Boeing 377 Stratocruiser

The Boeing 377 Stratocruiser was a civil derivative of the Boeing Model 367, the Boeing C-97 Stratofreighter, which first flew in late 1944. William Allen, who had become president of the Boeing Company in September 1945, sought to introduce a new civilian aircraft to replace reduced military production after World War II. Boeing saw in their large-bodied, fast, and long-ranged military transport potential for a passenger aircraft suited for premium service on long transoceanic routes, expanding on the precedent set by their Boeing 314 Clipper with Pan American World Airways. Despite a recession in late 1945, Allen ordered 50 Stratocruisers, spending capital on the project without an order from an airline customer. On November 29, 1945, Pan American World Airways (Pan Am) became the launch customer with the largest commercial aircraft order in history, a $24.5 million order for 20 Stratocruisers. The 377 shared the distinctive design of the C-97, with a "double-bubble" fuselage cross-section, resembling a figure-8, with the smaller loop on the bottom, and of interior space shared between two passenger decks. Outside diameter of the upper lobe was 132 inches, compared to 125 inches for the DC-6 and other Douglas types (and 148 inches for today's 737). The lower deck served as a lounge, seating 14. The 377 had innovations such as higher cabin pressure and air conditioning; the superchargers on the four Pratt & Whitney R-4360 engines increased power at altitude and allowed constant cabin pressure. The wing was the Boeing 117 airfoil. In all, 4 million man-hours went into the engineering of the 377. It was one of only a few double-deck aircraft ever built for commercial use, another being its French contemporary, the Breguet Deux-Ponts, as well as later models, the 747 and the Airbus A380. The first flight of the 377 was on July 8, 1947, two years after the first commercial order. The flight test fleet of three 377s underwent of flying to test its limits before certification. Other carriers who adopted the Stratocruiser were British Overseas Airways Corporation, American Overseas Airlines (merged with Pan Am in 1950) and United Airlines. The last 377 was delivered to BOAC in May 1950. On this delivery flight, Boeing engineer Wellwood Beall accompanied the final 377 to England, and returned with news of the de Havilland Comet, the first jet airliner, and its appeal. ==Operational history==

377 over the Golden Gate Bridge Stratocruiser As the launch customer, Pan Am was the first to begin scheduled flights, from San Francisco to Honolulu in April 1949. At the end of 1949, Pan Am, BOAC and American Overseas Airlines (AOA) were flying 377s transatlantic, while Northwest Orient Airlines was flying in the United States; in January 1950, United began flights from San Francisco to Honolulu. Stratocruisers were pressed into emergency military service after the onset of the Korean War. By late 1952, Northwest Stratocruisers replaced DC-4s to Tokyo via Anchorage, Alaska; Northwest replaced the Stratocruiser on the Honolulu run in 1953 and to Tokyo in 1955. For a short time, Pan Am 377s flew to Beirut, Lebanon, but after 1954, no 377 was scheduled east of Europe or west of Singapore. In 1954, United Stratocruisers flew Los Angeles to Honolulu and between Seattle and San Francisco; United's B377 flights to Honolulu were all first class. In 1955, BOAC 377s had 50 First Class seats (fare $400 one way New York to London) or 81 Tourist seats (fare $290). In 1956, Pan Am 377s flew from Los Angeles and San Francisco to Sydney with stops at Honolulu, Canton Island and Suva (via Nadi Airport in Fiji). By 1958, Pan Am was operating the Stratocruiser between Seattle, Washington and Fairbanks, Juneau and Ketchikan, Alaska and between Seattle and Whitehorse, Yukon. Within six years of first delivery, the Stratocruiser had carried 3,199,219 passengers; it had completed 3,597 transcontinental flights, and 27,678 transatlantic crossings, and went between the United States and South America 822 times. In these first six years, the Stratocruiser fleet had flown 169,859,579 miles (273,362,494 km). The propellers were the subject of Airworthiness Directives in 1955, 1957, and 1958. In 1950, United's seven 377s averaged $2.46 "direct operating cost" per plane-mile, and "Indirect costs are generally considered to be equal or greater than the direct costs." Most operators used Stratocruisers on long-range routes where higher prices could be charged, off-setting the higher operating costs. The exception was Northwest Airlines, which managed to keep the aircraft competitive on shorter U.S. domestic routes where the aircraft's higher payload capacity benefited from lower fuel weights. United however could not integrate their six-plane fleet of 377s. By 1954, the lack of spares and the inability to cross-train their Douglas crews with the type relegated their Stratocruisers primarily to their Hawaii route, where they faced stiff competition from Pan American and Northwest. By the end of that year, the six United 377s were all sold to BOAC in a deal orchestrated by Douglas Aircraft. BOAC, which was short of aircraft following the grounding of the Comet 1, paid between US$895,000 and US$995,000 per unit and spares for what were essentially five-year-old aircraft. In 1954, an equivalent brand new Douglas DC-7 cost US$775,000 (~$ in ). Boeing set the never-exceed speed at IAS but in testing, the 377 reached IAS (about TAS) in a 15–20 degree dive at ; another report said it reached true airspeed while diving from altitude to in 50 seconds using "full rated power". Typical airline cruise was less than ; in August 1953, Pan Am and United 377s (and United DC-6s) were scheduled between Honolulu and San Francisco () in 9 h 45 min each way. The longest (by distance) 377 nonstop flights were made by Pan Am from Tokyo to Honolulu during four winter seasons beginning in 1952–1953. In January 1953, two nonstops a week were scheduled with a flight time of 11 hr 1 min due to tailwinds; the following August all flights took 19 hours, with a stop at Wake Island Airfield. In winter 1953-54, one Tokyo-Honolulu flight took 9 hr 35 min for . By 1960, Stratocruisers were being superseded by jets: the de Havilland Comet, Boeing 707, and Douglas DC-8. The last flight of the 377 with United was in 1954, the last with BOAC was in 1959, and the last with Northwest was in September 1960. In November 1960, only a weekly Pan Am Honolulu to Singapore flight remained, and the 377 was retired by Pan Am in 1961. High operating costs (notably the fuel consumption and maintenance of the Wasp Major engines) led to rapid abandonment of the 377 with the onset of the jet era. Boeing 377 During 1959 and 1960, Transocean Air Lines (TAL) assembled a fleet of fourteen at bargain prices. In 1960, TAL went bankrupt and only four were in operable condition. The hulks were stored at Oakland International Airport through the 1960s and cannibalized for parts, contributing some to the Aero Spacelines Guppies. Five remaining 377s were modified by Bedek Aviation to resemble former U.S. Air Force Model 367 Stratofreighters and pressed into service with the Israel Defense Forces. Two were shot down during the course of their service and the three remaining 377Ms were retired in 1978 and later scrapped. None of the 56 377s built were preserved for display in original condition, although one airframe remains today as the Mini Guppy; the IAF Museum in Israel has a C-97 (4X-FPM) on display painted to resemble their most famous 377M, Masada. ==Variants==

