How much can a jet withstand?

Published 6:55 pm Friday, June 19, 2009

EVERETT — Under gray skies and light rain, a 767 barrels down the runway at Paine Field and lifts into the air.

A few minutes later, the plane returns, appearing as if it will land again on the runway across from the Boeing Co.’s gigantic factory in Everett. Almost as soon as the jetliner touches down, it reaches for the sky again.

It’s one in the array of tests that all Boeing aircraft undergo before being handed over to an airline — whether it’s the 1,400th 747 or the 780th 777.

If jets whose brothers and sisters have demonstrated a good history in service go through these kinds of hoops, imagine the testing for a new jet from a brand-new aircraft program.

Flight testing allows Boeing to determine whether the 787 will perform as it was designed, said Barbara Cosgrove, vice president of flight test operations for Boeing, in late April. Boeing will have eight to nine months to see how the Dreamliner responds under a variety of flight scenarios.

Flight tests make up only about 10 percent of the overall documentation that Boeing submits to the Federal Aviation Administration for its approval, said Boeing’s Mike Delaney, at a flight test briefing in April.

But flight tests are among the most high-profile of the tests that a new aircraft undertakes before entering commercial service.

Airplanes don’t always fly in ideal conditions. Therefore, jet makers and regulators ensure airplanes can withstand the worst flying conditions, from low temperatures to high altitude.

Boeing’s six test aircraft will undergo both ground and flight testing as part of the FAA certification process.

The four test 787s equipped with Rolls-Royce engines will log a total of 2,430 hours of flight and 3,100 hours of ground tests, said Frank Rasor, director, flight test operations. The two test Dreamliners with General Electric engines will undergo more than 600 hours on the ground and in the air.

Because Boeing conducts several tests simultaneously, the company can check off several hours’ worth of tests in a single outing.

But some tests will stand out, like the first time that Boeing tries to land its 787 in heavy crosswinds or takes off after striking its tail on the runway.

Boeing already has decided which test plane will be subjected to different tests. For example, the first Dreamliner will undergo flutter testing, which essentially monitors the aircraft’s vibration in flight.

“Airplane two is our fuel systems airplane,” Rasor said.

Boeing engineers made certain assumptions about how much load the 787’s wings could withstand during flight, Rasor said. Sensors installed on the third test plane will allow Boeing to verify those assumptions.

The company will see how the fourth test 787 performs at high speeds. Aerodynamic performance will be put to the test on airplane five while six will help the company understand how the 787 responds in lightning. The company won’t specifically try to have its 787 struck by lightning, said Mike Delaney, 787 lead engineer.

But Boeing planes have been struck by lightning in each previous test program, Rasor said.

Over the course of the test program, Boeing will fly its test planes in both extreme heat and extreme cold. The company initially planned to certify its 787 to minus 35 degrees Celsius. But Transport Air Canada has asked for a minus-55-degree certification, Rasor said. Boeing has designed ice shapes to attach to the aircraft to test how the plane will perform under extreme icing conditions.

“We’ve been able to simulate the worst-case icing conditions without getting into those scenarios,” Rasor said.

The company is looking at conducting high-altitude tests on the 787 in places like Bolivia, China or Japan, he said.

Lastly, to meet Extended-range Twin-engine Operational Performance Standards, known as ETOPS, Boeing will log in long hours consecutively on its 787.

“We try to get a lot of hours in on it,” Rasor said.