London (CNN Business) Ryanair is the latest major Boeing customer to find cracks in some of its 737s.

The Irish airline said in a statement Wednesday that inspections ordered by US regulators had turned up problems with a small number of its oldest 737s, which are now being repaired by Boeing.

The US Federal Aviation Administration ordered inspections of Boeing 737 NG, or Next Generation, aircraft in September after the company said structural cracks had been found on heavily used planes.

The cracks were found on what is known as the "pickle fork," which helps attach the wings to the aircraft.

Boeing BA The cracking issue is the latest blow to. All 737 Max jets, a newer version of the aircraft, have been grounded since March following two fatal crashes that killed 346 crew and passengers.

Read More