The Boeing Model 307 Stratoliner (or Strato-Clipper in Pan American service, or C-75 in USAAF service) is an American stressed-skin four-engine low-wing tailwheel monoplane airliner derived from the B-17 Flying Fortress bomber, which entered commercial service in July 1940. It was the first airliner in revenue service with a pressurized cabin, which, along with supercharged engines, allowed it to cruise above the weather. As such it represented a major advance over contemporaries, with a cruising speed of 220mph (350km/h) at 20,000ft (6,100m) compared to the Douglas DC-3's 160mph (260km/h), at 8,000ft (2,400m) then in service.[4] When it entered commercial service it had a crew of five to six, including two pilots, a flight engineer, two flight attendants, and an optional navigator and had a capacity for 33 passengers, which later modifications increased, first to 38, and eventually to 60.
Boeing S-307 Stratoliner production line, with early B-17s to the rearPrototype Model 307 NX19901 with the small tail as initially designed, and which caused its loss
In 1935, Pan American Airways, United Airlines, American Airlines, Eastern Air Lines, and Transcontinental & Western Air (T&WA) had each signed a contract with Douglas to develop the forty-passenger DC-4 (later known as the DC-4E).[5] Each company contributed $100,000[notes 1] to development costs and agreed to not operate other aircraft with a maximum weight of 43,000 to 75,000lb (20,000 to 34,000kg) for revenue service.[5] Due to development problems and poor performance, all of the airlines dropped out of the DC-4 program and cancelled their orders, but a requirement for a large four-engine airliner remained.[6][7]
Donald Webb Tomlinson at T&WA carried out five years of high altitude flight research, with a Northrop Gamma and a Douglas DC-1, which helped determine that T&WA would need a four-engine airliner with a pressurized cabin.[8] During this period, he also test-flew the XB-17 and determined that it would provide an ideal basis for an airliner, and so Boeing was approached with the idea.[7] A ceiling of at least 16,000ft (4,900m) was required both to avoid summertime "chop" over the Rocky Mountains and to allow the aircraft to fly around the thunderstorms that can sometimes block mountain passes, which meant a pressurized cabin would be the most comfortable for passengers on long flights.[9] In 1935, Boeing then designed a four-engine airliner using components from the Boeing Model 299 B-17 Flying Fortress heavy bomber as the Model 307. It combined the wings, tail, rudder, undercarriage, and engines from the B-17 with a new, much larger pressurized circular–cross-section fuselage with a maximum diameter of 138in (3.5m).[10]
The pressurization system required extensive testing, which was carried out over many months, progressively increasing the air pressure after each successful test, and each time, the highly polished fuselage was coated with soapy water while the fuselage was pressurized, for workers to look for the bubbles that would indicate a leak, much like testing a bicycle inner tube.[11]
Before the first aircraft had rolled out, T&WA's chief engineer discovered that the extruded metal tubing used for the wing spars was defective, with stress corrosion cracks produced by cold rolling the tubing to increase tensile strength.[9] Affected aircraft included the prototype, the first Pan Am machine, and some early production B-17s, and this resulted in T&WA having to have their engineers inspect every tube that was to be incorporated into their aircraft.[9]
Wreck of the prototype, NX19901
The first aircraft completed, registrationNX19901, crashed on March 18, 1939,[12] while being demonstrated after having been recently fitted with instruments to measure flight control forces.[13] The Boeing 307 took off at 1257hrs (local time) from Boeing Field in Seattle with ten occupants,[13] and they climbed to an altitude of 11,000ft (3,400m), where stability tests were made and, while carrying out side-slips near Alder, the aircraft stalled and entered a spin.[13] It made two to three turns before the pilot was able to stop the spin using the engines,[12] however, the ensuing high-speed dive and the forces that resulted from attempting to pull up before hitting the ground resulted in the left outer wing tearing off with one engine still attached, followed by the right wing, just outside the outer engine, both of which also tore off parts of the tail as a result of the aileron cables pulling them against the fuselage, which then caused the aircraft to pancake into a forested area at 1317hrs.[3][14] All ten aboard were killed,[14] which included T&WA's representative, KLM's technical director, a Dutch Air Ministry representative, and Boeing's test pilot, their Chief Aerodynamicist, and their Chief Engineer.[12] Parachutes were available but the force of the spin prevented their use.[3]
The crash delayed the program by over a year, beginning with a three-month investigation by the US Civil Aeronautics Authority, the precursor to the current Federal Aviation Administration, and Boeing to determine the causes.[3] Flight and wind tunnel testing showed that both an extended dorsal fin and an enlarged vertical tail were needed to prevent the rudder stalling in a yaw, and solutions were flight-tested on NC19903, including an intermediate solution consisting of just an extended dorsal fin.[15] The resulting redesign was also incorporated into the redesign of the rear fuselage of the B-17E bomber.[16] The wings were reinforced and Handley Page slots were added to the outer wing leading edges to improve low-speed aileron control while the inboard flaps were also extended.[3][14] The first several aircraft, including NC19902, NC19903, and NC19904, were all rolled out with the small tail and then modified later.
