Southwest Airlines and Brazil’s Gol Linhas Aereas were among the companies which carried out checks after the US Federal Aviation Administration told airlines to urgently inspect older 737s, starting with those that have made at least 30,000 flights.
The regulator ordered about 165 US planes be checked within seven days when cracks were found in planes undergoing work in China.
A Southwest spokesman said crews inspected more than 200 aircraft and found signs of cracking on two, which will remain out of service until repairs have been done.
Minor aircraft cracks are not unusual, an industry source said, but are not normally expected to occur on the pickle fork until near the end of the plane’s lifespan, considered to be more than 90,000 take-off and landing cycles.
The planes are a version of the Boeing 737 called the NG or next generation. They were first delivered in 1997.
Boeing is replacing the NG with the 737 Max, but the Max remains grounded worldwide after two crashes killed 346 people, although it is unaffected by the cracking issues.
More than 1,700 planes must be checked before they fly another 1,000 times.
American, United and Delta said none of their Boeing 737s needed to be checked within seven days but they have some that will need inspections over the next few months.
Southwest said it had completed all inspections in compliance with the seven-day deadline and had reported the findings on its two planes affected to Boeing and the FAA.
“The aircraft will remain out of our schedule until the issues have been fully resolved,” the company said. “Safety is always our uncompromising priority, and our technical operations team is now focused on completing inspections of the remaining portion of the 737 NG fleet covered by the Airworthiness Directive.”