Boeing has begun assembling 737NGs at a rate of 38 airplanes per month, the company announced Tuesday. Over the past two years, monthly production of the 737 has risen more than 20 percent, from 31.5 to 38 airplanes. Plans call for the rate to increase again to 42 airplanes a month next year.

Mechanics completed loading initial parts of the spars—internal support structures in the wings—into an automated spar-assembly machine for the first airplane undergoing assembly at the new rate. Fabrication of the spar marks the first step in building the wings and the start of major manufacturing for an airplane.

“The first spar load serves as the defining moment for our latest rate break, and the 737 team did it as planned, on schedule,” said Beverly Wyse, vice president and general manager of the 737 program. “We have more hard work ahead of us, but we are well on our way to another successful production rate increase.”

Boeing expects to deliver the first 737NG built at the new rate in the second quarter of this year.