;377-1 :Proposed variant to be powered by Wright R-3350 Duplex-Cyclone engines. It was to be fitted with the flaps and deicing boots from the B-29. ;377-6 :Proposed variant to be powered by supercharged Allison V-3420 engines. 20 new aircraft built, plus one converted from the 377-10-19 prototype. ;377-10-26S Super Stratocruiser :10 refitted with more powerful engines and a larger fuel capacity for Pan American transatlantic flights. ;377-10-29 :Eight delivered to American Overseas Airlines with round windows for the main cabin and rectangular windows for the lower cabin. ;377-10-30 :Ten for Northwest Orient Airlines with all rectangular windows. ;377-10-34 :Seven for United Air Lines. Rectangular windows on the main cabin and circular windows on the lower cabin. ;377-11 :Proposed variant to be powered by Wright XA-395 turbine engines. ;377-28-26 :Proposed six-engined variant for Pan American World Airways. It was to be powered by two Wright R-1820 Cyclone engines mounted outboard of the four standard R-4360s, and it would have carried two external fuel tanks from the B-50. Seating would have been identical to that of the 377-10-26. Four were built and were used by Airbus to carry aircraft parts between its factories. In the 1990s, Airbus retired them due to rising operational costs and they have been replaced with Airbus Belugas. Two of the former Airbus Industrie Super Guppies remain in Germany and France, with a third being scrapped in December 2020 after eleven years of restoration at Bruntingthorpe Aerodrome in the UK. The fourth aircraft was acquired by NASA as part of a barter agreement with ESA for its role as a partner with the International Space Station. ;Aero Spacelines 377MG Mini Guppy :Conversion of a 377-10-26, it featured a larger main cabin for oversize cargo, stretched wing and a hinged tail. ;Aero Spacelines 101 Mini Guppy Turbine :Originally designated the 377MGT. Similar to the 377MG, but powered by Pratt & Whitney T34-PWA turboprop engines. Two built. ==Operators==

in front of a 377 '''''' • Línea Internacional Aérea • Ghana Airways (Leased from BOAC) '''''' • British Overseas Airways Corporation (BOAC) '''''' • Israeli Air Force '''''' • Nigeria Airways (Leased from BOAC) '''''' • Svensk Interkontinental Lufttrafik, part of Scandinavian Airlines System (aircraft not delivered - passed to BOAC) '''''' • American Overseas Airlines • Northwest Orient Airlines • Pan American World Airways • Transocean Air Lines • United Airlines '''''' • Rutas Aéreas Nacionales SA ==Accidents and incidents==

