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20 June 2003
The two Boeing 777-300ER (Extended Range) aircraft are meeting, and often exceeding, expectations as they approach their sixth month of flight-testing. As of 16 June, crews had evaluated takeoff, landing, handling characteristics and fuel mileage tests through 187 flights and 536 hours of flying. Overall, the jets will undergo more than 1,600 hours of flight-testing.
One of the new 777 take-off improvement features, Tail-Strike Protection, helps the longer 777-300ER avoid tail contact with the ground on takeoff. Operating through the fly-by-wire flight controls, the system allows the aircraft to lift off at reduced speed, increasing allowable takeoff weight by 4,000 to 10,000 pounds (1,814 to 4,536 kilograms), depending on airport conditions and aircraft structural limits.
"It's in the primary flight computer," said Boeing Test Pilot, Frank Santoni of the special feature. "It's a function that looks at rate of closure of the tail to the ground during rotation, measuring how fast and at what distance the tail is moving toward the pavement." If it's too fast or too close, the system moves the elevator for slower nose rotation. During abuse takeoffs, where Santoni has deliberately rotated the aircraft early and fast, the system has responded as designed.
"It's doing a superb job, which is testament to our engineering team," Santoni said. "On the 777-300 programme six years ago we did the same takeoff performance tests and contacted the tail about 12 times, which is expected during flight-test. On this programme, we haven't touched it."
The new semi-levered landing gear allows the 777-300ER airplane to lift its nose early during takeoff by shifting the centre of rotation from the main axle to aft axle of the three-axle landing gear truck.
"These two features are independent of each other, but both give our customers the ability to take off on shorter runways or put more payload on the aircraft for the same length of runway," Santoni said.
The General Electric GE90-115B engine will power the 777-300ER. Certification of that engine is under way. Each engine produces 115,000 pounds of thrust, nearly a quarter of a million pounds of total thrust for the aircraft. By comparison, the original 777 had 75,000 pounds of thrust per engine. The additional thrust increases the 777-300ER's maximum take-off weight to 759,600 pounds, almost 100,000 pounds more than the 777-300, with virtually no difference in handling characteristics during takeoff, flight and landing.
That power comes at very little expense. Fuel mileage testing shows a 1% improvement in fuel efficiency over original predictions. Such an improvement can reduce by 106,400 gallons (402,724 litres) annually the amount of fuel one airplane uses. It also increases the aircraft's range by 75 nautical miles (139 kilometers) to 7,495 nautical miles (13,881 kilometres); or it increases payload by 2,400 pounds (1,089 kilograms), passenger or cargo, on a 7,000 nautical mile (12,964 kilometre) flight.
Extended Twin-Engine Operations testing begins in the fall, which will consist of 220 hours of ETOPS flying divided between the two flight-test aircraft. Generally, ETOPS flying will involve engine shutdowns for up to 330 minutes, and various system checks and simulated malfunctions will be flown to ensure the systems are working in the long-range environment.
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