Qantas says it has grounded three aircraft with hairline cracks in the "pickle fork" structure after completing inspections of 33 of Boeing 737NG jets. The precautionary checks of the structure that helps connect the wings to the fuselage were done as part of a global Airworthiness Directive (AD) by the US Federal Aviation Administration after similar cracks were found in jets in China. READ: Qantas to launch domestic fleet renewal process in 2020. The FAA said at the time the condition “could adversely affect the structural integrity of the airplane and result in loss of control of the airplane”  and ordered jets with the cracks to be grounded until they could be fixed. A report today by news agency AFP indicates about 50 jets have been grounded worldwide since the FAA issued the directive on October 2 with other affected carrier's including Southwest Airlines and Brazil's Gol. The aircraft inspected by Qantas were due to be inspected within 1000 take-off and landing cycles but the Australian carrier proactively brought forward the inspections by up to seven months. Rival Virgin Australia has also completed checks of its B737s affected by the AD. The aircraft with cracks have been removed from service pending repairs and had all completed around 27,000 cycles. Qantas said any aircraft with more than 22,600 cycles was inspected, in line with advice from regulators. It added it would minimize any customer impact from having these aircraft temporarily out of service while it worked with the Civil Aviation Safety Authority and Boeing to resolve the issue. Describing the repair work as complex, it said it expected all three aircraft to return to service before the end of the year. Qantas said it would continue to monitor aircraft that are in the scope of the AD.  Inspections fall due every 3500 cycles. “As people would expect with Qantas, we’ve gone above what was required to check our aircraft well ahead of schedule,'' Qantas Domestic chief executive Andrew David said. "We would never fly an aircraft that wasn’t safe. Even where these hairline cracks are present they’re not an immediate risk, which is clear from the fact the checks were not required for at least seven months." The discovery of the cracks prompted the Australian Licenced Engineers Association to call for the immediate grounding of all Qantas Boeing 737NGs until checks were completed and the aircraft were deemed safe. But David branded the comments as irresponsible and said they completely misrepresented the facts. "Those comments were especially disappointing given the fantastic job our engineers have done to inspect these aircraft well ahead of schedule, and the priority they give to safety every day of the week.” A CASA spokesman told AirlineRatings on Wednesday that the authority was satisfied by the airlines' response to FAA directive. Boeing says the cracked frame of fail-safe strap must be removed and replaced. The manufacturer said it was engaged with its 737NG customers globally on the inspections and was “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”. “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,” it said. The problem does not affect the Boeing 737 MAX, which is grounded due to other issues.