The fourth of seven airplanes that have so far rolled off the Boeing narrowbody assembly line in Renton, Washington, the Boeing 737 Max 8 on display here is taking a brief break from ETOPS and function and reliability (F&R) testing. The other three test articles continue to collect flying hours toward expected certification in the first half of next year.

Speaking with a group of reporters in front of the airplane on the eve of the show, Boeing 737 program head Keith Leverkuhn revealed that the four test airplanes have now flown some 800 test hours during just over 300 flights, including a pair of so-called “fly-turn-fly” days, designed to more realistically simulate scheduled operations. The exercise, said Lerverkuhn, reflects Boeing’s “Right at First Flight” effort, which arose out of its stated intent to ensure the same 99.8 percent dispatch reliability rate the 737NG now delivers. “I’m happy to say there was one squawk on the airplane, so that was good,” said Leverkuhn. “We took a delay on one of our fly-turn-flies, but it was our documentation; it wasn’t the airplane.”

CFM International holds one of the keys to helping Boeing meet its dispatch reliability goal—a materials and aerodynamic upgrade to the low-pressure compressor in the airplane’s Leap-1B turbofans. Leverkuhn said he expects delivery of the first pair of engines—equipped with the so-called Block 2 modification—in about four weeks. Those engines, said Leverkuhn, will likely go on the third flight-test airplane. Number 2 will get the next pair. “There’s a very small test program necessary for us to validate what that’s about, and then we’ll just continue on with our regular certification,” he noted.

Leverkuhn also revealed the existence of a few “hot spots” in the supply chain, as it prepares for what he called a steep rate ramp in Renton, where Boeing now builds 42 NGs a month on two lines. “It’s currently a go-slow line, but it’s not going to be a go-slow line for very long,” he said, referring to the third line now dedicated to the Max. “So we’re going to get that line up to rate before we introduce the Max onto either of the other two lines.”