Japan Airlines Corp. officials said Friday they know what caused the engine parts of 596 Japan Air System Co. flights to crack earlier this year: excessive brazing during maintenance.
The flights were grounded following the discovery of the cracks.
The U.S. manufacturer of the engine, Pratt & Whitney Co., found that brazing was the problem, they said. JAS and Japan Airlines Co. completed their merger under the holding company of JAL in April.
JAL said it will replace by the end of the year all seven engines that were brazed and are still in use. No cracks have been found on any of the seven engines.
Nineteen other brazed engines have already been replaced, company officials said.
JAS domestic flights were disrupted after engine problems were reported in MD-81 and MD-87 jetliners on Jan. 19. An emergency inspection found cracks on the stator blades in 21 engines on 18 jets of the same models. The stator blade controls the flow of air compressed by the rotor.
Brazing is often used to fill tiny gaps in stator blades. But Pratt & Whitney found that this practice actually weakens the strength of the blade.
The engines of the MD-81s and MD-87s had been brazed at a Pratt & Whitney maintenance plant in Singapore, JAL said.
A total of 40,000 passengers were affected by the cancellations.