The Land, Infrastructure and Transport Ministry announced Tuesday it will tighten its inspections of Skymark Airlines after the carrier reported it had been operating a plane for about nine months past a repair deadline.

Transport minister Kazuo Kitagawa told a news conference that Skymark's negligence in not repairing the Boeing 767-300, reported to the ministry Friday, was extremely regrettable and the ministry will send inspectors to check its maintenance facilities.

"An airline must not sacrifice safety to pursue efficiency or reduce costs," Kitagawa said, adding that safety was the most important mission for any operator of mass transportation.

The minister said Skymark appears to be using less maintenance staff per plane than big operators Japan Airlines and All Nippon Airways.

Ministry officials summoned senior Skymark officials later in the day to give them a warning document on its repair infractions.

The carrier was also told to check for any other cases of missed repairs and to file a report on how it plans to prevent a recurrence by March 28.

The forgotten repairs were to a Boeing 767-300 that had a fuselage dent 60 mm long, 15 mm wide and 1 mm deep under the front starboard-side door. The damage was found during maintenance at a Taiwan airport in June 2004 when it was being operated by an unnamed Brunei airline, according to the ministry.

A Taiwan maintenance company put a plate over the dent to repair it under instructions from U.S. maker Boeing Co., which said more extensive repairs would be needed in one year.

The plane was sold to Skymark in November that year and put back into service the following month.

At the time of delivery, the Brunei airline gave Skymark a document saying further repairs were necessary, but Skymark claimed it was not aware of the instructions.

Skymark notified the transport ministry Friday of the missed deadline after an employee discovered it the previous night.

The airline said in a statement issued Tuesday that it took the plane in question out of operation and had the repairs done immediately after it realized the plane had been operated for about nine months past the deadline. Skymark had Japan Airlines do the repair work, which was completed Monday.

Skymark "deeply apologizes for causing concern among customers," the statement says.

The B767-300 went back into operation Tuesday morning with a flight from Tokyo's Haneda airport to Tokushima, Skymark said.

In its statement, Skymark acknowledged it has a document giving the deadline for repairs but blamed its failure to meet it on poor communication between it and the Taiwanese maintenance firm.