Test flights resumed on May 19, 1939, after the changes had been incorporated,[14] and on June 20, 1939, the first flight was made with the "supercharged cabin" pressurization system on.[6]
On March 13, 1940, Approved Type Certificate (ATC) number 719 was assigned to the Pan Am Boeing 307s, allowing commercial deliveries to commence.[6] A second ATC was issued for the T&WA aircraft, number 726, due to the numerous differences between the Pan Am and the T&WA aircraft.[17]
TWA Boeing SA-307B NC19905 on May 17, 1940, after the engines iced up and it made a forced landing
T&WA was concerned about excessive undercarriage stiffness from their experience with the test flights with the XB-17, which were to be modified for the airliner.[7] T&WA flight-tested the modified undercarriage and in hard landings easily exceeded the contract's minimum required 500ft/m (46m/ft) descent rate with a successful 800ft/m (74m/ft) landing descent.[18]
T&WA was also concerned about the engine carburetor intake heaters being deliberately restricted by Boeing to prevent cooking the engines, which could potentially leave crews unable to clear ice.[19] Their point was made when icing problems during a test flight on May 17, 1940, with NC19905, while carrying dignitaries in overcast conditions over mountains resulted in three of the four engines failing, while the fourth was losing power, despite every measure being taken to clear the ice. This resulted in the aircraft making a belly landing in a field with a partially lowered undercarriage,[19] just south of Lamar, Colorado.[20] T&WA then modified the carburetor heating themselves and the aircraft was repaired and returned to service.[19]
Boeing made claims both in their period advertising and in their current web site that it was the first high-altitude commercial transport and the first with a flight engineer.[21] However, its first flight, on December 31, 1938, was later than that of the Renard R-35, which also had a pressurized cabin for passengers and flew on April 1, 1938, but that craft crashed and its development was abandoned.[22] As for employing a flight engineer, it was preceded in the US on a commercial aircraft by Maddux Air LinesFord Trimotors, whose "Mate" had the same responsibilities as a flight engineer.[23] Additionally, all German World War OneRiesenflugzeug multi-engine bombers had flight engineers as they were integral to the specification.[24]
Design
TWA Boeing SA-307B NC19907, Zuni, fleet number 402, landing with slotted flaps lowered, prewarPan Am Boeing S-307 Stratoliner NC19902 Clipper Rainbow with blanking plates installed on engines to prevent engine over-cooling
As built, the Stratoliner used the all-metal stressed-skin cantilever wings from the B-17C mounted low on the fuselage to a constant-chord center section faired to the fuselage,[25][26] with four 1,100hp (820kW)Wright GR-1820 Cyclone air-cooled radial engines. TWA examples used GR-1820-G105A engines fitted with two-stage superchargers for high-altitude performance, while the Pan Am examples used the GR-1820-G102 with a single-stage supercharger.[25][27][28] To reduce noise, engine exhaust collector rings and mufflers were installed.[29] TWA aircraft were fitted with cowl flaps, to adjust engine cooling air, while Pan Am aircraft had fixed cowling rings without cowling gills.[27] When operating in cooler conditions, the Pan Am aircraft could be fitted with blanking disks that partially covered the fronts of the engines. Both versions had sufficient power to maintain altitude on only two engines,[28] one of the KLM requirements.[30] Both used three-bladed Hamilton Standard Hydromatic constant-speed propellers,[26] and new high-octane fuels were developed to help the engines operate under the increased supercharger pressure.[31] Both versions had trailing-edge flaps controlled with electric motors,[8] although the SA-307B, for T&WA, and the SB-307B, for Hughes, featured slotted flaps with prominent external hinges, while the Pan Am examples had simpler split flaps with flush hinges, similar to those used on the B-17s.[27][23] All of the fuel was carried in the wings, with, in each wing, a 212.5USgal (804L; 176.9impgal) tank between the inboard nacelle and the fuselage, a 425USgal (1,610L; 354impgal) main tank, and a 212.5USgal (804L; 176.9impgal) tank between the inner and outer nacelles, making a total capacity of 1,700USgal (6,400L; 1,400impgal) in six tanks.[27] With the fuselage being 3.5ft (1.1m) wider than that of the B-17, the span had increased from 103ft 9in (31.62m) to 107ft 3in (32.69m) compared to early B-17s.[11] After being modified, the SA-307B-1s used the wings and elevators from the B-17G, with split flaps, and 1,200hp (890kW) Cyclones.[26] On most, but not all, examples, the leading edges of the wings, horizontal stabilizer, and fin were fitted with rubber expanding-type de-icing boots, which would inflate and deflate repeatedly to break ice from the flying surfaces.[26] All movable surfaces, including the rudder, ailerons, and elevators had fabric over metal structures and were aerodynamically balanced and fitted with adjustable trim tabs to lighten flight loads.[26][29] The rudder and elevators also had hydraulic boost to lighten control forces.[27] The partially retractable main undercarriage had hydraulic brakes, used Goodyear 55×19×23 tires, and was raised and lowered with electric motors.[26] Manual backups were provided for electrically driven systems, but the power had to be turned off before being used.[32] A parking brake was provided, along with an emergency air brake system run off a bottle of compressed air, while the tailwheel was fully retractable.[26][33]
Passengers on Pan Am Strato-Clipper in the Raymond Loewy-designed interior. Seats on the left could be folded into sleeper bunks.
The fuselage was described as being dirigible-shaped and was an elongated teardrop, with a 11.5ft (3.5m) constant-diameter tube lengthening it at its widest point.[28][34] The circular-section fuselage was of all-metal construction, skinned with 24ST Alclad[26][27] and capable of maintaining a cabin pressure equivalent to 8,000ft (2,400m) when flying at a 16,000ft (4,900m) altitude and 12,000ft (3,700m) when at 20,000ft (6,100m),[9] with a maximum pressure difference of 2.5lb/sqft (12kg/m2).[31] The structure was designed with strength reserves so as to handle as much as 6lb/sqft (29kg/m2), but a pressure relief valve prevented the pressure difference from exceeding 2.65lb/sqft (12.9kg/m2).[34][35] The structure consisted of continuous longitudinal stiffeners spaced every nine degrees around the fuselage with radial hoop stiffeners mounted every 16in (410mm) along the fuselage, reinforcing the similarity to a dirigible.[36] The skin seams were sealed with tape impregnated with sealing compound trapped between lapped joints which were secured with two rows of rivets spaced 5⁄8in (16mm) apart, while doors and hatches were sealed with soft rubber gaskets and control cables entered the pressurized cabin through specially developed glands designed to allow free movement of the cables with a negligible amount of air leakage.[34] The main cockpit windows were made from 5⁄8in (16mm) thick la glass, while the rest of the windows were made of Plexiglass or Lucite sealed into rubber channels.[34] A large ram-air scoop on the cabin roof was provided to supply cooling air while at lower altitudes, and it was shut off when the cabin was pressurized at higher altitudes.[27] The cockpit was fitted with an autopilot, radios,[26] and a radio direction finder (RDF) for navigation.[37]
The industrial designer Raymond Loewy designed the passenger cabin, with furnishings provided by Marshall Field's.[28] It was divided into four compartments, each with six deep comfortable reclining chairs which could be converted into 16 sleeping berths.[26][38] Each compartment was provided with adjustable air conditioning vents, reading lights, and a call button.[38] Nine additional seats were provided along the port side of the aircraft, while washrooms which doubled as dressing rooms were provided at both ends of the cabin.[26] The rear washroom was for women and was named the Ladies’ Charm Room. Its walls were covered in heavy plate-glass mirrors, and it contained in its 34sqft (3.2m2) area two dressing tables, each with a sink, plush upholstered stools, soft indirect lighting provided by fluorescent lamps, ashtrays, hot and cold running water, shelves with towels, and a separate cubicle for the toilet.[8][38] The men's washroom was in front as the Men's Lounge and also had a separate cubicle for the toilet, two sinks, and outlets to run electric razors.[8] A galley of just 28sqft (2.6m2) providing hot food was situated at the rear of the cabin,[26][38] behind which was positioned the rear hemispherical pressure bulkhead.[34] Up to 412cuft (11.7m3) or 6,590lb (2,990kg) of baggage could be stowed under the floor of the cabin, both between the wing spars and behind the rear spar, and it was accessible in flight, through a hatch in the cabin floor, or on the ground through three hatches on the underside of the fuselage.[34][38] Extensive use was made of the latest in soundproofing, and the Dynafocal engine shock mounts were designed to reduce vibrations felt by passengers.[8][33] The air-conditioning system used both electrical and mechanical approaches,[29] with a vent in the leading edge of each wing near the root to bring outside air to two engine-driven superchargers that compressed the air, which was then passed through radiator condensers to cool the air, and it was then run through channels to the vents in the cabin.[29] External hookups allowed ground air conditioner units to cool the cabin air when the engines were off.[29]
Crew
Newly graduated Hostesses lined up in front of Zuni, TWA's Stratoliner NC19907, in early to mid-1940
The Stratoliner was normally flown with a pilot and co-pilot, and both Pan Am and T&WA aircraft carried a flight engineer to reduce the workload on the two pilots by monitoring the engines for any problems and fine tuning them, while they also controlled fuel consumption from each of the tanks to maintain the aircraft's fore–aft and lateral balance. Too much fuel used in one tank could result in the aircraft becoming uncontrollable. They also monitored other aircraft systems, including hydraulics and the cabin pressurization system.[39] The flight engineer was also an aircraft maintenance engineer (AME) and, aside from operating the radio, which required training in Morse code, he was also responsible for all technical issues and would carry out repairs and maintenance on the 307.[23] Each Pan Am aircraft had one additional crew member compared to T&WA aircraft: Because they made long overwater flights, they carried a navigator, who was not yet considered necessary by the CAA for overland flights, which were served by a network of beacons across the continent[39] when the aircraft were not being flown by visual flight rules (VFR).
