Boeing has set up four sites to modify non-compliant vertical fin attachment fittings on undelivered 737 MAXs, including one in the space formerly used for 747 production.

In addition to space in Boeing’s famous 40-21 building and widebody production facility in Everett, Washington, 737 re-work is being done at three other familiar Washington State locations: its Renton, Washington, narrowbody factory; Boeing Field; and at Moses Lake, sources with knowledge of the process confirmed to Aviation Week.

Boeing has to modify about 170 undelivered aircraft to correct non-conforming attachment fittings. Supplier Spirit AeroSystems discovered the problem, which affects some aircraft built as far back as 2019, in April. Two of eight attachment fittings per aircraft do not conform to Boeing’s requirements and must be replaced on undelivered aircraft. In-service aircraft are expected to require inspections and, if needed, replacements of fittings that show damage.

The Everett modification space, freed up as part of 747 production’s wind-down is slated to see at least 11 737 MAXs, Aero Analysis Parters reported. Expected repair time per completed aircraft is about 15 days, the report added. Aero Analysis was first to report the Everett re-work facility.

Boeing has not detailed repair times, but the two-week duration for completed aircraft aligns with what CEO Dave Calhoun said on a recent earnings call. 

“We are defining the scope of that work [and it is] measured in a few weeks, not measured in months,” Calhoun said. “We’re confident in that.”

Boeing said it has not changed full-year delivery or production-ramp plans, however. 

Repairs to partially assembled aircraft or subassemblies at Spirit’s Wichita, Kansas, manufacturing facility will take less time—likely “days,” Boeing CFO Brian West said.

Spirit has said it expects to need two months to modify about 40 affected subassemblies in Kansas.

The repairs, required to ensure U.S. FAA airworthiness certificates needed for delivery, will result in lower 737 program monthly production and delivery totals for several months, Boeing said. Spirit’s output also will slow temporarily, the company said, but it still expects to meet its full-year target for 737 ship-set production.