At least one of South Korea's KF-16 fighter jets has been found to have a serious engine problem similar to that of a same-model jet that crashed here last month, a senior Air Force official said Thursday.

He added that dozens of other KF-16 fighter jets have been also grounded for checkups on possible engine hitches, which the Air Force ascribed to engineers' negligence of duty or even corruption.

But he refused to reveal the exact number of planes grounded, only saying 60 percent of about 130 KF-16 jets in the country are in normal operation.

"Some remain grounded because of the need for closer technical checkups in the wake of a recent KF-16 jet crash, while others are not in service for routine maintenance," the official said, asking not to be named.

Safety concerns about South Korea's fleet of KF-16 jets have been rekindled since a jet went down in the West Sea on Feb. 13.

Its engine failure was caused by poor maintenance, investigators said. Each KF-16 jet is priced at around 40 billion won (US$42 million).

The U.S. engine maker Pratt & Whitney, which supplied the KF-16's engines, advised the Air Force to replace a flawed part of the doomed jet's engine or risk an accident, but mechanics ignored it, according to the Air Force's in-house probe.

The Air Force immediately conducted a wider audit on its plane maintenance and logistical supply system.

Announcing his resignation on Wednesday, Air Force Chief of Staff Kim Sung-il said he was "shocked" by what the audit revealed.

"Structural flaws in the Air Force's logistical supply system have been confirmed, and I was shocked by the fact that a number of officials will face punishment," he said in a statement.

The four-star general said he decided to step down to take full responsibility for the problem on behalf of the engineers.

President Roh Moo-hyun was quick to accept Kim's resignation.

The Defense Ministry and state auditors are separately looking into allegations that a large amount of the budget for fighter jet maintenance have been embezzled, and maintenance-related records have been fabricated.

"Through our investigation on some sampled engines, we found that at least one more KF-16 fighter jet has the same engine problem as the aircraft that crashed last month," the Air Force official said. "But the jet had continued flights until recently, as engineers fabricated their servicing records."

He added that the Air Force has removed a total of 60 engine turbines with the same product code as that of the doomed jet for scrutiny.

"We completed an inspection of 10 engine turbines, and found that one of them is flawed," he said. "We plan to disassemble the remaining 50 engine turbines for precise checkups."

Defense sources said last month's jet crash appears to be just the tip of the iceberg, given the chronic corruption in the Air Force's jet maintenance sector.

Seoul, March 22 (Yonhap News)