo, including packaged, crated, and barreled items, would be carried in the XC-99. Other possible cargo loads would include some non-powered wheeled equipment, requiring a winch to pull them up and down the cargo loading ramp.
These needs led to the development of specialized cargo hoists. Four hoists were installed in the XC-99, one in each cargo compartment. A number of safety features were built into the hoists to prevent their inadvertent operation during gusty flying conditions, to prevent damage to the structure, and to set the traverse brakes automatically in the event the airplane maneuvered unexpectedly.
Proposed C-99 version of the XC-99 included pressurization of the upper deck, a lengthened nose wheel to eliminate the slight forward slope of the plane, a bubble-type canopy with a new three-level flight deck; and the installation of large, clam-shell doors in the nose section.
To improve and simplify loading procedures on the XC-99, Convair proposed to the Air Force a new production version of the plane, called C-99. With this proposal, Convair entered the stiff competition in the strategic transport field, along with the Douglas C-124Aand Boeing C-97. Both aircraft had already been purchased by the Air Force.
Redesign of the C-99 was done by a Convair Fort Worth division engineering team headed by J. W. Larson, chief engineer at Fort Worth. The C-99 would have the following major changes. The newly installed six R-4360-413,500 hp engines would be replaced by a new model of the Pratt & Whitney Wasp Major, rated at more than 4,000 hp. In addition to the increased horsepower, this VDT version offered greater fuel economy, increasing the range of the C-99 (as once proposed for the B-36 bomber, this VDT engine later failed to go into actual production).
The fuselage would be redesigned to permit pressurization of the upper deck for the transport of troops and hospital cases. The lower deck would be used exclusively for cargo, and would be unpressurized. Pressurization would also enable the C-99 to operate-on return hauls-as a hospital ship, carrying 343 litters and 33 medical attendants. With cargo in the lower compartment, the C-99 could carry 183 troops in the upper compartment. Total troop capacity in both compartments would be 401 combat-ready troops with field equipment.
The nose wheel installation would be lowered so it did not protrude into the lower cargo compartment, and a lengthened nose wheel would make the cargo floors level, whereas the XC-99 had a slight forward slope. The most obvious visual changes would have been the incorporation of the bubble-type canopy of the production B-36s with a three-level flight deck, and the modification of the XC-99’s nose and tail to be equipped with integral loading ramps and clamshell doors. The new doors would provide a 12 ft by 13 ft entrance opening at each end of the XC-99. This would permit vehicles, including the largest Army tanks and USAF trailers, to be driven under their own power into the lower cargo department. On a trans-Atlantic mission, a fleet of 44 C-99s could simultaneously transport an entire U. S. Army airborne division of 17,500 troops.
It was estimated by Convair that about 70% of B-36 parts and tooling could be used in a mass production version of the C-99. Preliminary cost estimates, on this basis, would cost the Air Force about $1.5 million a copy and be competitive with the Douglas and Boeing entries on the price factor. The Air Force did not take Convair up on the C-99 proposal.
In its first seven weeks of operation as a freight carrier, the XC-99 hauled 1,114,654 Ibs of high priority cargo. This total was accomplished in five roundtrip missions out of its home base, Kelly. Missions included three flights to various military bases in the West, one to Macon, Georgia, and a record-making nonstop flight across the continent with 85,000 Ibs of air materiel.
In all, the XC-99 flew 17,182 miles on its introduction as an air freighter, ferrying military supplies a total of 602,000 ton-miles. On the transcontinental run, the XC-99 carried about twice as much freight as its nearest rival, the C-124, which required two hops for the 2,200 mile flight. Twenty-three international records for cargo flown various distances, at different altitudes, were shattered by the XC-99, including two broken on its transcontinental trip. Every flight took a lot of planning; even the temperature had to be considered. Cool air gives more lift, and more than once a trip had to postponed during the hot Texas summer.
