Boeing 377 Stratocruiser
Pan Am Stratocruiser Clipper Seven Seas arriving at London Heathrow in September 1954.
Role	Airliner
Manufacturer	Boeing
First flight	July 8, 1947
Retired	1963
Status	Retired
Primary users	Pan Am BOAC Northwest
Number built	56
Developed from	C-97 Stratofreighter
Variants	Pregnant Guppy Super Guppy Mini Guppy

The Boeing 377, also called the Stratocruiser, was a large long-range airliner built after World War II. It was developed from the C-97 Stratofreighter, a military derivative of the B-29 Superfortress used for troop transport. The Stratocruiser's first flight was on July 8, 1947.^[1]

Released in the late 1940s, the aircraft was powered by four piston engines, driving tractor propellers. The aircraft was able to cruise at about 32,000 feet. It also had a pressurized cabin, which was a relatively new feature to transport aircraft at the time, and two decks. Airlines were able to make transoceanic flights easier and faster with the new aircraft, which enabled easier international travel to places such as Hawaii.^[1]

Nevertheless, the Stratocruisers did not have great reliability (chiefly due to chronic problems with the extremely complex^{[citation needed]} 28-cylinder R-4360 engines and the associated propellers) and only 56 were built for airlines.

Design and development[link]

Like the C-97, the 377 was developed towards the end of World War II by adapting an enlarged upper fuselage onto the lower fuselage and wings, which were essentially the same as those of the B-50 Superfortress, the high-performance evolution of the B-29 Superfortress bomber. The 377 was larger and longer-ranged than the Lockheed Constellation and Douglas DC-6, with nonstop transatlantic range eastbound. Production ended in 1950.^[2]

The "inverted-figure-8" double-deck fuselage design provided 6,600 ft³ (187 m³) of interior space where the lower deck had a smaller diameter than the upper deck. It offered seating for over 100 passengers, or sleeping berths for up to 28 berthed and five seated passengers. It first flew on July 8, 1947. It had the speed and range to span ocean routes, enabling flying from New York to Hawaii in less than 24 hours.^[3] Pressurization (previously introduced on the Boeing Stratoliner and also designed into the B-29) allowed sea-level cabin pressure at 15,500 ft (4,700 m) altitude. At 25,000 ft (7,600 m), passengers enjoyed a "cabin altitude" of only 5,500 ft (1,700 m).

Operational history[link]

Despite a service record^[4] remembered for one or two early disasters arising from a propeller design fitted to the Stratocruiser in its earlier years, Boeing's remarkable airliner was one of the most capable of post-war propeller-driven transports, and certainly among the most luxurious. Only 55 were built as airliners, joined eventually by the reconditioned prototype to make a total of 56. Another 60 of this general design, with significant engineering differences, were built as C-97 military transports, but the majority were built as KC-97 tankers.

The Stratocruiser flew premier services to Hawaii, across both oceans, and elsewhere in the world. It was one of the few airliners with a double-decker seating arrangement (another was the French Breguet Deux-Ponts) until the 747, though some airlines did have lower-level lounges on their L-1011 Tristar aircraft. The upper deck was for 55-100 passenger seats or 28 sleeper berths, while the lower deck had a lounge and bar. Passengers could walk down and get a drink on the long flights, once the plane levelled off at cruising altitude.^{[citation needed]}

In the early 1960s these planes were starting to become superseded by jets such as the de Havilland Comet, Boeing 707 and Douglas DC-8. A few survived to be sold to smaller airlines, used as freighters or converted into a specialised freighter called a Guppy. As the airlines began to upgrade so did the militaries that were using them. The Boeing 377 was primarily used in only two militaries, the US and Israeli, both of which began buying jet engine aircraft and replacing their 377s.^{[citation needed]}

Operators[link]

American Overseas Airways Stratocruiser.

