Boeing 377 Stratocruiser

The Boeing 377 Stratocruiser was a large long-range airliner developed from the C-97 Stratofreighter military transport, a derivative of the B-29 Superfortress. The Stratocruiser's first flight was on July 8, 1947. Its design was advanced for its day, its innovative features included two passenger decks and a pressurized cabin, a relatively new feature on transport aircraft. It could carry up to 100 passengers on the main deck plus 14 in the lower deck lounge; typical seating was for 63 or 84 passengers or 28 berthed and five seated passengers.

The Stratocruiser was larger than the Douglas DC-6 and Lockheed Constellation and cost more to buy and operate. Its reliability was poor, chiefly due to problems with the four 28-cylinder Pratt & Whitney Wasp Major radial engines and their four-blade propellers. Only 55 Model 377s were built for airlines, along with the single prototype.

Design and development
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 Second World War. Although in a recession in late 1945, Allen ordered 50 Stratocruisers, spending capital on the project without an airline customer.

On November 29, 1945 Pan American World Airways became the launch customer with the largest commercial aircraft order in history, a $24.5 Million order for 20 Stratocruisers, about $324.3 Million in 2014 dollars. Earlier in 1945 the Boeing C-97 had flown from Seattle to Washington, D.C. nonstop in six hours and four minutes; with this knowledge, and with Pan Am President Juan Trippe's high regard for Boeing after their success with the Boeing 314 Clipper, Pan Am was confident in ordering the expensive plane.

The 377 shared the distinctive design of the C-97, with a "double-bubble" fuselage cross-section, resembling a figure-8, with 6,600 ft³ (187 m³) of interior space, allowing for pressurization of a large cabin with 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 consistent cabin pressure. The wing was the Boeing 117 airfoil, regarded as the "fastest wing of its time". In all, 4,000,000 man-hours went into the engineering of the 377.

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 250,000 smi of flying to test its limits before certification.

Operational history
As the launch customer, Pan Am was the first to begin scheduled service, from San Francisco to Honolulu in April 1949. At the end of 1949 Pan Am, BOAC, and AOA were flying 377s transatlantic, while Northwest was flying in the United States; in January 1950 United began flights from San Francisco to Honolulu. For a short time Pan Am flew their 377s to Beirut, but after 1954 no 377 was scheduled east of Europe or west of Singapore. In 1955 BOAC B377s had 50 First Class seats (fare $400 one way New York to London) or 81 Tourist seats (fare $290).

Despite a service record plagued by one or two early disasters arising from the Curtiss Electric propellers fitted to early production aircraft, the 377 was one of the most advanced, and capable of the propeller-driven transports, and among the most luxurious. A total of 56 were built, one prototype (later reconditioned) and 55 production aircraft. 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). It was also one of but a few double deck airliners, another being its French contemporary the Breguet Deux-Ponts, as well as Boeing's own 747 and the Airbus A380. 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.

The last flight of the 377 with United was in 1954, the last with BOAC was in 1959, and the last Northwest was in September 1960. By November 1960 only a weekly Pan Am Honolulu to Singapore flight remained, and the 377 was retired by Pan Am in 1961.

In 1953, "United's Ray Ireland ... described the Stratocruiser as unbeatable in luxury attraction but is uneconomical. Ireland said PAA's Stratocruiser competition to Hawaii induced United to buy the plane originally." In 1950 United's seven B377s averaged $2.46 "direct operating cost" per plane-mile, and "Indirect costs are generally considered to be equal or greater than the direct costs." So a 57-passenger B377 was unlikely to make money, in 1950 anyway. At the end of 1954 the six United B377s were sold to BOAC, which was short of aircraft after the grounding of the Comet 1.

Boeing set never-exceed speed at 351 miles per hour (565 km/h) IAS or Mach 0.62, but on test the B377 reached 409 miles per hour (658 km/h) IAS in a 15–20 degree dive at 13,500 feet (4,100 m), Mach 0.67 and about 500 mph TAS. Typical airline cruise was less than 300 miles per hour (480 km/h); in August 1953 Pan Am and United B377s (and United DC-6s) were scheduled between Honolulu and San Francisco (2,398 miles (3,859 km)) in 9 h 45 min each way.