As the evaluation program of the XC-99’s long distance weight-lifting capabilities continued, the Korean Conflict came into the picture on June 25,1950. The new war made an enormous logistic demand for movement of supplies to West Coast ports, and within days the XC-99 began its contribution. On October 10, it amazed airfreight airmen by hauling 42 badly needed C-54 engines to Me Chord AFB, Washington, in one non-stop flight from Kelly. It carried 27 of them on the lower deck and 15 on the upper. On arrival at Me Chord, the plane taxied down a perimeter strip with only one foot clearance on each side, and then backed into the loading area by reversing propellers. Me Chord airmen had never seen an airplane back up before!
In the first six months of 1951, the XC-99 underwent more modifications at Kelly AFB, sealing up fuel tanks, beefing up the main landing gear, adding another cargo door, and installation of a cargo elevator. The plane returned to service in July under the direction of Captain James M. Pittard, Jr., Project Officer. Captain Pittard was eventually to fly more hours than any other Air Force pilot in the XC-99.
In April 1952, pre-loaded cargo bins made at Kelly were added to the XC- 99 for small, high-density, high-priority items to be packed on the upper deck. This new bin arrangement allowed the top deck to be loaded in less than 30 minutes, and loading a single bin took less than 4 minutes. Each of the 13 bins loaded aboard had a cargo capacity of two tons, and total loading time for the XC-99 took a little over three hours. Gross take off weight of the XC-99, fully loaded, was now 322,000 Ibs. With a 21,116 gallon fuel capacity, the plane had a range of 8,100 miles and an operational top speed of just over 300 mph. The following data is for one month’s operation 0anuary 1952) of the XC-99 in Air Force service. Number of cargo flights, 15; hours flown, 117 hours, 15 minutes; total cargo carried, 1,123,000 Ibs; average loading time per 10,000 Ibs of cargo, 54 minutes; average man hours of off-load 10,000 Ibs of cargo, 5 hours, 54 minutes; direct flight cost per ton mile, $.29 cents.
Normal Air Force flight crew for the XC-99 included pilot, co-pilot, two flight engineers, navigator, radioman, and two rear scanners. The engineers were described by a former XC-99 commander as, “by far the most important men on the plane.” The flight engineers monitored a maze of instruments to keep the six temperamental 28 cylinder engines running smoothly. No aircrew ever had such room. There were 11 bunks, two hot plates, an electric oven, an ice box, a dining table with chairs, a food storage compartment, and a roomette-size compartment just for the aircraft commander’s relaxation.
Captain Pittard described the XC-99 as quieter and more comfortable than any other plane he had flown. Another commander, Maj. James Douglas, was less enthusiastic, saying, “I’ve flown a lot of planes and I can say definitely that the XC- 99 handled differently than any other aircraft. It was more like a B-24 than anything else. It responded slowly; you had to stay out in front of it at all times. I don’t mean to say you had to be some special kind of pilot to fly it, but you had to understand it. It never let you forget that you had 50 tons of cargo behind you.”
The XC-99 was in continuous operation from July 1951 to May 1952. It was put on a schedule and flown to the West Coast twice a week, usually to McClellan AFB, near Sacramento, California. It flew 600 hours during this period, and airlifted seven million pounds of equipment, nearly half of which was in support of the Korean effort. Captain Pittard commented in 1968, “that overseas flights of the XC-99 were not as frequent as stateside flights, but they differed little, except in planning. The XC- 99 operation after 1951 became fairly routine. We flew to McClellan and Fairchild most frequently. Other bases included Travis, Edwards, El Toro USMCAS, McChord, Stead, Hill, Rutland, Walker, Holloman, Biggs, Bergstrom, Brooks, Tinker, Carswell, Ellsworth, Wright-Patterson, Boiling, Loring, Robins, Turner, Brookley, March, Davis Monthan, Barksdale, Pensacola NAS, Charleston, Amon Carter Field, North Island NAS, and Lindbergh Field.”
