Show caption The 737 Max was taken out of service in March after the second fatal crash in four months. Photograph: Lindsey Wasson/Reuters Boeing Further safety issue found in grounded Boeing 737 Max planes Airlines told to check aircraft as affected components may be at risk of premature failure Gwyn Topham Transport correspondent @GwynTopham Mon 3 Jun 2019 17.01 BST Share on Facebook

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Safety regulators in the US have identified a further problem in Boeing’s grounded 737 Max model and the generation of planes that preceded it.

The Federal Aviation Administration has told airlines to check more than 300 737 aircraft, including 179 of the Max model, for improperly manufactured parts.

The affected components – part of the wing – help provide lift during takeoff and landing, and “may be susceptible to premature failure or cracks resulting from the improper manufacturing process”, the FAA said on Sunday.

The 737 Max, Boeing’s top-selling passenger jet, was taken out of service in March after the second fatal crash in four months. A total of 346 people died in the Ethiopian Airlines and Lion Air disasters.

The manufacturer said it had not been told of any issues during flying regarding the potentially faulty parts. It said there were 20 737 Max airplanes that were likely to have the defective parts, and that airlines would check an additional 159 planes. Another 133 of the 737 NG model, a predecessor to the Max, will also be checked.

The FAA said a complete failure of the part, called a leading-edge slat track, would not cause a crash, but could cause aircraft damage in flight. Airlines operating the affected NG planes need to remove faulty parts within 10 days, but can continue to operate them in the meantime.

However, the wider worries around the 737 Max led to a $1bn (£790m) order being put on hold on Monday, as the Azerbaijan airline AZAL postponed an order for 10 planes.

Boeing has yet to finalise a software upgrade, which it hopes will convince regulators that it is safe for the plane to return to the skies. Although investigations continue, a controversial automated anti-stall system, MCAS, has been implicated in both crashes.

Last week, the head of the global airline trade body, IATA, said it would be at least August before the all clear was given, with regulators outside the US having indicated that they will also expect to give separate clearance rather than accept the FAA ruling.