Both T&WA and Pan Am normally carried two flight attendants on each aircraft. T&WA began using Hostesses, as they called them, as cabin crew in late 1935, while Pan Am continued to use male stewards until late in WW2.[40]
C-75 conversion
42-88623 Cherokee loading up following conversion to C-75 standard
Following the entry of the United States into World War II in December 1941, long-range transports were needed to ferry government and military officials around the globe and many aircraft, including T&WA's Boeing 307s, were pressed into service. Beginning in February 1942, these were flown to Albuquerque, New Mexico for conversion, which included the removal of the plush, but heavy, civilian fittings, including the massive mirrors in the women's "charm room", and the pressurization system, to save weight.[41] The sound insulation was also stripped out leaving the cabin much noisier than it had been.[42] The forward (men's) washroom and the forward two of the four passenger compartments were replaced with five gravity-fed 212.5USgal (804L; 176.9impgal) fuel tanks and a 45USgal (170L; 37impgal) oil tank fed with a wobble pump, along with a rest area for the crew.[41][43] A desk was added behind the pilot for a radio operator, who had a 50-watt Bendix TA-12 high-frequency Morse transmitter and a BC-348 tunable receiver. A 400ft (120m) trailing wire antenna was used with a 5lb (2.3kg) lead weight on the end–which the radio operator needed to remember to reel in, by hand, when landing. Inexperience sometimes led to the antenna either being torn off or lashing against the fuselage. An astrodome was fitted and the Perspex top windows, which produced excessive parallax, were replaced with optically flat glass to allow the navigator to compare the positions of stars to the horizon to determine latitude when crossing large bodies of water.[41] The SA-307B-1s retained the astrodomes when converted back from C-75 in 1944. To further aid navigation, a B-3 driftmeter was installed along with an aperiodic compass that did not lag or lead in turns as a conventional compass does.[41]Mae West life vests and life rafts were also provided.[41]
The landing gear was strengthened, and the maximum takeoff weight was increased from 45,000 to 56,000lb (20,000 to 25,000kg), leaving the Stratoliner underpowered, and the climb suffered accordingly.[10][44][45] The overloading burnt out engines and destroyed piston rings, but closely monitoring engine oil consumption often caught failures before they occurred.[42]
Passenger facilities were reduced to four bunks which when folded away allowed seating for twelve, along with four seats along the opposite side of the aircraft.[41] Removable tables were provided in the cabin to lay out maps and do paperwork.[42] The exterior was then camouflaged in standard USAAF colours, with olive drab upper surfaces and neutral grey undersides,[10][45] and each aircraft had its name painted on the nose and over the cabin door, which would also be used by many later operators.[45] The names had previously been used in TWA publicity but not painted on the aircraft.[8]
After three years the USAAF had amassed sufficient long-range transports that it no longer needed the C-75s, and they sold the fleet back to TWA, who paid to have them converted back to civil standard under Boeing's SA-307B-1 designation. CAA concerns over cracks in the wing spar tubing led to the TWA Stratoliners getting new B-17G wings and horizontal stabilizers, with the leading edge of the longer-span, narrower-chord horizontal stabilizers[46] moved about 3ft (0.91m) aft,[47] while more powerful versions of the same Wright Cyclone engines increased power from 1,100 to 1,200hp (820 to 890kW),[47] but without the B-17G's turbosuperchargers. New propellers and landing gear were also installed.[48] The change to the tailplane required that the structural bulkhead supporting the forward spar be moved aft, while the rear bulkhead was reworked and additional fuselage stiffeners were added.[33] The tailwheel switched to using B-17G wheels and 26" smooth-tread tires, which required that the wheel well be enlarged and structure supporting the tailwheel reinforced.[33] The main undercarriage wheels, tires, tubes, and brakes remained unchanged, although the legs themselves were strengthened.[33] The fuselages were stripped to bare metal and rewired with a 24VDC 1800 amp system from the B-29 Superfortress, replacing the original 24VDC 800 amp system.[47] Maximum weight was increased to 54,000lb (24,000kg) and the maximum landing weight rose to 47,000lb (21,000kg).[49] Slots were re-incorporated into the wingtip leading edges[46] as they had been with the pre-war airliners. The cabin was redesigned and passenger capacity was increased from 33 to 38,[46][50] with the cabin divided into a 10-seat front section and a 28-seat rear section, with no sleepers.[49] The cabin pressurization system was never re-installed.[46][47] The B-17G wings came with turbo-supercharger ducting for the engines that was not needed for the simpler supercharger installation used on the Stratoliner, while one duct opening was retained on each wing between the engine nacelles to provide additional cabin air.[48] Further mods made by TWA included improved soundproofing and temperature control,[49] and on March 15, 1945, the B-1 recertification tests were completed to the CAA's satisfaction.[49] The estimated cost to repurchase and refurbish the five aircraft was $2 million.[notes 2][49]
Variants
Prototype of the S-307, with the small tail used initially on the first three examples built
300
Original unpressurized 35,200lb (16,000kg) proposal, with seating for 16–24 passengers, which began as a four-engined Boeing 247.[5][51]
Ex-Pan Am Inter-American Inc. Boeing S-307 Strato-Clipper N19903 after returning to the US from Haiti, before being bought by the SmithsonianT&WA Boeing SA-307B Cherokee as built
PAA-307 or S-307 Strato-Clipper
Designation for three aircraft built for Pan Am under ATC 719.[17] Visible external differences included engine cowlings without cowl flaps.[52] Four 1,100hp (820kW)Wright GR-1820-G102A Cyclone engines were fitted, with single-speed superchargers.[27][53] Crew of six.[1]Strato-Clipper was Pan Am's name for the type.[1]
SA-307B
Designation for five aircraft built for T&WA under ATC 726.[17] These differed externally from the Pan Am aircraft in having large external flap actuators.[52] Four 1,100hp (820kW) Wright GR-1820-G105A Cyclone engines were fitted, with two-speed superchargers.[28] Crew of five.[28]
SB-307B
Designation for one uncertified aircraft built for Howard Hughes.[17]
C-75
Five Trans World SA-307Bs were impressed into the USAAF. The cabin pressurization was removed to save weight and the external flap actuators replaced.
