Boeing Works On 737-7 And 737-10 Approvals Amid Strict FAA Scrutiny

Boeing’s progress on getting the last two members of the 737 family approved by the FAA remains elusive as the manufacturer labors to meet the agency’s revised certification-program expectations.

Flight testing on the 737-7—the smallest version of the planned, four-member 737 MAX family—wrapped up late last year. Launch customer Southwest Airlines said as recently as January that Boeing was targeting the end of the first quarter of 2022 for initial deliveries. 

But a March 24 regulatory filing confirmed that the 737-7 is one of three programs “currently conducting amended type certification (ATC) testing,” along with the 737-10 and 777-9.

“The flight-test program is an element of the overall airplane development program, leading up to the FAA’s granting of the ATC,” Boeing tells Aviation Week. “The 737-7 completed its flight-test program last year, and we continue to work with the regulator to meet all the necessary requirements for ATC.”

A source close to the program says certification is now targeted for the second half of 2022.

Once slated to enter service in 2019, the 737-7’s certification pace slowed in response to two main factors: the 737 MAX family’s grounding following two fatal 737-8 accidents and the outbreak of the COVID-19 pandemic. The FAA lifted its grounding of the MAX family in November 2020 after 21 months, and deliveries of 737-8s and 737-9s resumed several weeks later. 

Aside from a shortened fuselage, the 737-7 essentially replicates the two models in service, including the modified Maneuvering Characteristics Augmentation System (MCAS) flight control law software to compensate for design flaws that investigators determined were central to both accident sequences. 

Much of the certification work on the variant was done before the grounding, and neither the FAA nor Boeing will comment on the certification program’s specifics. Multiple sources with knowledge of the situation say that Boeing is still adjusting to the FAA’s new, more stringent approach to scrutinizing certification projects, and missed milestones in the 737 MAX and 777X programs illustrate the point (AW&ST Oct. 11-24, 2021, p. 22).

In some cases, work once delegated to Boeing is now done by FAA personnel—part of changes mandated in a 2020 law that targets certification reform based on lessons learned from the 737 MAX saga. In other cases, the agency is asking for more data to back up deliverables and more detailed schedules and test plans, for instance (AW&ST July 12-25, 2021, p. 14). Projects are not moving until Boeing provides them, says one government source. 

“They have to show their work,” the source says.

Recent changes in FAA leadership will not alter its approach. Former Administrator Steve Dickson, who left the agency at the end of March after 2.5 years at the helm, is credited with setting the agency’s new-world-order tone with Boeing. Billy Nolen, who leads the agency’s safety branch, stepped in as the interim agency chief on April 1 while the Biden administration searches for a permanent replacement. One of Nolen’s first external meetings was with Stan Deal, head of Boeing Commercial Airplanes. Among Nolen’s messages to Deal, according to a source with knowledge of the meeting: Nothing about the relationship reset between the FAA and Boeing will change on his watch.

The 2020 law that mandated changes to the FAA’s certification is acutely troublesome for the 737-7 and -10. A provision in the bill prohibits the FAA from issuing a type certificate to a transport category aircraft after Dec. 27, 2022—two years after it became law—unless the design includes a flight crew alerting system. The 737 MAX’s certification basis included exemptions from aspects of FAA’s flight crew alerting rules that have evolved to require modern flight decks to provide pilots with more sophisticated cues and troubleshooting guidance.

The older 737 versions were developed before the rules were in place and do not meet them. The FAA’s decision was based on Boeing’s argument that complying with the updated regulations would add unnecessary expense and pilot-training requirements to an already safe baseline design. Boeing would face similar hurdles, not to mention significant delays in getting the new variants approved if forced to modify the 737 MAX design to incorporate the systems.

The provision was a symbolic stance by lawmakers—the two-year grace period was selected to allow both the 737-7 and 737-10, the only aircraft affected by it, to earn FAA approval. But the new, more rigorous certification process combined with Boeing’s apparent inability to meet the agency’s requests in a timely manner have made the deadline an issue, particularly for the 737-10. 

Rep. Peter DeFazio (D-Ore.) said April 6 that the “grace period should not be extended,” while Sen. Maria Cantwell (D-Wash.) told The Seattle Times in late March that an extension was possible if deemed technically prudent. 

The FAA’s decision to grant a partial exemption during the aircraft’s design process signifies its stance from a safety standpoint, and agency sources tell Aviation Week it has not changed.

Without an extension, Boeing seemingly faces two choices: modify the designs so they comply with the latest rules, likely adding new, costly pilot-training requirements in the process; or terminate the affected programs. 

Without a 737-10, the company could have even more incentive to examine a new narrowbody to compete against the Airbus A321XLR.

