Qantas has hit back at its engineers' union's "alarmist" call to ground its entire fleet of Boeing 737-800s, after one of them was found to contain structural cracks.

Qantas has hit back at its engineers' union's "alarmist" call to ground its entire fleet of Boeing 737-800s, after one of them was found to contain structural cracks.

Calls by the Australian Licensed Engineers Association followed Qantas's inspection of 33 older 737NGs for cracks, in line with a directive from the US Federal Aviation Administration.

At the heart of inspections is a structure known as a "pickle fork", which connects the wing to the fuselage of 737-800s. Cracking of the structure could result in failure, affecting the integrity of the aircraft and potentially resulting in loss of control.

The Oneworld carrier says it "rejects the alarmist claims" for grounding made by the engineers' association which, it argues, are "irresponsible and completely inconsistent with advice from regulators and the manufacturer".

The FAA order required US airlines to inspect over 1,900 737NGs all of which have accumulated more than 30,000 flight cycles. Aircraft that have logged 22,600-30,000 cycles are to be inspected within the next 1,000 cycles, which Qantas says equates to about seven months of flying.

Qantas says none of its 75 737-800s has flown more than 30,000 cycles. However, 33 of them will have to be inspected within the next seven months.

Inspections so far indicate one 737-800 had sustained cracks. While Qantas did not specify the aircraft's registration, it states that jet had flown about 27,000 cycles.

Qantas says its checks on the 33 older 737NGs are slated to be completed by 1 November, ahead of schedule. "Qantas would never operate an aircraft unless it was completely safe to do so," the airline adds.

Virgin Australia, another Australian carrier that operates the 737NG, states that 19 aircraft were inspected, and none was found to contain cracks. Cirium fleets data indicates that Virgin Australia operates 62 737-800s and two 737-700s.

Earlier this month, civil aviation authorities in Indonesia grounded three older 737NGs after inspections revealed similar structural cracks.