A safety concern raised by two engine failures on General Electric (GE) CF34-powered Bombardier CRJ200 aircraft has prompted the US National Transportation Safety Board (NTSB) to issue recommendations to the FAA to ensure procedures are in place to remove defective fan blades before another incident occurs.

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

A companion recommendation was sent to the Canadian government.

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.

Both flight crews declared emergencies and landed safely with no injuries. In the latter incident, the ASA fan blade failed after 4,717 cycles and 5,845 hours, which is "very early in a blade's service life", says the board.

Examination of the blades showed that they failed due to "a material defect" introduced during the manufacturing process. The fan blades were manufactured by Mexico-based Teleflex Aerospace Manufacturing Group, which has produced more than 28,000 of these blades.

In response to this finding, the board 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.

It 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.

Source: flightglobal.com's sister premium news site Air Transport Intelligence news

See a picture of GE Aviation's CF34 engine and more information about which aircraft uses this engine type

Source: FlightGlobal.com