Boeing nears 737 MAX 7, 10 certification with engine anti-ice fix

Boeing may soon be able to fly passengers on its long-delayed 737 MAX variants as it nears the end of a lengthy certification process with safety regulators.

The plane-maker has resolved an issue with the MAX’s engine anti-ice system, a potential design defect that has held up regulatory approval, company leaders said last week.

Separately, Boeing has finalized an enhanced angle of attack sensor system, a sensor that was at the center of two fatal 737 MAX crashes in 2018 and 2019 that killed 346 people. In those cases, an erroneous read from the sensor triggered a new software system, which repeatedly pushed the plane’s nose down and caused the pilots to lose control.

Boeing has made updates to its MAX plane following the fatal accidents and a 20-month grounding, but the updated sensor system was “an IOU from the return to service after the very unfortunate accidents,” said Captain Bill Quashnock, deputy chief pilot for 737 programs.

Boeing tested both new systems on its 737 MAX 10, its largest MAX variant and one of the MAX models that has yet to be certified to fly passengers by the Federal Aviation Administration.

Boeing leaders say they are nearing final regulatory approval for both the engine anti-ice system and the enhanced angle of attack sensor system.

Boeing provided updates on the new systems at a briefing last week before the Farnborough Airshow, an annual industry trade event where manufacturers, suppliers and customers show off products and forge business deals.

Once certified, all newly produced MAX planes will carry the enhanced sensor and the improved anti-ice system. MAXs currently flying will receive upgrades in the coming years.

Meanwhile, Boeing leaders told reporters that the company is wrapping up final certification for three new programs: the MAX 7 and 10 and the 777X family, a set of two passenger planes and one freighter that are meant to be larger and more fuel efficient than its competitors, including Boeing’s 777 fleet.

Boeing expects to complete nearly all certification requirements for both MAX models in the third quarter of this year and receive certification in 2026. It is particularly close to completing 737 MAX 7 certification, its smallest MAX variant, having finished 100% of its required flight testing and submitted 95% of its required deliverables.

The plane-maker has more work to do on the 777X certification program but says it is on track for first delivery in 2027, seven years after it originally intended.

Enhanced angle of attack sensor

The angle of attack, or AOA, sensor measures the angle between the plane’s wing and oncoming air flow. It’s used to assess whether the plane is angled up so much that it is at risk of stalling.

In the case of the two fatal 737 MAX crashes, a single AOA sensor recorded an erroneously high value, triggering a new software system on the MAX plane that aggressively pitched the nose of each aircraft down.

After the fatal crashes, Boeing redesigned that software system, known as the Maneuvering Characteristics Augmentation System, or MCAS, as part of a suite of changes Boeing made in order to return the MAX to the skies, including software and computer updates and pilot training in flight simulators.

Now, the enhanced angle of attack sensor system is meant to “simplify the flight-deck effects” if there is a problem with the sensor, Quashnock told reporters last week.

The new system consolidates multiple signals to pilots into one indicator on the flight deck that reads “AOA fail” and tells the flight crew whether it was the right, left or both sensors.

It will also inhibit the “stick shaker,” which, during the final moments of the fatal crashes, vibrated noisily and added to the flight crew’s workload.

“Our engineers have run all the simulations showing that, for pretty much every conceivable error that we know, the monitors will catch it. You won’t get a persistent stick shaker,” Quashnock said.

Still, because “we did promise the regulators,” Boeing added two switches to allow the pilots to manually inhibit the stick shaker.

The new system will allow the flight crew to continue flying the plane if one AOA sensor fails, unless it is on a flight path that crosses an ocean or keeps the plane far away from any airports. That’s a change from the current system which requires a turnback, Quashnock said.

Once certified, Boeing will begin building the new system into the MAX 7s, 8s, 9s and 10s rolling out of the factory.

The FAA and other regulators will mandate all existing MAX planes already in service be retrofitted with the new system within two years, Quashnock said.

