A mass inspection of older Boeing 737 NGs worldwide has found 36 with cracked wing supports, resulting in their grounding pending repairs, the aerospace giant said Wednesday.

That represented about 5% of the 686 planes inspected for cracks following an order issued last week by the Federal Aviation Administration.

Some airlines were hit harder than others. Southwest Airlines had two planes that will have to be taken out of service pending repairs and Brazilian carrier GOL had 11, according to multiple news reports.

The cracks, discovered when several planes were being converted from passenger to cargo use, represented another blow to Boeing, still reeling from the crashes of two of the latest version of the venerable 737, the Max.

"Boeing regrets the impact this issue is having on GOL, as well as our 737 NG customers worldwide," the company said in a statement. "We are actively working with our customers with inspection findings to procure parts, develop repair and replace plans, and provide all the technical support needed to safely return every impacted airplane to service as soon as possible."

More:Boeing faces new 737 issue: Cracks in wing supports on popular NG version

The NG, for Next Generation, was the previous version of the 737 that has become one of the world's most popular jetliners. Southwest alone has about 700 NGs in its fleet. American has 304 and Delta has 200.

The inspection order covered only some of the most heavily flown 737 NGs. The cracks were found in a component called the pickle fork, which help attach the wings to the fuselage. The FAA said the cracks could "adversely affect the structural integrity of the airplane and result in loss of control of the airplane" if not addressed.

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The 737 NG crack issue came as Boeing continues to try to revamp and test the flight control system in the 737 Max, grounded after the crashes of Lion Air jet a year ago and an Ethiopian Airlines flight in March.

The crashes occurred after pilots on both jets wrestled with the automated system, which kept pushing the plane's nose down as they tried to keep it aloft.

A total of 346 people died in the two crashes.