Boeing has warned operators of its 737 family of aircraft of a potential fault with the planes’ wings, including on the 737 Max that has been grounded since March following two crashes.

The aircraft manufacturer is advising airlines to inspect the slat tracks on all 737s after it identified more than 300 planes likely to have faulty parts.

The track guides slats located on the leading edge of the aircraft’s wings, which helps reduce drag on take-off and landing.

Boeing says affected parts may be susceptible to premature fault or cracks resulting from an “improper manufacturing process” carried out by one of Boeing’s suppliers, according to the US Federal Aviation Administration (FAA).

Though it is unlikely that the fault could cause an aircraft to crash, the FAA says a parts failure could cause damage to the plane in flight.

Operators are being advised to check all 737 models, including the 737NG and 737 Max versions, before returning them to service, though Boeing added that it has not identified any in-service issued.

The company is staging replacement parts at customers’ bases in an effort to reduce aircraft downtime, with the work expected to take one or two days. Operators of affected planes are required by the FAA to carry out this work within ten days.

In a statement, Kevin McAllister, president and CEO of Boeing Commercial Airplanes, said: “We are committed to supporting our customers in every way possible as they identify and replace these potentially non-conforming tracks.”

The news comes as Boeing waits to hear from regulators around the world on whether the 737 Max will be able to return to service after the company completed a software update for the aircraft following two fatal crashes.

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