Qantas has labelled calls for its entire fleet of Boeing 737-800s to be grounded by its engineers’ union as “completely irresponsible”.

The kangaroo carrier is currently undertaking an immediate inspection of 33 of its Boeing 737 Next Generation airplanes that have operated on more than 22,600 flights, after discovering a structural crack on the “pickle forks” of one of its aircraft during a scheduled maintenance check.

But the Australian Licensed Aircraft Engineers Association (ALAEA) on Thursday called on Qantas to immediately ground all 75 Boeing 737-800 aircraft, after an alleged second aircraft was found with a structural crack.

“These aircraft should be kept safe on the ground until urgent inspections are completed and advice in relation to the ongoing nature of the wing cracks is confirmed by Boeing and the US Federal Airworthiness Authority,” ALAEA said in a statement.

Boeing, the manufacturer of the aircraft, has notified all of its customers of the issue, as it investigates the root cause of structural cracks on the pickle forks of certain 737 NG model jets, which attach the wing of the jet to the body.

The issue reportedly does not immediately compromise the safety of aircraft.

“Boeing is actively working with customers that have airplanes in their fleets with inspection findings to develop a repair plan, and to provide parts and technical support as necessary,” a spokesperson for the aircraft manufacturer told Travel Weekly.

Qantas has called the allegations and comments made by the association “completely irresponsible”.

“We would never operate an aircraft unless it was completely safe to do so. Even when a crack is present, it does not immediately compromise the safety of the aircraft,” Qantas’ head of engineering, Chris Snook, said in a statement.

“Safety regulators in Australia and the United States require the checks on our 737s to be completed over the next seven months. Our checks are well advanced and will be finished by tomorrow – months ahead of schedule.

“These inspections are being conducted by airlines globally. As other airlines have done when they have found cracks, Qantas will remove aircraft from service so they can be repaired.”

The Federal Aviation Administration (FAA) has issued a mandate for all 737 NG models – which includes the 737-800 – to be inspected prior to the accumulation of 30,000 total flight cycles.

Qantas would not confirm whether a structural crack in a second aircraft had been discovered when asked by Travel Weekly, but said it will provide a further update once the checks are complete.

“Qantas has been liaising with Boeing and CASA on an issue affecting some of the global fleet of 737s,” the airline said.

“The advice requires immediate inspection of aircraft that have completed more than 30,000 takeoffs and landings (or, cycles). Aircraft with more than 22,600 cycles require inspection within the next 1000 cycles which, in Qantas’ case, is about seven months of flying.

“None of Qantas’ 737s have reached the 30,000 cycle mark. However, we will have inspected 33 aircraft with more than 22,600 cycles by the end of this week rather than the seven months required.”

A spokesperson from Boeing told Travel Weekly the issue does not affect any 737 MAX airplanes or the P-8.

“Boeing regrets the impact this issue is having on our 737NG customers worldwide and we are working around the clock to provide the support needed to return all airplanes to service as soon as possible,” the spokesperson said.