QANTAS has grounded a quarter of its Boeing 737-400 fleet because of discrepancies in maintenance paperwork.

The airline said it had grounded the six jets to check records relating to modification work at one of its Australian facilities. The executive general manager of Qantas Engineering, David Cox, said there were no safety implications.

It was to "ensure all our records are 100 per cent accurate and we have advised the Civil Aviation Safety Authority", he said.

CASA says it will look into the grounding as part of its investigation into the airline's maintenance procedures, launched last week, after a series of recent faults, including the explosion of an oxygen tank on a 747-400 last month that blew a large hole in the plane's fuselage.

"We want to make sure that all maintenance documentation is all OK," a CASA spokesman said.

Last week Qantas shelved plans to send two 737s to Malaysia for maintenance after the first plane sent there two months ago came back with 95 defects.