Between the adjacent fan blades of the CFM56-7B engine, 24 Fan Blade Platforms, made of forged aluminum, are installed to provide an aerodynamic surface.
Recently, CFMI has introduced a new Fan Blade Platform design (p/n 340-001-814-0). The Fan Blade Platform design changes include:
-No life limitation
-New geometry with swaged bushings
-New material, aluminum 7449
-Weight decrease (-36 grams)
-Bowl seal implementation on both sides (lip seal removed)
-No elastomer strips needed for weight balancing
The new Fan Blade Platform can be identified by a grey stripe on the aft edge of the platform surface (fwd looking aft).
The new design platforms weigh 36 gram less than the current design. Because of this mass difference, a single replacement of a current design platform (p/n 340-001-804-0, 340-001-805-0, 30-001-806-0, 340-001-809-0 of 340-001-810-0 ) by a new design (p/n 340-001-814-0) will generate an unbalance equal to a momentweigth of approx 925 cm/g, which will result in engine fan vibration. Therefore, the current and new design platforms are only interchangeable as a complete set. However, to avoid any operational desruption due to lack of spares, the current design platforms can be replaced by the new design platforms only when installed in pairs (two platforms with the same reference, 180 ‘degrees apart).
Engine vibration levels must be within limits during the test run that has to be performed after this action. The new design Fan Blade Platforms are only one way interchangeable and can not be replaced by the current design platform.
This limited interchangeability information and the accomplishment instruction for Fan Blade Platform installation in pairs can be found in CFMI (CFM56-7B) SB 72-0353.
See pictures below for examples and differences between old and new design platforms.