SA-307B-1
The C-75s were overhauled and updated with modified B-17G wings (with 307 wing slots) and larger tailplanes mounted further aft.[54]1,200hp (890kW) Wright GR-1820-G205A Cyclone engines were fitted,[26] along with B-29 electrical systems.
307C
50-passenger development with more powerful versions of the same Cyclone engines, boosted to 1,350hp (1,010kW). Boeing wanted $267,230 + 13,000 per engine (or $319,230[notes 3]) but development was cancelled in favour of the 377 Stratocruiser, based on the B-29.[47]
316
Airliner project developed from the XB-15 with pressurized cabin similar to that used on the Stratoliners, offered to KLM as a larger Stratoliner but not followed through with.[55]
322
Development of 307 with similar fuselage but with a mid-mounted wing and a nosewheel, as a bomber. Eventually evolved into the B-29.
Operational history
Ten 307s were built. NC19906 was temporarily marked as NX1940 and NC1940 for publicity purposes.[56]
Boeing 307 prototype from above, showing the wing and tail planform
The first Boeing 307 Stratoliner, serial 1994, registration NX19901, made its first flight from Boeing Field, near Seattle, on December 31, 1938, prior to its intended delivery to Pan Am following testing and certification.[58] As related above, it crashed on a test flight on March 18, 1939, killing all ten occupants, and forced several design changes, of which the fin and rudder are the most immediately obvious.
Koninklijke Luchtvaart Maatschappij N.V. (KLM)
KLM was considering four-engine airliners for the European routes and a longer-ranged four-engine aircraft for their routes to the Netherlands East Indies (now Indonesia). Aircraft considered included the Douglas DC-4(E), the Boeing 307, the Junkers Ju 90, the Focke-Wulf Fw 200 Condor, and the Bloch 160, of which only the DC-4 and 307 came close to meeting requirements.[55]
Boeing made a proposal to KLM on September 20, 1936, for an exclusive option on 10 certified 307s for $2.4 million[notes 4] with options for 18 aircraft and with first delivery in 14 months.[59] By January 14, 1937, the price had increased for 18 aircraft to $265,000 each, not including pressurization equipment.[59] KLM let Boeing know that they were interested in four aircraft, for use as an interim measure pending a larger, more suitable design, and they that they would use it for familiarization training with four-engine aircraft.[30] They required that it fly on just two engines, use Pratt & Whitney automatic mixture controls, have a 2,500mi (4,000km) range, be able to carry freight or mail, and have moderate tire ground pressure.[30] KLM then requested a quote for three 307s, with either Wright Cyclones or Pratt & Whitney 1830 engines, fitted with constant-speed propellers and automatic carburettor mixture control and with additional fuel capacity to provide a range of 3,400mi (5,500km).[55] Boeing responded that the price for three aircraft would be $289,000 each if fitted with Cyclone engines and $314,000 if fitted with R-1830s, plus $3,100–$4,000 per aircraft to increase fuel capacity to either 1,700USgal (6,400L; 1,400impgal) or 2,125USgal (8,040L; 1,769impgal), provided that the US Government gave permission to export the engines.[55] After not hearing back, Boeing sent a new quote to KLM for $300,000 per aircraft, or $320,000 for the pressurized version.[55] December 20, 1938, the KLM board made the decision to order two four-engine aircraft, with consideration of the Boeing 307 and Focke Wulf Fw 200 Condor; however, the Condor was not suitable for the East Indies route.[13]
Following T&WA defaulting on payments, the first three T&WA aircraft were offered to KLM in late 1939, but a quick decision was needed by Saturday, March 18, 1939. KLM was unable to make that decision before the offer expired and requested an extension.[13] On March 21, 1939, KLM confirmed that they still planned to buy 307s and insisted that they were content with Boeing's progress.[6] Ultimately, though, KLM did not buy the 307s because their representatives' test-flight insurance coverage was rejected, and KLM found Boeing's response to providing for the next of kin unsatisfactory, a disagreement that was not cleared up until after World War II.[6] The insurance coverage on the aircraft was sufficiently large that it had the insurance industry worried about fallout, and, as was the norm at the time, neither passengers nor crew could get coverage from any insurance company, but the aircraft itself was covered for a replacement cost of $500,000, with hull coverage and passenger liability, carried by Aero Insurance Underwriters and Associated Aviation Underwriters, despite the fact that Boeing was offering to sell the aircraft to KLM for much less than that.[60]
Australian National Airways (ANA)
Another company that Boeing was in discussions with was Australian National Airways, who they quoted $310,000 per Stratoliner, or $340,000 for a pressurized version, on July 27, 1938,[55] but nothing came of these discussions and ANA never operated the type.