BOAC Stratocruiser G-AKGJ "RMA Cambria" at Manchester operating a New York flight in 1954

 Ecuador

• Línea Internacional Aérea

 Israel

• Israeli Air Force

 United Kingdom

• British Overseas Airways Corporation

 United States

• American Overseas Airlines
• Northwest Orient Airlines
• Pan American World Airways
• Transocean Air Lines
• United Airlines

 Venezuela

• Rutas Aéreas Nacionales SA

 Denmark  Sweden  Norway

• Scandinavian Airlines System (aircraft not delivered - passed to BOAC)

Safety record[link]

This aircraft type suffered 13 hull-loss accidents between 1951 and 1970 with a total of 140 fatalities. The worst single accident occurred on April 29, 1952.

• 12 Sept 1951: United Air Lines' Boeing Stratocruiser "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. probable cause was an inadvertent stall at low altitude.
• 29 April 1952: Pan Am Boeing 377 Stratocruiser 10-26 registration N1039V operating flight 202 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 no. 2 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.^[5]
• 27 July 1952: Pan Am Boeing 377 Stratocruiser 10-26 registration N1030V operating flight 201 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 died.^[6]
• 25 December 1954: British Overseas Airways Corporation Stratocruiser 10-28 G-ALSA crashed on landing at Prestwick at 0330 hours, killing 28 of the 36 passengers and crew onboard. 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. A number of factors have been attributed to the cause of the crash, including pilot fatigue (the captain was well over his duty limit due to the aircraft being delayed), the landing lights at Prestwick being out of action due to repair and the First Officer either not hearing a command from the Captain for landing lights (which may have helped judge the low cloud base) or mistakenly hitting the flaps, causing the aircraft to stall.^[7]
• 26 March 1955: The no. 3 engine and propeller tore loose from the wing, causing severe control difficulties. The aircraft was eventually ditched 35 miles off the Oregon coast. The Boeing, named "Clipper United States", sank after 20 minutes in water of about 1600m deep. There were four fatalities out of the 23 occupants, including two of the crew.
• In April 1956, Northwest Orient Airlines Flight 2 ditched into Puget Sound after the flight engineer mistakenly failed to close the cowl gills on the plane's engines, an error attributed to confusing instrument layout. Although all aboard escaped the aircraft after a textbook landing, four passengers and one flight attendant succumbed either to drowning or to hypothermia before being rescued.
• In October 1956, Pan Am Flight 6 ditched northeast of Hawaii, after losing two of its four engines. The aircraft was able to circle around USCGC Pontchartrain until daybreak, when it ditched; all 31 on board survived.
• Clipper Romance of the Skies, Pan Am Flight 7, left San Francisco on November 8, 1957, headed for Hawaii with 38 passengers and 6 crew. The 377 suffered a mechanical failure that may have been sabotage, and crashed around 5:25 p.m. in the Pacific Ocean. There were no survivors. 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.
• 2 June 1958: A Pan Am Boeing Stratocruiser, "Clipper Golden Gate" (registration N1023V), 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. 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.
• 10 April 1959: At the conclusion of a flight from Seattle to Juneau, Alaska, a Pan Am Boeing 377, named "Clipper Midnight Sun" (registration N1033V), undershot on finals and collided with an embankment. The aircraft caught fire and was destroyed but all passengers and crew survived.
• 9 July 1959: A Pan Am Boeing Stratocruiser, "Clipper Australia" (registration N90941), was on finals for Tokyo 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. Zero casualties.
• August 1967: a ground collision with Stratocruiser N402Q; the aircraft was damaged beyond repair.
• 12 May 1970: The Aero Spacelines 377MGT was a converted Boeing Stratoliner. 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.

Variants[link]

^{[8][9][10][11][12]}

377-10-19

Prototype Stratocruiser. Only one example constructed. Was later brought up to 377-10-26 standard and sold to Pan American World Airways in 1950.

377-10-26

20 aircraft delivered to Pan American World Airways with round windows and a rear galley.

377-10-26S

10 aircraft refitted with more powerful engines and a larger fuel capacity for transatlantic operations. Called the "Super Stratocruiser".

377-10-28

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

377-10-29

Eight aircraft originally 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.

377-10-30

Ten Aircraft built for Northwest Orient Airlines with all rectangular windows and an aft galley.

