Guy Norris With system and software enhancements for retrofit into all MAX versions, 737-10 test and certification is more than sum of its parts.
Guy Norris
The longer main gear incorporates a telescoping oleo-pneumatic strut with a levered component for extra height. Credit: Chris Edwards/Woodys Aeroimages
First flights are a major event in the life of any aircraft, but for Boeing the June 18 test debut of the 737-10 carried extra significance as a symbol of resurgence for both the MAX program and the wider company.
At 143 ft. 8 in. long overall—compared to just over 138 ft. for the 737-9—the 737-10 is the longest, and likely final, derivative of Boeing’s storied twinjet family. Although not scheduled to enter service until 2023—more than two years later than originally planned—the rebaselined development and certification of the -10, in parallel with the 777X, constitutes a tightly scrutinized test case of its newly defined relationship with regulators.
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Seating up to 230, the 737-10 embodies all that has been learned and overcome in the fight for the recertification of the MAX family and its return to service. In addition to incorporating features unique to the -10, such as an all-new main landing gear to accommodate the longer fuselage, the latest derivative also includes wiring hardware and system software upgrades representative of a “block change” standard for all future MAX variants.
From a broader program perspective, the start of -10 flight testing represents an encouraging boost as 737 production begins to ramp back up toward the company’s target of 31 aircraft per month by early next year. The campaign also coincides with a significant rebound in the delivery of stored and newly manufactured aircraft—including the initial 737-8 200s. Also waiting in the wings are first deliveries of the 737-7, certification of which was imminent when the MAX was grounded in March 2019.
The 737-10 is therefore seen within Boeing as emblematic of a program that is fast returning to the original game plan set before it was struck by the MAX accidents in 2018 and 2019 and the COVID-19 pandemic in 2020. The -10 is a key player in Boeing’s campaign to regain market share lost to Airbus with the A321. Having knowingly sacrificed range for capacity for the -10, Boeing believes the 3,300-nm-range aircraft still plugs most of the product gap the company’s more loyal customers had asked to have filled in the 2010s, when Airbus hatched plans for longer-range versions of the competing A321neo.
With almost 500 firm orders in the backlog, compared to 240 orders and commitments when launched at the 2017 Paris Air Show, it appears operators concur with Boeing’s contention that what the -10 lacks in range it will more than make up for in capacity and competitive operating costs. Boeing backs up this notion by pointing out that the bulk of -10s will be operated on U.S. transcontinental routes and shorter international Asia-Pacific sectors.
According to the Aviation Week Network Fleet Discovery database, at least 17 airlines and leasing companies have ordered the aircraft, the largest single customer being VietJet Air with 106, followed by United Airlines (92) and Lion Air (50). Other key operators include Gol and Virgin Australia, with 25 each, Tui Travel (21) and Copa (15). The launch group also includes three Chinese operators: Okay Airways, Donghai Airlines and Xiamen Airlines, which have ordered 23 aircraft between them.
Although the aircraft-maker has not provided details of the planned test program or specifics of how new features such as the landing gear or augmented angle-of-attack (AOA) system will be evaluated, the certification effort is expected to be longer and more intense than for previous 737 derivatives. The flight-test phase began on June 18 when the first -10, and the fourth version of the MAX series, completed a 2-hr. 30-min. test mission in picture-perfect weather over Washington state.
Flown by 737 Chief Pilot Jennifer Henderson and Boeing Commercial Airplanes Chief Pilot Jim Webb, the aircraft—designated 1G001—departed to the north from Runway 34 at Boeing’s Renton, Washington, facility at 10:07 a.m. local time. After passing Everett and climbing to 17,500 ft. the aircraft was flown toward eastern Washington for tests of initial airworthiness, handling qualities, systems and flight controls at altitudes up to 23,000 ft. and speeds up to 345 kt.
Stretched to within inches of the length of the first Boeing 707 model, the initial 737-10 landed for the first time at Boeing Field on June 18. Credit: Chris Edwards/Woodys Aeroimages
The aircraft then turned south and descended to 15,000 ft. at 280 kt., where slow-speed handling tests were conducted close to the Oregon border. The crew then conducted a touch-and-go at Moses Lake before returning to Seattle. Further handling checks were performed en route, including an approach to stall at 15,000 ft. The aircraft returned safely to Boeing Field, where it touched down on Runway 32 Left at 12:39 p.m.
Although much of the flight resembled a standard Boeing “B1” initial production test-flight profile, some maneuvers later in the mission are thought to have exercised a recently introduced software-based synthetic AOA augmentation system. Adopted primarily under the direction of the European Union Aviation Safety Agency as part of the MAX return-to-service review, the AOA integrity enhancement system in the -10 builds on technology used in the 787 air data system. Providing a backup to the aircraft’s pair of standard aeromechanical AOA sensors, the system calculates angle of attack primarily from inertial data.
Boeing has not yet provided details of the air data enhancement. “We looked at an enhancement to the air data indication system. We are working on that as we speak,” Stan Deal, president of the company’s Commercial Airplanes unit, said after the flight. “We’re going to take our time on this certification. We need the time to do that, to allow the regulators to be on the airplane.”
Another focus for the 737-10 test campaign is the aircraft’s revised, taller main landing gear design, which combines a telescoping section to shorten the leg and a semilevered lower element. The combined design raises the body by 9 in. and moves the aircraft takeoff rotation point aft—yet still fits within the existing MAX wheel well. The new gear is the key enabler of the 737-10’s 66-in. fuselage extension, which is made up of a 40-in. plug in the forward fuselage and 26 in. aft.
In common with previous major derivative developments, Boeing is initially dedicating two aircraft to the 737-10 test effort, with a third cabin-configured aircraft widely expected to join the later stages of the certification campaign for preservice entry reliability and functionality tests. The second aircraft, 1G002, is scheduled to join the test program later this summer.
