Second life for CF34 fan blades

OEM repair procedure GE Engine SB 72-0148
Further 18,000 cycles of life

The fan blades on the CF34-3 jet engine have to undergo eddy current inspection and flourescent penetrant inspection after 18,000 cycles and then after every further 3,000 cycles. Lufthansa Technik has introduced an OEM repair procedure, GE Engine SB 72-0148, that enables it to give the components a further 18,000 cycles of life – avoiding the need for more frequent inspections. 

Unique repair competence in Europe

When the approval from manufacturer General Electric (GE) arrived in Hamburg the responsible product engineer was not the only one who felt pleased. This letter from Cincinnati means that Lufthansa Technik is now in possession of a competence in the repair of fan blades for the GE CF 34-3 engine that is unique in Europe. This engine, which is employed on the Bombardier regional jets amongst others, has a limit of 18,000 cycles on the fan blades. At this point and after every further 3,000 cycles the fan blades have to undergo an eddy current inspection (ECI) and flourescent penetrant inspection (FPI) – a time-consuming operation that is difficult to reconcile with routine flying operations. 

Eliminating the short inspection interval

But with a one-off repair to the fan blades it is now possible to eliminate the short inspection interval. Under the procedure now licensed by the manufacturer, the blade root tangs are fitted with bushings. The process of fan blade bushing installation starts with reaming the tangs to achieve a certain diameter. Prefabricated bushings are then inserted and fixed using a specially developed procedure known as "cold expansion". This entails drawing a precisely dimensioned mandrel through the bushings with hydraulic support. These change their shape so that they sit really firmly in the tangs. To obtain the approval, Lufthansa Technik had to demonstrate this procedure. To complete the process, the bushings are finish machined, following which the fan blades are fit for a further 18,000 cycles. 

Supplementing an extensive CF34 portfolio

With the new process, Lufthansa Technik's EPAR business unit is extending its competence in CF34-3/-8 fan blade repairs to incorporate an important new element as a supplement to all open book repairs such as blending, peening and hard face coating. On the basis of the success of the repair, Lufthansa Technik now plans to introduce this procedure in the near future for the CF34-8 type as well.