“If they don’t get the waiver, then it’s time for that calculation—incremental costs related to certification, versus benefits and risks of transferring that cash” to a new program, says Richard Aboulafia, managing director at AeroDynamic Advisory. But, he adds, the motivation gained from not having the largest 737 MAX variant in service may not be enough to alter Boeing’s timeline for product development. 

“Given the reluctance the company has shown to launch a clean-sheet, I’m not sure how killing the MAX 10 would suddenly make it likely,” Aboulafia says. “If they’re balking at a 797 launch, I’m not sure how the modest transfer of MAX 10 certification cash would make much difference.”

The congressional deadline combined with the FAA’s new show-me approach place significant hurdles in the 737-10’s path to a 2022 certification. The longest variant includes an enhanced angle-of-attack (eAOA) system—an addition required by the European Union Aviation Safety Agency (EASA) as part of its agreement to approve the 737 MAX’s return (AW&ST Feb. 22-March 7, 2021, p. 24). EASA said in its January 2021 report on the 737 MAX return that the eAOA would be “integrated in [the] 737-10 version and retrofitted on the in-service fleet.”

The extent of the changes forced Boeing to reframe 737-10 development and certification as a “block point” change in the baseline configuration. As the most extensive single-aisle certification campaign since the 737 MAX grounding, it is emerging alongside the 777X as the new template for the revised regulatory approval process.

“The -10 is taking the brunt of this [new process], but once the MAX has gone through this—and we have had to rebuild that relationship with the FAA—it should make it easier for the following aircraft,” a Boeing engineer tells Aviation Week.

The eAOA is a synthetic sensor that collects AOA data from five different aircraft parameters and provides a key new safety feature by constantly cross-checking the derived AOA against inputs from the two standard AOA sensors mounted on either side of the aircraft’s nose. Boeing has not disclosed the system’s supplier, but sources with knowledge of the program confirm it is Collins Aerospace.

If the eAOA detects an erroneous signal from either of the standard sensor vanes, it is designed to suppress that input. Faulty AOA data was a factor in both fatal 737-8 accidents. The aircraft’s return-to-service requirements included modifications to add cross-checking between two flight control computers and changes to how MCAS works. Boeing also was ordered to produce several long-lead items, led by the eAOA.

The MCAS, which automatically adjusts the horizontal stabilizer based on AOA data, was added to the 737’s speed trim system to ensure the MAX handled like its predecessor, the 737 Next Generation, during certain low- and high-speed flight profiles. Unneeded MCAS activations triggered by a single faulty AOA sensor played central roles in both accidents.

As part of improvements to clear the 737 MAX to return to service, the FAA mandated changes to the MCAS to ensure that the two existing sensors compare AOA readings before triggering nose-down stabilizer inputs. EASA wanted a third physical sensor but settled for the eAOA.

“We are actively flight-testing the 737-10 and are not commenting on specific technologies, including enhanced AOA,” Boeing says.

Industry sources tell Aviation Week that Boeing completed critical design review of the new feature late in 2021. Boeing spent much of January and February installing the system in the second 737-10 test aircraft, dubbed 1G002, and began ground tests around Feb 28. The aircraft is believed to have begun flight tests of the eAOA as an active part of the flight control system on March 3.

Evaluation of the synthetic AOA system forms only one element of the overall 737-10 flight-test and certification program, which began following the aircraft’s first flight on June 18, 2021. The aircraft, which is 66 in. longer than the 737-9, has an all-new landing gear design and additional hardware and system changes that were required as part of the 2020 recertification of the MAX in the wake of the grounding.

Launched as the 737 MAX 10 at the 2017 Paris Air Show with 240 orders and commitments, the 737-10 was originally due to enter service in 2020. The first aircraft, designated 1G001, was rolled out at Renton, Washington, in the midst of the 737 MAX crisis in November 2019. But following a review of redesigns and pandemic-related development hold-ups, Boeing announced in 2021 that first deliveries will not begin until 2023.

The 737-10 is 143 ft. 8 in. long overall, compared with just over 138 ft. for the 737-9. To enable the fuselage extension, the aircraft incorporates a completely revised taller main landing gear design that combines a telescoping section to shorten the leg and a semi-levered 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.

A critical phase of the recent 737-10 test campaign revolved around the new taller main landing gear design. Recent evaluations also included takeoff performance tests that were conducted at Edwards AFB, California, at the end of February and early March.

The tests, which were conducted using the first 737-10 aircraft, 1G001, included assessments of acceleration parameters, minimum liftoff speeds, rotation rates, and tail contact margins—the latter being a particular validation of the -10’s revised gear design.