A full blade-out test was successfully completed on CFM International's CFM56-7B turbofan at Villaroche, France, on 2 December, just six days before the unveiling of the first of the next-generation Boeing 737 series for which the engine is designed.

The engine was due originally to be certificated in late October pending the completion of the blade-out test, originally due in late September.

The test was the final hurdle to be overcome before certification, which is now expected before the end of the month. CFMI was required to re-run the test to check the blade-retaining device, which had to be re-designed following earlier failures. CFMI elected to perform the test on a full engine rather than on a test rig, to avoid any further delays to certification. Although far more expensive to run, the full engine test provided instant data to the certification authorities.

"If we had done it on a rig then we'd have had to show correlation between the rig data and the real thing. We did not want to do that because we want to be certificated before the end of the year," says the company. "If it had not contained blades, then we would have had to re-validate the containment system," the company says.

The engine was run up to around full power at 118kN (26,400lb) before an explosive charge was detonated at the base of one of the blades. "We got some minor damage to the leading edge of other blades, but the test was successful," says CFMI.

The new blade-retaining design strengthened the forward retainer, making it ten times stronger than the original. In the previous design, all the loads were taken by the aft retainer and, under the new configuration, loads will be shared equally by the front and aft devices. In the first attempt, CFMI discovered that the retainers were not strong enough. The redesign led to failure on a second test because the retainers were too stiff and distributed destructive energy levels to the other blades.

Source: Flight International