Stratoliner Ditches
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 The Stratoliner touched down slightly right wing low in a level pitch attitude with the gear extended, and didn't flip over. One observer believed the final airspeed was about 110 mph. The aircraft remained afloat, and the crew walked from the wing onto a boat. It settled further before being recovered. |
The aircraft belongs to the Smithsonian Institution and was to be delivered in July 2003 to the National Air & Space Museum's new Dulles annex. Boeing officials are assessing the condition to decide how to repair the aircraft, ranging from a restoration to flightworthy condition to a cosmetic fix for static display. The S-307 was restored by volunteers and the Boeing Co. starting in the early 1990s, and made its debut at Oshkosh last year (AW&ST Aug. 13, 2001, p. 47). It is the only remaining Stratoliner of 10 built.
THE AIRPLANE TOOK OFF from Boeing Field at about 12:30 p.m. local time and flew north to Paine Field about 25 mi. away, where it made a full-stop landing. Shortly after liftoff from Paine, the No. 3 (inboard right) engine had a momentary surge and the crew decided to return to Boeing Field, according to a crew interview by the NTSB.
On approach, the left landing gear would not fully extend by the normal electric drive. The crew broke off the approach and the flight engineer at the radio station left to manually crank the gear down, which was successful after several minutes. The plane headed back to Boeing Field when the low-fuel-pressure light for the No. 3 engine illuminated and it lost power. The crew feathered that propeller, but then the Nos. 4, 1, and 2 engines successively lost pressure and power. The crew decided to ditch the airplane in Elliott Bay. The impact was at about 1:05 p.m., 35 min. after the flight started at Boeing Field.
All the crew are from the Boeing flight test department. The two pilots were Richard Nelson, 767 chief project pilot, and Michael Carriker, the Sonic Cruiser project pilot. The last time the S-307 flew was in August, seven months earlier, one observer said.
 Damaged Stratoliner is being cleaned and examined in a hangar near Boeing Field. Note No. 3 propeller in feathered position--it was the first engine to die. |
In the original fuel system, each engine can draw from any of three fuel tanks on its wing. There is a hand pump to supplement the engine fuel pump. Later versions of the B-17 bomber, upon which the S-307 is based, changed the plumbing considerably, and it is not clear if the system was modified during restoration.
BOEING OFFICIALS would not say what the fuel load was for takeoff, but one thought it was fueled on the day of the flight. The NTSB drained the fuel and saltwater from the tanks to see how much fuel was left.
The landing gear were ripped off and some of the motor mounts were broken. The silk fabric interior was probably ruined by the water and leaking fluids, and saltwater corrosion is a major concern. Divers recovered the landing gear.
See Also:
Description and illustration of fuel system
Museum officials worry about future of flying aircraft
KMOV St. Louis Channel 4 coverage and video of the crash
NTSB preliminary accident synopsis
Boeing 307 sites:
Aviation History Online Museum
Aviation Safety Network (list of 307 accidents)
AOL, with Microsoft Flight Simulator model
April 8, 2002
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DESCRIPTION OF FUEL SYSTEM
Boeing claims that the NTSB won't let them talk about the Stratoliner so we present our best guess at how the fuel system works. This is based on the fuel system schematic from the original aircraft, descriptions of how it may have been modified, and a photograph of the flight engineer's panel on Boeing's restored aircraft. The original 1,700-gal. system has three tanks in each wing -- a 425 gal. main tank, and 212.5-gal. inboard and outboard auxiliary tanks. Each engine on a wing can draw from any of these three tanks via a fuel selector on the flight engineer's panel. A one-in. tube provides gravity crossfeed between the left and right main tanks, with valves at each side of body and a drain inbetween. From the selector valve, fuel goes through a hand fuel pump, a strainer, the engine-driven fuel pump, a flowmeter, and then to the carburetor, where fuel pressure is sensed. A crossfeed valve can connect the two engines on a wing at the engine-driven pump output.
One description of subsequent modifications is that electric boost pumps were added, and this may be born out by a photograph of the pilots' overhead panel, where there appear to be boost pump switches on the right side. Another description says the aircraft were updated with B-17G bomber wings after World War 2 but these had a considerably different fuel system and the flight engineer's panel on the restored aircraft, N19903, is clearly representative of the original 307 system. It may be that just TWA's 307s were converted, and not PanAm's. We conclude that N19903 has the original 307 system with electric boost pumps added. This would seem to be the most necessary modification in a high-altitude aircraft where fuel vapor lock could be a problem. The flight engineer's panel has the four engine fuel selectors with red handles on the left, with positions for Off, Main, Outboard Extra (auxiliary), and Inboard Extra tanks. To their right are the three fuel quantity gauges for the main and inboard and outboard extra tanks, with dual pointers for left and right wings.
It should be noted that the position of the inboard and outboard gauges appear to have been reversed during the restoration. A "before" photograph shows the outboard gauge in the middle and the inboard gauge at bottom, while the "after" photo shows the opposite. However, other gauges on the panel were rearranged in the restoration, though in a more major way than just flipping two otherwise identical indicators. The fuel pressure and flow gauges are at upper right, and the red lights above them are probably low fuel pressure warnings for the four engines. The fuel pressure lights and gauges are repeated on the pilots' front panel . The crossfeed valves that connect the two engines on a wing are on a separate panel at the extreme right of the picture. The gravity crossfeed valves that connect the left and right main tanks may be the two red handles grafted on at the extreme left of the flight engineer's panel. The B-17G fuel system uses the same basic fuel tanks but connects them differently. Each engine can feed from only one tank and an enhanced tank crossfeed system moves fuel around. The outboard engines draw from the 425-gal. main tanks, and the inboard and outboard auxiliary tanks are plumbed together to make single 425-gal. tanks to feed the inboard engines. There is no confusion as to what tank each engine is drawing from. A crossfeed pump moves fuel across the fuselage in either direction and can be directed at either tank in each wing. Extra tanks add capacity, but they feed into the above-mentioned tanks. See Also: Stratoliner Ditches After Losing Fuel Pressure Museum officials worry about future of flying aircraft KMOV St. Louis Channel 4 coverage and video of the crash NTSB preliminary accident synopsis Boeing 307 sites: Aviation History Online Museum Aviation Safety Network (list of 307 accidents) |
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