Howard Hughes and Cosmic Muffin
Howard Hughes's SB-307B after conversion into The "Flying Penthouse"
The first customer delivery was to millionaire Howard Hughes on July 13, 1939.[6] He bought aircraft serial number 1997,[61] registered as NX19904, for $315,000[notes 5][62] for a round-the-world flight, hoping to break his own record of 91 hours 14 minutes set between July 10 and 14 in 1938 in a Lockheed Model 14 Super Electra. Hughes' Stratoliner was fitted with extra fuel tanks and was ready for the first leg of the round-the-world attempt when Nazi Germany invaded Poland on September 1, 1939, causing the attempt to be cancelled.[8] Hughes' aircraft was stored in Glendale, California for the duration of the war, prior to being converted into a flying condo.[63] Hughes had the extra fuel tanks removed and, for around $250,000,[notes 6] had it fitted with much more powerful Wright R-2600 engines for its transformation into "The Flying Penthouse", which included a bedroom, two bathrooms, a galley, and a bar as well as a living room.[63] In 1949, Hughes spent an additional $100,000[notes 7] renovating it so he could sell it, which, like the T&WA and Pan Am aircraft, then included an interior designed by Raymond Loewy.[62] Oil tycoon Glenn McCarthy bought it to coincide with the opening of his new Shamrock Hotel, renamed it Shamrock, and had it repainted; however, McCarthy defaulted on payments and it was returned to Hughes.[62] It languished unflown until August 1965, when it was damaged beyond repair by Hurricane Cleo, with only about 500 hours on the airframe.[64] It was then bought for $69 by Kenneth W. London, who cut the damaged wings and tail off, built a hull under it, and installed a pair of V-8 engines to convert it into a houseboat which he named Londonaire.[65] After various repossessions, deaths, and failed sales, it became the Cosmic Muffin, in which form it survives.
Transcontinental & Western Air (T&WA or TWA)
TWA Boeing SA-307B NC19905, Comanche underside, showing the 11.5ft (3.5m) fuselage width. The external arms for the slotted flaps are visible, as are the hatches on the underside providing access to the baggage hold.
As one of the companies sponsoring the development of the Douglas DC-4, Transcontinental & Western Air lost interest due to delays and poor performance, but the agreement they signed with Douglas limited the maximum weight of any replacement design to 43,000 pounds (20,000kg).[30] After discussing their needs with Boeing, T&WA signed a contract with Boeing to buy six 307s with an option for 13 more for $1,590,000 on January 29, 1937, with deliveries to be made in mid-1938.[9] T&WA defaulted on their payments, though, and the T&WA markings which had already been applied to their airframes were removed.[11] T&WA filed a lawsuit against Boeing for default of contract, and Boeing sued T&WA for breach of contract over the non-payment.[3] Hughes had begun secretly buying up T&WA shares[66] and, by March 1939, Hughes had a controlling interest in Trans-World Airlines (or TWA, as it was rebranded once he had taken over), with roughly 46% of the shares.[3] By August 1939, TWA and Boeing had resumed negotiations, and TWA would get five 307s, and Hughes would get one.[3] The cost to TWA had risen and was then $1,750,000,[notes 8] or $350,000[notes 9] per aircraft–three times the cost for Douglas DC-3s.[8] In early 1940, Hughes bought up all remaining outstanding TWA shares not otherwise reserved for employees.[3]
TWA received its first Stratoliner on May 6, 1940, and the last of their five was delivered on June 4, 1940.[56][67] It was not their first four-engine airliner, as one of their parent companies, Western Air Express, had operated the Fokker F-32. All five were named in TWA promotional material for North American Indigenous tribes–names that would be used throughout their careers, continuing long after they left TWA. War intervened in December 1941, and civil aircraft production was halted, preventing any further deliveries.[68][69] The date chosen for TWA’s first service flight was July 8, 1940, to coincide with the anniversary of TAT's 48-hour coast-to-coast service, in which trains were used for night legs.[2] TWA's Stratoliners flew between Los Angeles and New York, making three stops.
TWA's Burbank–La Guardia flight via Chicago was two hours quicker than with a DC-3 (13:40 east and 15:38 west) with three stops in each direction.[2] The main route was La Guardia, New York, to Chicago, Illinois, to Kansas City, Missouri, to Albuquerque, New Mexico, to Burbank, California, and the reverse.[2]
1940 was the best year for TWA, with a 50% increase in passenger traffic over 1939, but they were still running exclusively in the red.[32]
On September 9, 1940, a TWA Stratoliner from Chicago to New York set a commercial speed record flying the 778mi (1,252km) in two hours and fifty-two minutes at an average speed of 271.4mph (436.8km/h).[70] A few weeks later, on September 26, a TWA Stratoliner bound for New York, at 17,000ft (5,200m), with a jetstream providing a strong tailwind, reached a ground speed of 387mph (623km/h).[71]
Flight 45 added stops at Philadelphia and Pittsburgh on December 1, 1940.[73]
TWA ICD Wartime operations
C/N
Old TWA registration
Name
USAAF serial
Also marked as
1996
NC19905
Comanche
42-88624
288624
1998
NC19906
Cherokee
42-88623
288623
1999
NC19907
Zuni
42-88625
288625
2000
NC19908
Apache
42-88626
288626
2001
NC19909
Navajo
42-88627
288627
On December 14, 1941, representatives from various airlines as well as the Air Transport Association of America (ATA) met with Colonel Robert Olds of the Air Corps Ferrying Command (later renamed Air Transport Command) over the use of their airliners in wartime.[74] Pan Am had already signed a contract on the 13th, in which it would keep its 307s but sell the 314s to the government.[74] T&WA sold all five of its 307s to the USAAF but would then operate them on behalf of the USAAF on a cost-plus basis through a new subsidiary.[74] At the time the Stratoliner was the only available landplane transport capable of transatlantic flights with any payload. Seaplanes were too slow and not numerous enough, while the Douglas C-54 Skymaster would not enter service until March 1942 and took months to be available in any numbers. Aside from a few ad-hoc conversions from Consolidated B-24 Liberator bombers, the Consolidated C-87 Liberator Express would not be ready until September 1942, and the Lockheed C-69 Constellation would not fly until January 1943, while two-engine aircraft were considered unsafe for ocean crossings with VIPs aboard.[74]
