Thousands of faulty fan blades found in CF34s

By: Gregory Polek

April 1, 2008
Engines

The NTSB last month sent recommendations to the FAA and Transport Canada to address a safety concern raised by two engine failures on Bombardier CRJ200s. The Board has determined that a flaw during the manufacturing process for fan blades led to the failure of the GE CF34-3B1 turbofans, and it wants procedures established to remove the suspect blades before another incident occurs.

In both cases–a July 27, 2006, engine failure on an Air Nostrum CRJ shortly after takeoff from Barcelona, Spain, and a May 24, 2007, engine failure on an Atlantic Southeast Airlines CRJ while in cruise flight from Syracuse to Atlanta–a fan blade 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.

Examination of the blades showed that they failed due to a material defect introduced during the manufacturing process. The manufacturer–Mexico’s Teleflex Aerospace Manufacturing Group–has produced more than 28,000 of the blades.
“We are issuing this recommendation because we consider the safety risk associated with this condition to be unacceptably high,” said NTSB chairman Mark Rosenker in a statement.

The ASA fan blade failed after 4,717 cycles and 5,845 hours.

The Board issued six recommendations to the FAA, including that it require GE Aviation to define a reasonable maximum time frame below 4,717 cycles and to replace all Teleflex blades that have reached that threshold. It also recommended that the FAA require GE to include further testing during the manufacturing process, and to modify the design of the CF34-1 and -3 engines to ensure that in the event a blade does break, the resulting engine vibration does not cause a fire.

Meanwhile, the Board has asked Transport Canada to require Bombardier to
redesign the retention feature of the CRJ 100/-200 engine throttle gearbox to ensure that it can withstand the loads generated by a fan blade separation or similar event.

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