Captain Pittard noted that the XC-99 reached the 1,000 hour flying mark in July 1952. He also commented on three overseas flights:
Mission to Ramey AFB, PuertoRico-ThefirstXC-99flighttoRameyAFBoccured in December 1950. Captain Pittard had started flying as co-pilot in the XC-99 two months earlier in October. After the first trip to Ramey, in which he did not fly, the XC-99 returned many times to the sultry Caribbean base. After Captain Pittard was checked out as 1st pilot in 1951, he flew as many as two missions a month to Ramey. On a typical Ramey flight, the XC-99 took off at midnight and flew over the gulf direct to Key West, Florida, and then straight to Puerto Rico. The flight was about 11 hours long, and the payload was around 75,000 Ibs. Departure from Ramey AFB usually was early the following day with a return cargo load.
Mission to Rhein Main, West Germany – Captain Pittard was the aircraft commander on the trip. The XC-99 departed Kelly AFB about 04:00 hours on August 12,1953, and after a three leg flight, arrived in Germany on August 14. Cargo payload was 62,000 Ibs; kept relatively low due to carrying additional fuel to counter possible headwinds flying to Europe. Returning with a cargo load, the flight back to Kelly took 35 hours, accomplished in three hops.
The XC-99 flew more hours than any other Air Force experimental aircraft. It could fly more cargo further and cheaper than any other airplane in history. But its very capacity frustrated all efforts to give the go-ahead for production models. It could haul cargo for $.16 cents per ton mile, compared to $.26 cents for other smaller military cargo-carrying aircraft already in the inventory. The problem was that for a trip to be a financial success, the XC-99 had to carry nearly a full cargo load from Kelly AFB to its destination, and then find at least a 60,000 Ib load waiting for the return trip. There simply was no cargo route, at the time, which could provide that much tonnage.
XC-99 flights were canceled in March 1957, and the evaluation program came to a quiet end. SAAMA maintenance at Kelly estimated that nearly 145,000 man-hours and one million dollars would be needed to replace structural sections that had reached limitation by the patch and reinforcement method, undergo essential modifications, and other general repair for its return to service. An impressive total of 7,400 flying hours on its frame had taken its toll. It had been flown 1,486,000 miles by aircrews at Kelly.
The XC-99 was grounded. There was the possibility it would wind up on the scrapheap. Former crewmen, Air Force historians, and San Antonians all protested a scrapping. While proposals for preservation were made, the XC-99 languished in a quiet corner of Kelly. Serious consideration was given to flying it to Dayton, Ohio, and placing it in the Air Force Museum collection. The idea was abandoned because of the expense of putting it in flyable condition for just one flight. Also, Dayton had no building, at that time, able to house the XC-99.
Crew: 5 (with a relief crew of 5)
Capacity: up to 400 troops / 100,000 lb (45,000 kg) cargo
Length: 182 ft 6 in (55.63 m)
Wingspan: 230 ft 0 in (70.10 m)
Height: 57 ft 6 in (17.53 m)
Wing area: 4,772 sq ft (443.3 m2)
Airfoil: root: NACA 63(420)-422; tip: NACA 63(420)-517
Empty weight: 135,232 lb (61,340 kg)
Gross weight: 265,000 lb (120,202 kg)
Max takeoff weight: 320,000 lb (145,150 kg)
Fuel capacity: 19,112 US gal (15,914 imp gal; 72,350 l)
Powerplant: 6 × Pratt & Whitney R-4360-41 Wasp Major 28-cylinder air-cooled radial piston engine, 3,500 hp (2,600 kW) each
Propellers: 3-bladed Curtiss-Electric constant-speed fully-feathering pusher propellers
Maximum speed: 307 mph (494 km/h, 267 kn)
Range: 8,100 mi (13,000 km, 7,000 nmi) with 19,112 US gal (15,914 imp gal; 72,350 l) and 10,000 lb (4,500 kg) payload