On the entry of the United States into World War II, Pan Am continued operating its Stratoliners on routes to Central and South America, but under direction of the Army Air Forces' Air Transport Command.[74] All five TWA Stratoliners were withdrawn from operations on December 24, 1941, while TWA created a subsidiary, the Intercontinental Division (ICD), whose civilian crews would operate them on behalf of the United States Army Air Forces.[43]Otis Bryan was made head of the ICD.[41] The Stratoliners were sold to the USAAF, who assigned the type the C-75 designation, and each of them was given a USAAF serial number.[43] The first of these was accepted by the USAAF on March 1, 1941, and the last on December 17, 1942.[43] ICD crews included pilots, first & second officers, navigators, flight engineers, flight radio operators, and pursers.[75] ICD Supervisor pilots and captains were paid $1100/month,[notes 20] first officers $800/month,[notes 21] Navigators $600/month,[notes 22] Flight Engineers (FEs) $500/month,[notes 23] and Flight Radio Operators (FROs) $400/month.[notes 24][45] Personnel were issued USAAF uniforms, which they wore with rank stripes (two solid stripes for a captain) but with civilian insignia.[45]
USAAF C-75 42-88624 Comanche in wartime camouflage
ICD service began on February 26, when a 307 flew south to Brazil from Washington, before crossing the South Atlantic to Africa, and north to Cairo, before continuing on to Prestwick, Scotland, where they arrived on April 20, 1942,[43] having primarily carried 25,000 rounds of armour-piercing shells to British troops in Cairo, who were facing Rommel and his Afrika Corps.[76] The ICD was initially set up at the crowded Washington Bolling Field but soon transferred all of their operations to nearby Washington National Airport.[77] Passengers continued to be loaded at Bolling Field, after the aircraft flew the short hop from Washington National Airport.[78]
The first North Atlantic crossing was in March 1942, when a flight from Washington to Prestwick carried senior military and government officials including the Army Chief of Staff General George C. Marshall, General Dwight D. Eisenhower (to command Operation Torch for the invasion of North Africa), Deputy Chief of Staff of Army Ground Forces General Mark W. Clark, Operation Torch Air Force liaison officer Colonel Hoyt Vandenberg, Chief of the Navy's Bureau of Aeronautics Rear Admiral John Henry Towers, who oversaw Navy aircraft procurement and training, and presidential advisors W. Averell Harriman and Harry Hopkins, who were crossing to negotiate the Lend-Lease program.[76] From April 22, regular crossings were being made[43] and the ICD was growing rapidly, from 71 personnel in January to 343 by April, and they were then making sixteen ocean crossings a month.[77] Following his April 1942 raid on Tokyo, but before it had been made public, Jimmy Doolittle took a C-75 from Karachi, then in India, through Khartoum, Kano, and Accra to Robertsfield Airport, crossed the Atlantic to Natal, Brazil, and headed north to Belém and, from there, with an additional fuel stop, flew to Washington, D.C., arriving in time for the news of the raid to be made public.[44] Many of the surviving members of the raid followed soon after in another Stratoliner.[44]
The North Atlantic ferry route was set up with help from former Arctic explorer Colonel Bernt Balchen, who assisted with Bluie East Two and Bluie East Eight in Greenland to reduce the length of the Gander-to-Prestwick leg.[77] The first aircraft to land at these fields, which were north of the Arctic Circle, was an ICD C-75, on April 20, 1942.[77]
The exiled (but not yet deposed) King Peter II of Yugoslavia was flown in July 1942 from London[42] to Washington to meet with North American leaders, with the air–fuel mixture so lean that numerous stops could be skipped, and when the craft arrived in Washington it had been airborne for 21 hours 16 minutes through the trip.[79]
Boeing C-75 ICD primary wartime transatlantic routes after July 1942, when the airfield at Ascension Island shortened the South Atlantic crossing. Bluie Two and Eight were added in 1942 as diversionary airfields in case excessive headwinds were encountered in the North Atlantic. When conditions allowed it, usually on summer eastbound crossings, direct flights were sometimes made between Gander and Prestwick.
On July 10, 1942, Ascension Island's airfield opened in the South Atlantic,[79] shortening the hazardous transatlantic leg enough that smaller aircraft could make the crossing, and the ICD C-75s would routinely lead flights of USAAF twin-engined aircraft, such as Douglas A-20s, across.[79]
Two main routes were flown, between Washington, D.C., and Cairo across the South Atlantic, and between New York and Prestwick, Scotland, across the North Atlantic.[82] They often flew non-stop the 2,122mi (3,415km) between Gander, Newfoundland and Prestwick, Scotland in the north, and the 2,500mi (4,100km) between Natal, Brazil, and Accra, Ghana, in the south. After July 1942 a refueling stop at Ascension Island was added in the South Atlantic.[83] In the north, stops in Iceland or Greenland were often necessary when flying west against unusually strong prevailing winds. As Douglas C-54 Skymasters took over the Gander–Prestwick route, the C-75s operated between Marrakech and Prestwick over the Atlantic.[82]
The ICD C-75 crews crossing the Atlantic had to be careful to avoid Allied convoys and German U-boats to avoid being shot at.[84]Cherokee, carrying returning American troops from Reykjavik to Gander at 1,000ft (300m), was shot at by a US Navy ship that left over 200 holes in the aircraft's tail and nearly severed the elevator controls.[84] Many transatlantic trips were made at night so the navigators could get good star sightings.[76]
By 1944 the USAAF had enough long-range transports that it no longer needed the small number of C-75s it had, and it sold the fleet back to TWA, with the aircraft being transferred between January 6, 1944, and December 19, 1944.[10][56] On August 11, 1942, the ICD had received the first of 12 C-54s,[79] and Pan Am would also supplement their Stratoliners with 12 C-54s.[79] TWA received two C-54s in August and had five by September and a full allotment of 12 by November, along with the first three C-87s, to supplement the C-75s.[85] At the same time Curtiss C-46 Commandos and Douglas C-47s and C-53s provided feeder links to the C-75s, C-54s and C-87s, as their range was inadequate for the Atlantic.[85]
By the time they were withdrawn, over 3000 trans-oceanic crossings had been made,[25] and they had flown 21,284 while in USAAF service with the ICD.[47] The sole accident occurred during a night landing at Natal when an undercarriage leg was torn off by a mound of dirt.[47]
It cost TWA about $2 million[notes 25] to have the five aircraft rebuilt by Boeing, and the first of them resumed passenger service on April 1, 1945. The CAA recertified these as SA-307B-1 civilian airliners with their original registration numbers.