The longest (by distance) B377 nonstops were Pan Am Tokyo to Honolulu in four winters starting in 1952–1953. In January 1953 two nonstops a week were scheduled 11 hr 1 min on the strong tailwinds; the following August all flights took 19 hours via Wake.

By 1960 Stratocruisers were being superseded by jets such as the de Havilland Comet, Boeing 707, and Douglas DC-8. A few were sold to smaller airlines, used as freighters; or converted by Aero Spacelines into outlandishly enlarged freighters called Guppies. As the airlines began to upgrade so did the military services. The Boeing 377 was mainly used by two militaries, the United States and Israel.

Variants

 * 377-10-19
 * Prototype Stratocruiser; one built. Later brought up to 377-10-26 standard and sold to Pan American World Airways in 1950.


 * 377-10-26
 * 20 delivered to Pan American World Airways with round windows and a rear galley.


 * 377-10-26S
 * 10 refitted with more powerful engines and a larger fuel capacity for Pan American transatlantic flights. Called the "Super Stratocruiser".


 * 377-10-28
 * Four ordered by the Scandinavian Airlines System, but taken up by BOAC after SAS cancelled the order. Aircraft had similar features to the 377-10-26.


 * 377-10-29
 * Eight delivered to American Overseas Airlines with round windows for the main cabin and rectangular windows for the lower cabin as well as an aft galley. AOA was merged with Pan Am the year after their delivery.


 * 377-10-30
 * Ten for Northwest Orient Airlines with all rectangular windows and an aft galley.


 * 377-10-32
 * Six for the British Overseas Airways Corporation (BOAC). Had a midships galley and all cabin windows were circular.


 * 377-10-34
 * Seven for United Air Lines. Rectangular windows on the main cabin and circular windows on the lower cabin. Sold to BOAC circa 1954.


 * 377F
 * Freighter conversion.


 * 377M
 * In the early 1960s the Israeli Air Force wanted to upgrade to the C-130 Hercules, which could lift larger payloads, but it was expensive and sales were embargoed by the United States. Israeli Aircraft Industries at Ben Gurion International Airport offered to modify Boeing 377 Stratocruisers. It had a stronger cabin floor which could handle cargo, plus a C-97 military Statocruiser tail section, which included a clamshell cargo door. These were dubbed Anak (or Giant in Hebrew) and entered service in 1964. Three of these were modified by the use of a swing tail section, similar to the Canadair CL44D-4 airliner. Two others served as aerial tankers with underwing hose reel refuelling pods. Two others were ELINT-platforms for electronic reconnaissance, surveillance and ECM (Electronic Counter Measures) missions. These were later joined by four KC-97G's with the flying boom system.

Aero Spacelines Guppy
In addition to the Israeli Anaks a company called Aero Spacelines was converting old 377s to aircraft called Guppys in the 1960s. There were three types: the Pregnant Guppy, Super Guppy, and Mini Guppy. They had an extension to the top of the fuselage to enable them to carry large aircraft parts between manufacturing sites.

The first was the Pregnant Guppy, followed by the Super Guppy, and finally the Mini Guppy. The Super Guppy and the Mini Guppy had turboprop engines.


 * Aero Spacelines 377PG Pregnant Guppy
 * Conversion of one 377-10-26, incorporating an enlarged upper deck and a fuselage lengthened by 16 feet to carry sections of the Saturn V rocket. One converted.


 * Aero Spacelines 377SG Super Guppy
 * A single heavy-lift transport similar to the Pregnant Guppy built by Aero Spacelines. The aircraft contained parts of a YC-97J Stratofreighter and a 377-10-26 mated with a larger main fuselage, larger tail and Pratt & Whitney T34 turboprops.


