Boeing is juggling yet more bad news regarding its bestselling series. Earlier this month, the Federal Aviation Administration (FAA) called for inspections on some models of three variants from within the Boeing 737 MAX family. The potential issue, sparked by reports of cracks, means hundreds of aircraft based across the US will require additional specific checks from next month.

After a tumultuous history with the 737 MAX, the move spells further regulatory involvement for Boeing over the series. Albeit, no outright groundings have been ordered. However, the mandated inspections mark another bout of unwelcome news for operators of such models. So what has the FAA flagged, and what will the impact look like for airlines?

Possible Cracks Around The 737 MAX’s Forward Galley Door

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The FAA first signaled its involvement in November of last year, after Boeing issued guidance about possible issues in December 2024. Citing “reports of cracks” in a structural component found on 737 MAX 8, MAX 9, and high-density MAX 8-200 aircraft, the regulator published a notice of proposed rulemaking (NPRM). This laid the groundwork for potential action ahead. Cut forward to August this year, and this arrived, with the NPRM being followed up by an airworthiness directive mandating repetitive checks on some planes.

This meant operators were to be legally required to carry out specific assessments on such models in the years ahead. Namely, carriers would have to inspect “the fuselage skin” on their aircraft “for existing repairs” and implement “applicable on-condition actions” relating to potential cracks. Such cracks could possibly be found on both the jets’ fuselage skin and the bear strap around the forward upper corner of the forward galley door cutout, according to the FAA’s airworthiness directive.

The call for inspections was precautionary, originally coming from Boeing before the FAA ultimately mandated the work for airlines from September 10. That said, where cracks might be found, the FAA struck a serious tone. “[These] may lead to the inability of the principal structural element to sustain limit loads and adversely affect the structural integrity of the airplane,” it wrote. All told, there was a threat there, and one that would have to be constantly ruled out on hundreds of 737 MAXs over their lifetimes.

Hundreds Of 737 MAXs Covered By Directive In US

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An estimated 471 models of the three 737 MAX variants would be affected by the airworthiness directive in the US, the FAA wrote in its notice. While a far cry from the more than 2,300 737 MAXs delivered as of this June, based on Boeing data, those picked out by the FAA were solely US-registered aircraft. Indeed, the European Union Aviation Safety Agency (EASA) also adopted the directive, meaning the number of jets covered globally would be higher.

Those ultimately set to be impacted included models from when the 737 MAX was first built to those delivered in early 2023, as reported by Aviation Week, with the final airframes in question falling under production line number 8711. That would cover a hefty number of jets given the 737 MAX’s commercial entry in 2017; therefore, the total globally is said to sit at over 1,400.

Mandated inspections also came at a cost. In the US, regulators set this at $85 per visual check of the planes’ exterior—a process said to take one hour. More detailed eddy-current inspections, which use electromagnetic induction to find defects, would then cost up to $340 each time, per the FAA. That meant a total bill of $40,035 and $160,140 per process, respectively, shared among airlines accountable for the 471 impacted models in the US, every time assessments were required. That is also before any potential issues were identified, meaning the actual cost could be higher if cracks were in fact found in the aforementioned bear strap and surrounding areas.

Bear Strap Issue Originally Found On Boeing 737 NG

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In any such case, the FAA guidance would leave operators having to obtain “instructions from Boeing for alternative inspections or for crack repair”. Reassuringly, though, this would not appear to be uncharted territory for the manufacturer. Rather, its initial sounding of the alarm bell stemmed from a similar issue discovered on older Boeing 737 Next Generation (NG) airframes in 2019.

As a result, the FAA issued an inspection plan and implemented a separate airworthiness directive. Again, this centered on the same type of bear strap structural reinforcement, with Boeing using a similar design and manufacturing process between the older and newer 737s.

Bear straps themselves are metal sheets used to reinforce areas like doorways and emergency exits on planes. In Boeing’s case, these components sit in the same area on both the older and newer 737s. Here, cracks have historically formed due to “stress concentration” at this door-cutout corner on earlier models, hence the fears that the same problem could emerge one day on the more recent 737 MAX fleet. Whether this actually happens, well, that is what Boeing sought out to prevent.

737 MAXs Likely Too Young To Show Bear Strap Cracking

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In reality, no such instances of bear strap or related fuselage cracking are said to have emerged on the 737 MAXs flagged by the FAA. Instead, both Boeing’s initial December 2024 alert and the subsequent regulatory involvement were preventative measures.

Where 737 NGs showed cracking, this followed about 15 to 20 years of service, or between 33,000 and 44,300 cycles. In contrast, the busiest 737 MAXs were approaching 10,000 cycles as of early August and had been in active service for roughly eight years, according to Aviation Week’s Tracked Aircraft Utilization tool.

Ultimately, that would mean the initial round of inspections on the newer models actually falling well into the future. Namely, at current utilization rates and with the FAA’s mandate requiring action before 30,000 cycles, these would only begin taking place in the early 2040s. Nonetheless, the episode will still be unwelcome for Boeing and its customers, given the checkered past of the 737 MAX program.

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Although not an immediate issue, any future problems relating to the 737 MAX program would be far from the first. The 737 MAX 8, the first in the family to enter service commercially, arrived in May 2017 with Lion Air subsidiary Malindo Air. The stretched 737 MAX 9 then followed with Lion Air almost a year later in March. Tragically, two crashes in quick succession followed.

Both involving MAX 8s, the incidents in Indonesia and Ethiopia saw 346 people killed between 2018 and 2019. America’s FAA and its peers around the world subsequently grounded all 737 MAXs for 21 months, after finding a flawed automated flight control system behind the crashes.

Core 737 MAX family specifications, from Boeing:

As it turned out, the two disasters were not to be the end of the story, with Boeing and the 737 MAX once again fetching unwanted headlines in early 2024. This time involving a 737-9, a door panel blow-out during an Alaska Airlines flight prompted the variant to be grounded for several weeks. Pilots landed safely in this case, but the fallout left Boeing once again under intense scrutiny.

Boeing Already Acting On Possible 737 MAX Issue

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For Boeing, the latest mishap adds another potential problem after several tough years for its 737 MAX program. The difference this time, however, is that the manufacturer has seemingly got ahead of the curve. No such cracking has yet been found on the fleet, and it might not be for years to come, with the inspection process instead aimed at catching anything before it is too late.

“Boeing identified and reported this issue and has been working with operators on it over the past six years,” a spokesperson told Simple Flying.

They added that checks were set to “provide multiple opportunities to identify and correct possible cracking before cracks exceed critical length”. Meanwhile, they said work was underway to prevent such cracking.