London - Ryanair has grounded three planes after cracks were found between the wings and fuselage.
The budget carrier had been ordered to carry out checks on its older Boeing 737-800s after defects were found in identical jets operated by other airlines.
The problem affects the "pickle fork" section of the plane, which attaches the wing to the main body. Aviation regulators ordered urgent inspections after the issue was spotted on jets owned by Australian airline Qantas and the US carrier South West.
Ryanair said last week that it did not expect the issue to have an impact. But on Wednesday it was forced to confirm its planes had been affected after copies of repair logs were leaked to The Guardian.
The airline described as "rubbish" a suggestion it had quietly withdrawn the planes from service without telling members of the public. According to flight logs, two of the jets were ferried to California for repairs. The other is in a hangar at Stansted.
Last month all operators of Boeing 737s were given seven days to check their fleets for signs of cracking. The issue mainly affects older versions of the plane, which have carried out more than 30 000 take-off and landing cycles.
Boeing has completed checks on all such aircraft and found faults with fewer than five percent.
A spokesperson for Ryanair said on Wednesday: "This morning’s report on the 'pickle fork' issue in The Guardian newspaper is rubbish.
"Ryanair has already inspected over 70 of its oldest aircraft in full compliance with the Airworthiness Directive, and our rate of findings is less than the industry wide five percent confirmed by Boeing.
"Boeing are carrying out these repairs on behalf of Ryanair. We are confident the tiny number of pickle fork cracks, if any, will not affect either Ryanair’s fleet, its flights, or its schedules."
Boeing is already under intense pressure over its handling of two deadly crashes involving its new 737 Max aircraft. Chief executive Dennis Muilenburg was last week accused of deliberately concealing problems with the planes.