 * Aero Spacelines SGT-201 Super Guppy Turbine
 * Originally designated the 377SGT, it was similar to the 377SG, but with a more aerodynamic fuselage, a Boeing 707 nosewheel, wingspan stretched by 23 feet, and four Allison 501-D22C turboprops. 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. Three of the former Airbus Industrie Super Guppys remain in the U.K., Germany, and France, while 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 MGT-101 Mini Guppy Turbine
 * Originally designated the 377MGT. Similar to the 377MG but powered by Allison 501-D22C turboprop engines. One built.

Operators

 * Línea Internacional Aérea
 * Israeli Air Force
 * Svensk Interkontinental Lufttrafik part of Scandinavian Airlines System (aircraft not delivered - passed to BOAC)
 * British Overseas Airways Corporation
 * American Overseas Airlines
 * DAI Airways
 * Northwest Orient Airlines
 * Pan American World Airways
 * Transocean Air Lines
 * United Airlines
 * Rutas Aéreas Nacionales SA
 * Northwest Orient Airlines
 * Pan American World Airways
 * Transocean Air Lines
 * United Airlines
 * Rutas Aéreas Nacionales SA
 * Rutas Aéreas Nacionales SA

Accidents
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.


 * 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 10:39, 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 demolished 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 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 following pressurization problems during climb from Rio de Janeiro, a door blew open, a passenger was blown out and the cabin considerably damaged. One passenger (of 27 on board) died.
 * 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 levelling-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) deep. 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: Pan Am Flight 6, a Stratocruiser 10-29 (N90943, named Clipper Sovereign of the Skies), ditched northeast of Hawaii after two of its four engines failed. The aircraft was able to circle around USCGC Pontchartrain until daybreak, when it ditched; all 31 on board survived.
 * November 8, 1957: Pan Am Flight 7, a Stratocruiser 10-29 (registered N90944, named Clipper Romance of the Skies), left San Francisco for Hawaii with 38 passengers and 6 crew. The 377 crashed around 5:25 p.m. in the Pacific Ocean. There were no survivors and the entire wreckage has never been found. Only 19 bodies and bits of debris were recovered. There is speculation that two passengers had a motive to bring the plane down. Eugene Crosthwaite, a 46-year-old purser, had shown blasting powder to a relative days prior to the flight, and had cut a stepdaughter from his will only one hour before the flight. William Payne, an ex-Navy demolitions expert, had taken out large insurance policies on himself just before the flight, and had a $10,000 debt he was desperate to pay off. The insurance investigator later suspected him of never being on the plane. His wife received at least $125,000 in payouts.
 * June 2, 1958: A Pan Am Stratocruiser 10-26 (registration N1023V, named Clipper Golden Gate) was on a flight from San Francisco to Singapore with some in-between stops. As the aircraft touched down at Manila (runway 06) in a heavy landing in rainy and gusty conditions, the undercarriage collapsed (as a result of the hard landing). The plane skidded and swerved to the right, coming to rest 2850 feet past the runway threshold and 27 feet from the edge of the runway. One of the passengers was killed when one of the blades of the number 3 prop broke off, penetrating the passenger cabin.
 * 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 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) was on final for Haneda Airport when the gear was extended, showing three greens. When power was reduced prior to touchdown, the gear unsafe warning horn sounded and a red gear unsafe warning light illuminated. The captain first called for a go-around, but noticed that the airspeed was too low. The gear was retracted quickly and a belly landing was carried out. 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: The Aero Spacelines 377MGT was a converted Boeing Stratocruiser. Prototype N111AS first flew on March 13, 1970. In the following period flight testing was carried out, a.o. at Edwards AFB. The accident occurred during the sixth takeoff of Flight Number 12 following the scheduled shutdown of the engine number one at about 109 knots IAS (indicated air speed). The takeoff was being made on runway 22 and the wind was from approximately 200 degrees at about 10 knots. Rotation occurred at about 114 knots and several seconds after rotation, according to one witness, the aircraft turned and rolled to the left, settling as it did so. The left wingtip subsequently contacted the ground, causing a severe yaw. The forward fuselage struck the ground, causing the flight deck to be destroyed. All four crew aboard were killed.