The sight of a passenger jet performing stunts might terrify you, but it shouldn't. The Boeing 737 MAX is the first new plane of Boeing’s second century of existence, but before it can enter service, it has to prove itself. The 737 is a Seattle stalwart—the best-selling commercial jet ever—but that doesn't mean it can afford to skimp on evolution.

That's why Boeing has built the 737 MAX, a new take on the jet that's 14 percent more efficient and 40 percent quieter than the outgoing version. But before airlines can cram you into the thing, Boeing's got to prove it's airworthy in just about any situation.

The 737 MAX will compete directly with the Airbus A320neo, both fighting for dominance of the single aisle passenger jet market.

The MAX left the ground for the first time in January, in front of an applauding crowd. Test pilot Captain Ed Wilson treated it gently on that initial flight. He didn't even retract the wheels, in case he needed to return to earth on the double. "It was a little nerve wracking,” he says, as he shows us around the redesigned cockpit.

Now the audience is gone and the test pilots have forgotten those gentler days. Boeing has rigged up four 737 MAX aircraft with a bevy of instruments and is busily running them through endless tests and checks. Pilots push the speeds to the limit, head to Bolivia for high altitude testing, and even try to fly with missing winglets.

We went aboard to see how it's done.