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Terry Ford: Terry Ford is an aerospace writer who has many years of experience in the aerospace industry, latterly with British Aerospace, Weybridge, UK
The Boeing 777-200 (Plate 1) entered revenue service in the middle of 1995 and the 777-200 IGW (Increased Gross Weight) version in 1997. The larger 777-300 is scheduled to enter service this year, which is some 33 ft longer than the -200. The -200 IGW is able to carry the same payload as the earlier aircraft over a longer range and therefore requires more fuel. This necessitates some fuel system differences. The -300 has virtually the same fuel system as the -200 IGW but will have a higher payload and gross weight.
Fuel is stored in three tanks; the left main, the centre, and the right main. There is also a surge tank outboard of each main tank, the function of these being to temporarily hold fuel that flows out from the main tanks due to aircraft turns, or to thermal expansion, or overfill. The 777-200 has a dry bay in the centre tank where it passes through the fuselage. Two fuel interconnect tubes keep the fuel load balanced in the two sides of the centre tank. The 777-200 IGW and the 777-300 carry fuel in all of the centre tank. The-200 has a total fuel capacity of 201,700lbs (93,900kg) and the -200 IGW and the -300 can carry 302,900lbs (137,000kg) (Table I).
System features
Ground crews can operate all of the sump drain valves on the 777-200 without opening any access panels. A drain line in the lower part of the centre tank takes the fluid to a drain valve outboard of the wing-to-body fairing. There is an access door in the wing-to-body fairing to drain the 777-200 IGW and 777-300 centre tank sump drain valves.
The fuel quantity indicating system (FQIS) calculates and displays the amount of fuel in the tanks and controls some refuelling functions. It is notable that the Boeing 777 is the first production jet airliner to use an ultrasonic system to measure fuel quantity. This system uses ultrasonic sensors throughout the tanks, these units send signals to a processor which calculates the volume, density, and mass of the fuel. As a back-up to FQIS, measuring...