Recently, Boeing has been building its MAX planes with provisions to install the new system, Quashnock said, so the retrofit work will take only about two hours. Older MAX models will be retrofitted over several days.

Boeing doesn’t have a cost estimate for that work.

Engine anti-ice fix

Boeing’s engine anti-ice system heats the inner barrel of the engine pod, also known as the nacelle, to prevent ice from building up in moist, cold air. When switched on, the system blows hot air through ducts from the engine core onto the inlet at the front of the engine.

Since 2023, after Boeing discovered a potential defect with the engine anti-ice system, pilots have had to make sure they turn off the system after emerging from icing conditions into drier air. If they fail to do so, the system could overheat within minutes and damage the engine pod.

That defect has delayed certification of the MAX 7 and 10 models.

Boeing originally asked the FAA for an exemption to certify its MAX 7 without an engine anti-ice fix, arguing the dangerous condition was “extremely improbable” and that it could retrofit the new planes. There haven’t been any reported cases of aircraft damage due to overheating.

Boeing dropped its exemption request in January 2024 after a panel flew off an Alaska Airlines 737 MAX 9 midflight, reigniting scrutiny of the company’s manufacturing practices.

Now, Boeing is “right in the final stages” of certifying its engine anti-ice solution with the FAA, according to Chris Payne, Boeing’s vice president and program manager for 737 development programs.

The solution includes an “inlet turbulator,” a series of washers and fasteners that go through the engine inlet in a circumferential row. As air comes into the engine over the inlet, it hits those washers and swirls with colder air, dropping the temperature “at the critical point” by 200 degrees Fahrenheit, Payne said.

The engine anti-ice update includes a number of other changes, which Payne described as “localized things.”

Once certified, Boeing will incorporate the new engine anti-ice system first on its MAX 8 and 9 planes already in production.

If the FAA mandates a retrofit to existing planes, Boeing doesn’t have an estimate for how long that work could take or how much it would cost, a spokesperson said.

Certification updates

Boeing has completed all the required flight testing for its MAX 7 certification and has submitted 95% of the “deliverables” required by regulators, Payne said. It has completed 686 flight test hours, 441 total test flights and 349 ground test hours.

On the MAX 10, Boeing has completed 98% of its flight testing, including 2,060 flight test hours, 972 total test flights and 1,033 ground test hours, but it has further to go on its deliverables.

Boeing is still working to complete the final stage of its “development assurance review,” when the regulator checks that “you did everything you said you would do and needed to do,” Payne said, as well as its system safety analysis.

For the 777X family, Boeing is planning to first certify the 777-9 passenger variant. It is halfway through certification flight testing, according to Terry Beezhold, the 777-9 vice president and general manager.

It is working through the fifth and final step of a series of ground inspections, conformity reviews and flight tests.

Then, it will turn to extended-range performance standards to ensure the plane can fly over oceans and other areas far from airports.

At the same time, it is working on pilot qualification testing and training as well as developing simulators.

“This airplane’s been around and put through its paces, and the airplane is performing very well. It’s very mature,” Beezhold said. “We’re very excited to finish this program. We’re on the path to do that this year.”

In the meantime, Boeing has been running 777-9 “fatigue testing,” where it puts the shell of a new plane into a large, complicated system of pulleys, actuators and counterweights meant to simulate wear and tear on the airframe and wings.

The apparatus, tucked away in a corner of Boeing’s Everett campus, holds the fuselage above the ground and groans and hisses as it mimics the cycles of pressurization and depressurization.

Boeing has run its 777-9 through 63,000 flight cycles, from simulated takeoff to landing, and will continue its fatigue testing until the plane has accumulated the equivalent of three lifetimes, or more than 100,000 flight cycles.

The testing is meant to ensure the plane’s structure will continue to meet design and regulatory standards as it racks up flight hours and helps Boeing identify any areas of concern long before they pose a safety risk.

This story includes information from The Seattle Times archives.

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