Aircraft

General Electric will sell, at a heavy discount, CF34-3B1 engine fan blades to Bombardier CRJ operators affected by a service bulletin calling for replacements to be installed over a two-year period.

The engine manufacturer has identified about 13,000 fan blades from CF34-3B1 engines that power CRJ200 aircraft as being defective. Rough estimates show the blades are present on about 1,500 CF34-3B1 engines.

"It's a shared expense," says a GE spokesman. "It takes two hours to replace the blades. When you go in for a shop visit, they can do a full inspection of the blade."

The US National Transportation Safety Board issued recommendations to the Federal Aviation Administration, citing a safety concern raised by two engine failures on CF34-powered CRJ200s. In both instances - a 27 July 2006 engine failure on an Air Nostrum CRJ shortly after take-off from Barcelona, Spain, and a 24 May 2007 engine failure on an Atlantic Southeast (ASA) airlines CRJ while in cruise flight from Syracuse to Atlanta - a fan blade on a CF34-3B1 turbofan engine fractured, causing a loud bang, severe vibration and, in one case, an engine fire.

Examination of the blades showed they failed because of a material defect introduced during the manufacturing process. GE says the titanium alloy blades were machined in Mexico by Teleflex Aerospace between late 2002 and late 2006 from billets containing a higher percentage of aluminium than was appropriate. "With a higher concentration of aluminium, there is a higher content of hard particles and this makes it more susceptible to cracks," it says.

A number of changes have taken place since the fan blade problem was identified. GE says it "went back and changed the billet sizes and melt specifications" and Teleflex is now building the fan blades to specification, "but when they received this billet, it had higher aluminum", says the engine maker.

Teleflex sold its Teleflex Aerospace Manufacturing Group unit to UK aerospace firm GKN in 2007.

The NTSB has issued six recommendations to the FAA, including that it require GE Aviation to define a reasonable maximum time frame below 4,717 cycles since new for these Teleflex fan blades and require that the blades be removed from service before that limit is exceeded. In the ASA incident, a fan blade failed after 4,717 cycles and 5,845 hours, which is "very early in a blade's service life", says the board.

The NTSB also wants the agency to require GE to include additional testing in the manufacturing process for those blades, and to make modifications in its CF34-1/-3 engine design to ensure that high engine vibrations - such as can happen when a fan blade fractures - will not cause the engine to catch fire.

The board also issued a recommendation to Transport Canada to require Bombardier to redesign the retention feature of the CRJ100/200 engine throttle gearbox to ensure it can withstand the loads generated by a fan blade separation or similar event.

"We are issuing this recommendation because we consider the safety risk associated with this condition to be unacceptably high," says NTSB chairman Mark Rosenker.

Bombardier could not provide immediate comment.