The grounding is the latest safety concern for United States-based planemaker, as it tries to deal with the fallout from crashes of two 737 MAX planes – which are newer than the NG model – that killed 346 people and highlighted problems with the MAX’s flight handling software.
The US Federal Aviation Authority (FAA) earlier this month ordered checks of Boeing 737 NG planes that had taken off and landed more than 30,000 times.
That came after the company reported that “pickle forks”, which help connect the wing to the body, could be prone to cracking.
Qantas said on Thursday it found the fault in a more lightly used aircraft, one that had recorded fewer than 27,000 flights. The Reuters news agency quoted a Qantas spokesman as saying that none of its planes had yet reached 30,000 flights.
“This aircraft has been removed from service for repair,” Qantas said in a statement, adding it has sped up its inspections of 32 other 737 NG planes to be completed by Friday.
The announcement by Qantas raised fears the cracking issue could affect newer planes than previously thought, leading to calls for the airline to ground its entire 737 fleet.
“These aircraft should be kept safe on the ground until urgent inspections are completed,” Steve Purvinas, the federal secretary of the Australian Licensed Aircraft Engineers Association, said in a statement.
However, Qantas described the call to ground its 737 fleet as “completely irresponsible”.
“We would never operate an aircraft unless it was completely safe to do so,” Qantas head of engineering Chris Snook said.
“Even when a crack is present, it does not immediately compromise the safety of the aircraft.”
The FAA initially said Boeing notified the agency of the problem after encountering the issue on a plane in China and that subsequent inspections showed other planes also had cracks.
Repairing the cracks requires grounding the aircraft, with remedial work costing an estimated $275,000 per aircraft, according to aviation consultancy IBA.
In a filing with the US Securities and Exchange Commission last week, Boeing said all 737 NGs with more than 30,000 flight cycles and about one-third of planes with over 22,600 flight cycles had been inspected for pickle fork cracks.
The manufacturer said additional assessments were under way to determine the cause and potential implications for planes with fewer than 22,600 cycles.
Reuters reported on Wednesday that US-based Southwest Airlines is also stepping up checks on its 737 NGs for cracks.
The NG is a precursor plane to the Boeing 737 MAX, which has been grounded since mid-March following the two deadly crashes in Indonesia and Ethiopia.
Boeing chief executive Dennis Muilenburg faced another round of tough questions on Wednesday from US legislators who accused the company of a “lack of candour” over the crashes.