377-10-32

Six aircraft built for the British Overseas Airways Corporation (BOAC). Featured a midships galley and all cabin windows were circular.

377-10-34

Seven aircraft built for United Air Lines. Featured rectangular windows for the main cabin and circular windows for the lower cabin. Aircraft were later sold to BOAC.

377F

Freighter conversion.

377M

In the early 1960s, the Israeli Air Force wished to upgrade to the C-130 Hercules which could lift larger payloads, but it was expensive and sales were embargoed by the United States. Instead, Israeli Aircraft Industries at Ben Gurion International Airport offered to modify Boeing 377 Stratocruisers it had with a stronger cabin floor which could handle cargo, plus a C-97 military Statocruiser tail section, which included a clam shell cargo door. These were dubbed Anak (or Giant in Hebrew) and served starting 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 hosereel refuelling pods. Two others were ELINT-platforms for electronic reconnaissance, surveillance and ECM-missions (ECM-Electronic Counter Measures). These were later joined by four KC-97G's with the flying boom system.

Aero Spacelines Guppy[link]

The Pregnant Guppy heavy lifter.

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.^[1] They had an extension to the top of the fuselage to enable them to carry large aircraft parts between manufacturing sites.

The first of these was the Pregnant Guppy, followed by the Super Guppy, and finally the Mini Guppy. The Super Guppy and the Mini Guppy were both powered by turboprop engines.

Aero Spacelines 377PG Pregnant Guppy

Conversion done to 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 constructed 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, wings stretched by 23 feet, and four Allison 501-D22C turboprops. There were four built, and they were used by Airbus to transport aircraft parts between its factories. In the 1990s Airbus retired them due to rising operational costs and they have been replaced with Airbus Belugas.

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.

Specifications (377)[link]

Data from Airliners of the World^[13]

General characteristics

• Capacity: Up to 100 passengers on main deck plus 14 in lower deck lounge; typical seating for 63 or 84 passengers or 28 berthed and five seated passengers.
• Length: 110 ft 4 in (33.63 m)
• Wingspan: 141 ft 3 in (43.05 m)
• Height: 38 ft 3 in (11.66 m)
• Wing area: 1769 ft² (164.3 m²)
• Empty weight: 83,500 lb (37,876 kg)
• Max. takeoff weight: 148,000 lb (67,133 kg)
• Powerplant: 4 × Pratt & Whitney R-4360-B6 Wasp Major 28-cylinder radial engines four-bladed propellers, 3,500 hp (2,610 kW) each

Performance

• Maximum speed: 375 mph (603 km/h)
• Cruise speed: 301 mph (483 km/h)
• Range: 4,200 mi (3,650 nmi, 6,760 km)
• Service ceiling: 32,000 ft (9,800 m)
  

• Max cruise: 340 mph (547 km/h)

See also[link]

Related development

• B-50 Superfortress
• C-97 Stratofreighter
• Pregnant Guppy
• Super Guppy
• Mini Guppy
  

Aircraft of comparable role, configuration and era

• Canadair CL-44
• Douglas DC-7
• Lockheed L-188 Electra
• Lockheed Constellation
• Lockheed L-049 Constellation
• Lockheed L-649 Constellation
• Lockheed L-749 Constellation
• Lockheed L-1049 Super Constellation
• Lockheed L-1649A Starliner
• Lockheed Constitution
• Tupolev Tu-70
  

References[link]

Notes

Bibliography

• Wilson, Stewart (1999). Airliners of the World. Fyshwick, Australia: Aerospace Publications. ISBN 1-875671-44-7. 
• Boeing 377 – Stratocruiser A very comprehensive enthusiast page on the type
• The Aviation History On-Line Museum – Boeing 377 Stratocruiser
• California Classic – The Boeing Model 377 Stratocruiser
• Air Disaster, Vol. 4: The Propeller Era, by Macarthur Job, Aerospace Publications Pty. Ltd. (Australia), 2001 ISBN 1-875671-48-X

External links[link]

• Stratocruiser article excerpts
• Anak (Israeli Boeing 377)
• Aviastar Virtual Aircraft Museum