General Electric (GE) intends to sell at steep discount CF34-3B1 engine fan blades to Bombardier CRJ operators that are impacted by a service bulletin, to be released tomorrow, calling for replacement blades to be installed over a two-year period.
"It's a shared expense," a GE spokesman told flightglobal.com's sister premium news site ATI during a follow-on interview this morning. "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 (NTSB) on 6 March issued recommendations to the FAA 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 takeoff 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 that they failed due to a material defect introduced during the manufacturing process.
Fan-blade supplier Teleflex Aerospace Manufacturing Group, a US-based company that sends machining to Mexico, received from "a certain shipper" a large billet of titanium alloy that contained a higher percent of aluminum than appropriate.
The result, says GE, is that hard particles "line up together" to form an aligned hard alpha and, over time, a crack can form.
"The bottom line is that with a higher concentration of aluminum, [there is a] higher content of hard particles and [this] makes it more susceptible to cracks," adds GE.
The defective blades were produced between late 2002 and late 2006. Diversified industrial firm Teleflex in 2007 sold its Teleflex Aerospace Manufacturing Group unit to UK aerospace firm GKN.
Teleflex Aerospace president John Suddarth says it would be inappropriate to comment on a firm that is no longer part of the Teleflex company.
GKN Aerospace in North America could not be immediately reached for comment.
A number of changes have taken place since the fan blade problem was identified. GE "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.
A population of 13,000 fan blades from CF34-3B1 engines that power CRJ200 aircraft have been identified by the engine manufacturer as being defective. Rough estimates show the blades are present on about 1,500 CF34-3B1 engines.
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 case of 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 that 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.
Source: flightglobal.com's sister premium news site Air Transport Intelligence news