Boeing Co said Thursday that airlines had inspected 810 of the company’s 737 NG jets around the world, and found 38 structural cracks requiring repair and replacement.

The planes will be grounded until the repairs are made, Boeing and airline officials said. Nearly five per cent of inspections have found cracks in a “pickle fork” — a part that attaches the plane’s fuselage, or body, to the wing structure and manages forces.

The 737 NG is the third-generation 737 and the version before the now-grounded 737 Max, which is not impacted by the cracking issue.

On Wednesday, Southwest Airlines Co and Brazil’s Gol Linhas Aereas grounded at least 13 of the 737 NG airplanes after U.S. regulators ordered urgent inspections. The U.S. Federal Aviation Administration (FAA) last week told U.S aircraft operators to inspect 165 older 737 NGs for structural cracks.

American Airlines and United Airlines said earlier this week they have not seen any cracks in their airplanes.

Raymond James analyst Savanthi Syth wrote in a research note Thursday that the findings from the 737 NG inspections could “potentially take up to four per cent of capacity off-line” between mid-October and mid-December.”

Planes with cracks “may need to be taken out of the fleet for up to 60 days for maintenance,” Syth said.

The FAA last week said inspections would look for “cracking of the left and right hand side outboard chords of frame fittings and failsafe straps.”

It said the cracking “could adversely affect the structural integrity of the airplane and result in loss of control of the airplane.”

Aircraft with more than 30,000 cycles must be inspected within seven days, while planes between 22,600 and 29,999 cycles must be inspected within 1,000 cycles, which typically correspond to the number of flights. In total, 1,911 U.S. 737 NGs are covered by the FAA directive.