said late Friday that its 737-10, the largest jet in the 737 Max family, completed its “successful” first flight, kicking off a test program for the plane. The plane is expected to begin service in 2023 after testing and certification. “The 737-10 is an important part of our customers’ fleet plans, giving them more capacity, greater fuel efficiency and the best per-seat economics of any single-aisle airplane,” said Stan Deal, chief executive of Boeing’s commercial airplanes unit. The 737-10 can carry up to 230 passengers, with environmental improvements such as fewer carbon emissions, and less noise. Shares of Boeing were flat in the extended session Friday after ending the regular trading day 0.8% lower. Boeing flagged a new, electrical-related problem with 737 Max jets in early April. The Max jets were grounded for nearly two years following two deadly crashes in late 2018 and early 2019 connected to a faulty anti-stall feature.