Dallas (dpa) - The US airline Southwest Airlines has due to cracks on important components two Boeing 737 NG jets from circulation. The problems had been discovered in an inspection ordered by the US aviation authority FAA, the airline said.

However, the vast majority of the fleet examined was in order. The two machines would not be used again until the problems are completely resolved. "Safety and quality are our top priorities," the company emphasized.

The FAA had instructed some operators of Boeing's 737 NG last Wednesday to inspect the machines for cracks within seven days. The manufacturer had discovered the problem itself and informed the authority about it. The risk of cracks exists in so-called pickle forks, which are important components for attaching the wings to the fuselage. Under heavy load they can obviously wear out faster than expected.

Boeing affirmed in an opinion to actively support its customers in the investigations of the 737 NG. All the operators concerned were given detailed instructions and Boeing also participated in necessary repairs.

The 737 NG is the predecessor of the misfortune 737 Max, which was in mid-March after two crashes with a total of 346 dead almost worldwide with start bans.

Southwest Airlines is not the only airline that had to inspect Boeing's 737 NG for cracks at the FAA's direction. According to a Bloomberg report, many more problems were identified. Based on preliminary findings from Boeing, five percent of the total of 493 older 737-NG machines under investigation had cracks. These jets are now temporarily unable to take off. The Financial Intelligence Service relies on an anonymous source, which has the information from a conference call between representatives of Boeing and airlines.

The aircraft manufacturer sets up a repair station in Victorville, California, the report said. Boeing expects to need about two to three weeks per aircraft to fix the problems. The US group did not comment on this at first. One thing is for sure: Boeing already has enough stress with the crisis flyers of the 737 Max series. The large US carrier American Airlines expects, according to data from Wednesday this year, no longer with a restart of the bad luck jets.

The company said it would take the aircraft out of the flight schedule by 16 January. Boeing's bestseller thus fails in the marked by strong travel income Christmas time. Previously, American 737 Max flights had been canceled until December 3. Given the ongoing difficulties in the intended reclassification of the machines, the step comes as little surprise. Boeing is under pressure to fix software issues that are considered a major cause of the two crashes.