CFM INTERNATIONAL (CFMI) is redesigning the fan-blade-retention device on the CFM56-7B2 for the third time in an attempt to complete certification testing for the engine type for the new-generation Boeing 737.

The new test will take place "around the end of September", says CFMI, which realises that this could be its last chance to complete certification in time to prevent the tight 737 timetable from slipping behind schedule. The first aircraft is due to be rolled out on 8 December and be flown in early February 1997. CFMI says that it is confident that the new test will be "third time lucky", and says that the certification schedule is not threatened at present.

The CFM56-7 is the first of the family to be fitted with wide-chord fan-blades, which are around 35% heavier than those of the -3 version, which powers all current-generation 737s.

Testing of the Snecma-designed unit and associated changes in the engine have caused problems. These snags cropped up when the engine failed its blade-off test because the retention device on the blade roots was not stiff enough.

The retainers were strengthened for the retest, which took place in late August. The test again failed, this time because the retainers were too strong. CFMI engineers say that the problem will be solved by, "re-distributing the energy between the fan and the retainer".

The engine is due to be certificated in late October.

Source: Flight International