This aircraft type suffered 13 hull-loss accidents between 1951 and 1970 with a total of 139 fatalities. The worst single accident occurred on April 29, 1952. The aircraft type also experienced a significantly high rate of in-flight emergencies related to engine and propeller failure, resulting in Airworthiness Directives. Faults included structural failures of neoprene-cored propellers, failures of propeller pitch control resulting in overspeed, and failures related to engine cooling. Six propeller failures between 1950 and 1955 resulted in separation or near-separation of engines from mounts, with two resulting in hull-loss accidents. Directives were issued in 1950, 1955, and 1958 regarding enhanced maintenance and fault detection, in-flight vibration monitoring, and propeller replacement. ; September 12, 1951 : United Air Lines Flight 7030, a Stratocruiser 10-34 (N31230, named Mainliner Oahu), was being used for a semi-annual instrument check of a captain. At 11:39 PDT, the flight was cleared for an ILS approach to the San Francisco Airport. The aircraft, with No. 4 propeller feathered, stalled and abruptly dived from an altitude of approximately 300 feet and was destroyed upon impact in San Francisco Bay. All three crew aboard were killed. The probable cause was an inadvertent stall at low altitude. ; April 29, 1952 : Pan Am Flight 202, a Stratocruiser 10-26 (N1039V, named Clipper Boa Esperança aka Clipper Good Hope) en route from Buenos Aires-Ezeiza and Rio de Janeiro–Galeão to New York via Port of Spain crashed in the jungle in the south of the State of Pará. Probable causes are the separation of the second engine and propeller from the aircraft due to highly unbalanced forces followed by uncontrollability and disintegration of the aircraft. All 50 passengers and crew died in the worst-ever accident involving the Boeing 377. ; July 27, 1952 : Pan Am Flight 201, a Stratocruiser 10-26 (N1030V) en route from New York and Rio de Janeiro-Galeão to Buenos Aires-Ezeiza suffered explosive decompression at about 12,000 feet about 20 miles south of Rio de Janeiro. A passenger was blown out and the cabin considerably damaged, but the aircraft was able to return to Rio de Janeiro and make a safe landing. The main cabin door had not been properly locked. ; December 25, 1954 : A BOAC Stratocruiser 10-28 (G-ALSA, named RMA Cathay) crashed on landing at Prestwick at 0330 hours, killing 28 of the 36 passengers and crew on board. The aircraft had been en route from London to New York City, when, on approach to Prestwick, it entered a steep descent before leveling-out too late and too severely, hitting the ground short of the runway. ; March 26, 1955 : Pan Am Flight 845/26, a Stratocruiser 10-26 (N1032V, named Clipper United States), ditched 35 miles (56 km) off the Oregon coast after the no. 3 engine and propeller tore loose from the wing, causing severe control difficulties. The aircraft sank after 20 minutes in water of about 1,600 m (5,200 ft) depth. There were four fatalities out of the 23 occupants, including two of the crew. ; April 2, 1956 : Northwest Orient Airlines Flight 2, a Stratocruiser 10-30 (N74608, named Stratocruiser Tokyo), ditched into Puget Sound after the flight engineer mistakenly failed to close the cowl flaps on the plane's engines, an error attributed to confusing instrument layout. Although all aboard escaped the aircraft after a textbook ditching, four passengers and one flight attendant succumbed either to drowning or to hypothermia before being rescued. ; October 16, 1956 : ditches near Hawaii Pan Am Flight 6, a Stratocruiser 10-29 (N90943, named Clipper Sovereign of the Skies), ditched northeast of Hawaii during the last leg of an around-the-world flight from Philadelphia to San Francisco after two of its four engines failed following an overspeed incident. ; April 10, 1959 : At the conclusion of a flight from Seattle to Juneau, Alaska, a Pan Am Stratocruiser 10-26 (N1033V, named Clipper Midnight Sun) undershot on final approach and collided with an embankment. The aircraft caught fire and was destroyed, but all 10 passengers and crew survived. ; July 9, 1959 : A Pan Am Boeing Stratocruiser 10-29 (N90941, named Clipper Australia) belly landed at Haneda Airport following landing gear problems; all 59 passengers and crew on board survived, but the aircraft was written off. ; August 1967 : An Aero Spacelines Stratocruiser 10-29 (N90942) suffered a ground collision with Stratocruiser 10-32 N402Q at Mojave, California; the aircraft was damaged beyond repair. ; May 12, 1970 : An Aero Spacelines 377MGT (N111AS) was being test flown following conversion from a Boeing 377. During the sixth takeoff with one engine shut down, the aircraft turned and rolled to the left. The left wingtip then struck the ground and the aircraft yawed severely after which the forward fuselage struck the ground, destroying the cockpit. All four crew died. ==Specifications (377)==