Ryanair and more than 100 other airlines have been ordered to conduct emergency inspections on some of their Boeing 737 aircraft following last week's fire on a China Airlines aircraft.
Boeing wrote to Ryanair and other Boeing users on Saturday setting out the necessary inspection regime for all so-called "next-generation" 737s manufactured after 1998.
There are more than 2,300 such aircraft around the world.
The fire on the China Airlines Boeing 737-800 last Monday week was thought to have been caused by a loose bolt that punctured the fuel tank.
The fire began after the plane landed in Okinawa, Japan, and all 165 passengers and crew were safely evacuated.
The US carrier South West Airlines is the largest single operator of 737 next-generation aircraft, Jim Proulx, Boeing's communications director, said.
"But Ryanair is easily in the top five," he added.
A spokeswoman for Ryanair said the company welcomed the directive. Inspections on its fleet of Boeing 737s were well under way, and were not causing disruption.
"Nothing has been discovered thus far arising from the inspections. Ryanair expects to complete the inspections well before the required 24-day deadline."
The Boeing instructions were followed in the US by a directive from the Federal Aviation Administration to operators such as South West Airlines, Delta and American Airlines.
Mr Proulx said he expected that the European Aviation Safety Agency would issue a similar directive to airlines operating in Europe.
Japan's transport ministry said all Japanese operators had conducted similar checks.