TWA post-war service and disposal
TWA Boeing SA-307B-1 N19909 Navajo, fleet number 404, as it appeared when offering coach-class seating only, showing the rearward location of the higher-aspect-ratio B-17G tailplane, whose hinges were then aligned with the rudder hinge
On April 1, 1945, the first post-war civil commercial flight was made by Zuni, as an SA-307B-1, from La Guardia to San Francisco via Pittsburgh, Saint Louis, Kansas City, Albuquerque, and Burbank,[49] but the second transcontinental flight did not happen until a month later, when on May 1, 1945, a flight was made from Washington, DC to Spokane, Washington, via Dayton Municipal Airport, St Louis, Kansas City, Albuquerque, and Burbank, reflected a loosening of the tightly controlled government access to routes.[86] TWA's fare structure remained the same as pre-war.[86] New TWA flight routes were added, with routes 370 & 371, between La Guardia and Spokane through Chicago, Albuquerque, for fuel, and Burbank, and routes 48 & 49, between La Guardia and Kansas City through St Louis.[86] At this time the TWA Stratoliner was briefly the sole four-engine commercial airliner in domestic service in the US.[86]
On July 10, 1939, TWA had signed a contract with Lockheed to develop the Constellation, which was to be capable of five miles/min (350mph, 560km/h), compared to the Stratoliner's four miles/min (246mph, 396km/h),[8] but, with production diverted to military for the duration of the war, the first TWA Constellations did not enter service until February 1946, and they were soon grounded, dealing with the usual teething problems encountered with a new type, from July 11 to September 20, 1946, while the Douglas DC-4s began arriving in 1946 in small numbers and, similarly, the Douglas DC-6 from 1947.[86] In May 1949, due to strong competition from non-scheduled flights using cheaply purchased war-surplus Douglas C-54s, the Stratoliners were downgraded to a coach-only service with the fares slashed by a third.[87] The first coach service, from New York La Guardia to Chicago via Pittsburgh, was made on June 1, 1949, with a full load of 38 passengers.[88]
In November 1950, TWA introduced the similarly sized but cheaper-to-operate twin-engine Martin 2-0-2A on domestic routes[89] and transferred some DC-4s from international routes to domestic service,[87] supplementing the Stratoliners, which were mainly being used for service between La Guardia and cities in the Midwest,[46] until TWA finally phased them out between April and July 1951.[90] At that time the aircraft had an average of 25,205 hours flying time each, with Cherokee having the most at 26,324 hours,[87] and they had covered 7,500,000mi (12,100,000km) while in ICD service.[48]
In 1937 Pan American Airways placed their first order for two Stratoliners, which they soon increased to six. Deliveries to Pan Am started in March 1940,[67] and they had received their first three before war intervened and civil aircraft production halted.[68][69] The other three would not be built.[3] All three were named for historically notable Clipper ships. Pan Am carried out their first revenue flight on July 4, 1940,[2] with service between Miami, Brownsville, Texas, and Los Angeles.[67] Unlike TWA, Pan Am did not exclusively assign their aircraft to specific routes, and instead they were used for their Latin American routes and ranged from Miami and Los Angeles to Brazil.
Aerovias Ecuatorianas C.A. (AREA) Boeing S-307 Strato-Clipper HC 004
When TWA's Stratoliners were getting new wings and tails, Pan Am's 307s were being modified in Miami to repair the cracked spar tubing with doublers and did not get new wings or engines; the maximum gross weight remained the same.[63] Pan-Am flights then resumed between Miami, the Caribbean, and Belém,[51] until all three were sold to the Airline Training Company of Miami in late 1948 and early 1949,[64] before being sold on to other operators.
The former Clipper Comet NC19910 was sold to Aerovias Ecuatorianas (AREA) in Ecuador, in 1951, who used it as Quito with the registration HC 004 to provide service between Ecuador and Miami. From 1955, it was with Quaker City Airways for two years as N75385, making non-scheduled charter flights.[91] On May 10, 1958, while still carrying the same registration and after having been stored for some time, it was being readied to be ferried to Boeing for modification for use as a crop duster, but flight tests were carried out despite finding fuel leaks whose source could not be determined, and with untested auxiliary fuel tanks installed in the cabin. During the flight test, it caught fire, and while the crew landed it safely on a boulder-strewn mesa and escaped unharmed, the airframe was destroyed by the fire.[64][92]
The former Clipper Rainbow NC19902 was to have been sold to the short-lived Mercury Airways of South Africa and was even given the South African registration ZS-BWU. However, the sale was never completed, and, similarly, it was supposed to have been sold to Aerovias Ecuatorianas, with registration HC-SJC-003, but that sale also appears to have fallen through. In 1951 it was sold to Aigle Azur as F-BHHR.[93]
The former Clipper Flying Cloud NC19903 was purchased by the Haitian Air Force (French: Corps d’Aviation d’Garde d’Haïti) in 1954 and assigned the number 2003, but plans to use it for a passenger service by the Compagnie Haïtienne de Transports Aériens (CoHaTA) were cancelled and it was fitted out as a presidential transport. When François "Papa Doc" Duvalier came into power in 1957 he chose not to use it and instead had the aircraft sold the same year, with the money from the sale going toward five North American T-6G Texan training aircraft.[94] This aircraft returned to the U.S. and, after briefly being registered as N9307R and N19903, is now restored and at the Smithsonian Museum as NC19903.[95][96]
Aigle Azur and Union Aéromaritime de Transport
Aigle Azur Extrême-Orient Boeing S-307 Strato-Clipper F-BHHR in New York just before deliveryAigle Azur Boeing SA-307B-1 F-BELV on the ramp
TWA sold all five TWA SA-307B-1s to the French operator Aigle Azur (French for Blue Eagle) in April 1951, for $525,000,[notes 26] along with their remaining supply of spares.[63]Aigle Azur received them between May 14, 1951, and December 19, 1951.[56] The modified the craft in Bordeaux for 48-passenger capacity and used them on scheduled flights between Paris and North and Central Africa (Casablanca, Dakar, Tunis), Madagascar, French West Africa, and French Equatorial Africa, and later in 1952, French Indo-China.[46][63][97]
The Stratoliners were no longer competitive against the larger and faster Douglas DC-6 and Lockheed Constellation then entering service,[46] which on May 1, 1955, led to Aigle Azur along with its subsidiary in Asia, Aigle Azur Indochine, being bought by Union Aéromaritime de Transport (UAT). On the same date, Aigle Azur Indochine was renamed Aigle Azur Extreme-Orient. On September 16, 1955, F-BELV, F-BELX, F-BELY, and F-BELZ were transferred from Europe to Aigle Azur Extreme-Orient, mainly for charter work.[98] During 1955 and 1956, F-BELU and F-BELY and F-BELZ returned to Europe to be leased to Airnautic.[99] The former Pan Am aircraft, F-BHHR, had joined Aigle Azur in 1951 and was transferred to Aigle Azur Extreme-Orient in March 1957.[93]Aigle Azur Extrême-Orient branding was retained for several years before the aircraft were repainted in UAT Aéromaritime colors.
After four years in service in Asia, during which it was briefly leased to Air Laos Transport Aériens (later renamed Royal Air Lao) and assigned the Laotian XW registration XW-TAC, F-BHHR was destroyed in an accident on May 22, 1961, while being operated by Aigle Azur Extreme-Orient on a non-scheduled Saigon–Vientiane passenger flight, with 28 on board. It had departed from Tan Son Nhat International Airport in Saigon and was heading for Vientiane when the number four engine had to be shut down, and when it returned to land it overshot the runway in deteriorating weather and a violent squall or microburst blew it sideways, causing it to hit the ground. All 28 people on board survived but the aircraft was destroyed.[100]
Airnautic (or Air Nautic) received three ex-Aigle Azur SA-307B-1s in 1955 and 1956 including F-BELU,[101]F-BELY,[102] and F-BELZ,[103] which were operated in southern Europe around the Mediterranean providing charter flights, especially around Corsica.
