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Safe and sound as it cruises through the barrier ...

By JAMES WALLACE

SEATTLE POST-INTELLIGENCER REPORTER

Several years from now, you may be flying along in The Boeing Co.'s "sonic cruiser," traveling just under the speed of sound at 44,000 feet, when a big gust of wind or jet-stream surge pushes the plane a little faster.

What happens? The sonic cruiser could break through the sound barrier.

It's a very real possibility that has not escaped the attention of the engineering team that is hard at work on Boeing's project to build a new commercial jetliner that would cruise at between Mach .95 and Mach .98. (The speed of sound above 36,000 feet is 661 mph.)

That's about 15 to 20 percent faster than today's jetliners. And because the sonic cruiser would fly just shy of the speed of sound, some extra margin of safety would have to be built into the design so the jet could handle speeds above the sound barrier.

When it comes time for the plane to be certified for service by the Federal Aviation Administration, the sonic cruiser would likely have to demonstrate it could safely fly much faster than Mach 1, reaching the kinds of speeds it might encounter in an unexpected dive, for example.

John Roundhill, who led Boeing's product development team responsible for the sonic cruiser and who is now out marketing the plane with airlines, said at last month's Paris Air Show that extensive research shows that a sonic boom created by the sonic cruiser flying at Mach 1.05 would dissipate long before it reached the ground.

That's an important point.

Because of the sonic boom it creates, the Concorde is restricted to flying supersonic only over the ocean.

Boeing is already having to defend the sonic cruiser from critics worried that it would burn more fuel than conventional jetliners and damage the environment.

Boeing says that's not the case, and asserts that the emissions from more advanced engines on the sonic cruiser would actually be cleaner than those produced by today's jetliners.

The fastest commercial jetliner, other than the Concorde, is Boeing's 747. It can cruise at Mach .85. Most other commercial jets cruise closer to Mach .80.

Boeing's venerable jumbo jet reportedly hit Mach 1 during certification testing more than three decades ago.

Pilots will sometimes push the 747 to around Mach .90 for short periods.

It's conceivable that future pilots of the sonic cruiser would also give the plane a little nudge in cruising speed from time to time, pushing it through the sound barrier.

In fact, Alan Mulally, the boss of Boeing's commercial airplane operations, said the sonic cruiser's breakthrough design actually has two "sweet spots."

And one is just above the sound barrier.

Aerospace Notebook is a weekly feature by P-I aerospace reporter James Wallace. He can be reached at 206-448-8040 or jameswallace@seattlepi.com

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