As the 737 Max 8 approaches the airworthiness certification milestone, Boeing’s narrowbody hub in Renton, Washington, enters a frenetic period of activity, with the first 737 Max 9 test aircraft nearing first flight in early March, a proposed 737 Max 10 wrestling with a key design decision, a multi-airline entry into service looming in the second quarter and a production ramp-up to yet another record-breaking level slated to start in May.

The first member of the re-engined 737 family is three flight tests short of completing a year-long campaign to gain US Federal Aviation Administration, says Boeing vice-president and general manager Keith Leverkuhn. Boeing has already handed over most of the test records to the FAA, keeping certification of the single-aisle on track for the first quarter and entry into service withNorwegianin May.

AirticketsONLINE

“We are anticipating certification of the airplane within a matter of days or weeks,” Leverkuhn says.

The 737 Max family is still being reshaped more than five years after Boeing unveiled the update to a product that celebrates the 50thanniversary of first flight on 9 April, with both the lower- and upper- members of the family getting a second look. Last July, Boeing announced a 1.93m (76in) stretch of the originally designed 737 Max 7, adding two more rows of seats to the economy cabin.

Taking a page from that revision, Boeing’s product development staff is now discussing with airlines a proposed 737 Max 10, with a recently finalised, 1.68m stretch compared to the slower-selling 737 Max 9, adding two rows of economy class seats.

“So far we’re getting some good responsese from the airlines we’re talking to,” Leverkuhn says.

A sticking point for the designers remains how to manage the heavier loads on the landing gear. In selecting the 1.68m stretch, Boeing rejected concepts requiring more elaborate changes to compete with the faster-selling Airbus A321, including a switch to a larger engine. The proposed 737 Max 10 retains the 28,000lb-thrustCFM InternationalLeap-1B and accepts a slightly higher maximum take-off weight, Leverkuhn says. The challenge now is designing a landing gear that can absorb the higher loads while fitting into the existing wheel well with minimal design changes.

Boeing has been evaluating multiple “good ideas”, including a shift from the 737’s traditional oleo strut to a trailing link landing gear design, Leverkuhn says. A key criteria in the final decision later this year will be the inherent reliability of the landing gear design, he adds.

As sales and engineering efforts continue on the 737 Max 10, Boeing is wrapping up final systems installation of the 737 Max 9. During a 13 February factory tour, Boeing displayed a fully assembled aircraft, with test instrumentation and systems installation still in progress. First flight is expected in April, followed by a nine-month flight test campaign by two test aircraft, Leverkuhn says.

The 737 Max remains on the schedule that Boeing outlined more than five years ago, despite a series of interior design changes. The aircraft’s performance has lived up to expectations, but concerns developed about the ability of machinists to produce the design amidst escalating production rates. So Boeing made several changes to make the aircraft easier to build, including re-routing how portions of the wiring is installed, Leverkuhn says.

With five new or proposed single-aisle designs, including a 200-seat variant of the 737 Max 8, in development, it is possible to overlook that Boeing is preparing for a historic rate increase in May, which is often regarded as the most challenging task for any production programme. The “rate break” will increase monthly output in Renton from 42 to 47 737s later this year. Keeping that rate increase on track while integrating the 737 Max into the assembly flow drove Boeing to make the design changes.

“Looking at rate, we had to do it. We had to make these hard decisions early. What we didn’t want to do is stumble as we went to our rate build-up,” Leverkuhn says.

Boeing expects that 10-15% of 737 deliveries in 2017 to involve re-engined models, representing roughly 50-75 tail numbers to multiple airlines. That has caused Leverkuhn’s team to “open the aperture” in preparing airlines to absorb the 737 Max. Rather than concentrating on a single launch customer, such as the 787-8 delivery toAll NipponAirways in 2011, Boeing is preparing multiple airlines at the same to launch operations with the 737 Max, Leverkhuhn says.