On December 29, 1962, F-BELZ collided with a mountain while on a charter flight with 22 basketball players and fans while flying from Bastia to Ajaccio, on the island of Corsica.[97][103][104] It was flying at an altitude of about 7,500ft (2,300m), despite having been cleared for 12,000ft (3,700m), and at 12:12pm slammed into a sheer rock face just 165ft (50m) from the peak, before falling about 330ft (100m) down the side of the mountain.[104]
In 1965, F-BELY and F-BELU were returned to CITCA, who then leased them to other operators.[101][102]
Air France became the principal shareholder of Airnautic in 1962, at which time it purchased DC-6s,[105] and in 1966 Airnautic ceased to exist, having been absorbed into Air France.
Compagnie Internationale de Transports Civil Aériens (CITCA)
Boeing SA-307B-1 Stratoliner F-BELX, likely while with Cambodia Air CommercialSA-307B-1 F-BELU with the CIC/ICCRoyal Air Lao SA-307B-1 XW-TFP two days before ditching in the Mekong river
In 1965, Cambodia Air Commercial leased F-BELY as XW-PGR, and F-BELU as XW-TFP, before both went to Royal Air Lao the same year,[101][102] which then leased all five of the CITCA Stratoliners, which were also assigned Laotian XW registrations, and F-BELV became XW-TAA and F-BELXXW-TFR.[98][99] The Air Laos Transport Aériens and Royal Air Lao Stratoliners were flown between Vientiane and Hong Kong with a large detour around North Vietnam.[97] Royal Air Laos was operating XW-TFP and XW-PGR when they were destroyed in accidents,[101][102] while F-BELV would be leased to Royal Air Cambodge.[98]
On February 27, 1971, XW-PGR collided with a Lao Air Force Douglas C-47 while landing at Luang Prabang, Laos, and damage to the left wing was irreparable due to a lack of spares.[64][106]
The International Control Commission (ICC; French: Commission Internationale de Contrôle, or CIC) and its successor, International Commission of Control and Supervision, leased three aircraft in 1964 under their old French registrations of F-BELV, F-BELU, and F-BELX, which then had seating for as many as 60 and were used to provide what were often hazardous diplomatic flights around South-East Asia until 1974, when it suspended operations with the impending defeat of US forces in Vietnam.[46][98][99] They were flown under diplomatic immunity along specially delineated 20mi (32km) wide corridors between Saigon in South Vietnam, Vientiane in Laos, Phnom Penh in Cambodia, and Hanoi in North Vietnam.[97] Passengers were usually diplomats, members of the Red Cross, press, businessmen, and Control Commission officials.[97]
When F-BELV disappeared on October 18, 1965, it was flying from Vientiane-Wattay Airport in Laos to the Gia Lam Airport (Hanoi), in Vietnam,[64][107] and was supposed to have been cleared to fly at 11,800ft (3,600m) and 165kn (190mph; 306km/h).[108] On this flight there were five CIC delegates from India, three from Canada, and one from Poland, as well as four French crew members,[108] and all passengers and crew died.[107] Due to radio interference a message indicating that their clearance period had been delayed was never received.[108] Poor communications meant it took around 19 hours before anyone realized the aircraft had gone missing as the destination airport had assumed it had returned to its point of origin, and that airport was unaware it had not arrived at its destination.[108] The search for the downed aircraft was delayed further due to the need to negotiate access to the likely crash area, with several warring parties wary from previous experience of the search mission being a cover for intelligence gathering or other military activities.[108] A Canadian investigation long after the war determined that the craft had likely been shot down by North Vietnamese anti-aircraft fire, but they were unable to determine if it was intentional or not.[107]
XW-TFR (previously F-BELX and briefly XW-TAB) had been returned to Cambodia Air Commercial when it was destroyed in an accident on June 27, 1974, following three of the four engines failing while climbing out from Battambang Airport. During the forced landing it collided with trees, causing extensive damage including one wing being torn off before the aircraft caught fire. Seventeen passengers and two crew members out of the 39 on board died in the crash that the crash investigation blamed on poor maintenance.[46][97][109]
The pilot of XW-TFP was forced to ditch in the Mekong river on March 13, 1975, near the Laos–Thailand border while on a flight from Hong Kong to Vientiane. Both the pilot and co-pilot escaped the wreck but were captured by the communist Pathet Lao and held until May. The wreckage was still there in 1986.[110]
Operators
Pan Am Boeing S-307 Strato-Clipper NC19910 Clipper Comet
Civilian operators
TWA Stratoliner pre-war, at Chicago airportQuaker City Airways Boeing S-307 Stratoliner N75385
United States Army Air Forces operated five ex-TWA SA-307Bs as C-75s. Three Pan Am 307s operated under USAAF direction, but ownership remained with Pan Am.
Accidents and incidents
The Boeing 307 was involved in eight hull-loss incidents with 67 fatalities. Four of the ten incidents involved fatalities, with one craft likely being shot down while in a war zone.[114]
Test flight before ferry to new operator with known fuel leaks of unknown origin. In-flight muffled cabin explosion followed by fire. Safely landed on rock-strewn mesa, but fire consumed aircraft.
The sole intact Boeing 307 Stratoliner, NC19903, is preserved in flying condition at the Smithsonian's Steven F. Udvar-Hazy Center. After having been restored to flying condition, it was being delivered to the Smithsonian on what was to be its last flight when it ran out of fuel and ditched in Elliott Bay in Seattle, Washington, on March 28, 2002.[120] Despite the incident, it was raised and again restored, and it completed its flight to the Smithsonian, where it was placed on display.[121]
The forward fuselage of Howard Hughes' 307 (NX19904) also survives, although it was stripped of flying surfaces and the rear fuselage and converted into a houseboat. The aircraft was awaiting restoration at Fort Lauderdale International Airport in August 1964 but was severely damaged when Hurricane Cleo tore it loose from its tiedowns and it was blown into a stand of trees. The aircraft was later salvaged and converted into a houseboat, and the interior remains notable for the additions made when owned by Hughes.[122][123] It was part of the Florida Air Museum collection.[124] As per a Kermit Weeks Facebook post, in February 2024, it was stored with Weeks' collection at the Fantasy of Flight Museum in Florida.[125]
Specifications (Boeing SA-307B, ATC#726)
Boeing SA-307B Stratoliner three-view drawing
Data fromJuptner, Joseph P. (1980). US Civil Aircraft: Vol. 8 (ATC 701–800). Aero Publishers. pp.102–104. ISBN978-0816891788.[126]
General characteristics
Crew: Five, including pilot, co-pilot, flight engineer and two flight attendants
Capacity: Daytime seating for 33, nighttime capacity 25, in 16 berths and 9 reclining chairs
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