FAA proposes rule to prevent cracking on certain CF34 models

Washington DC
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The US Federal Aviation Administration has proposed an airworthiness directive for certain General Electric CF34-10 fan rotor spinners and their supports, to prevent high cycle fatigue cracking that could lead to separation of the fan rotor spinner assembly and uncontained failure.

The proposed rule applies to 164 CF34 engines that power Embraer E-Jets with N-registrations, covering seven models, including -10E2A1, -10E5, -10E5A1, -10E6A1, -10E7 and -10E7-B.

The issue was first discovered on a CF34-10E engine following high fan frame vibrations, resulting in removal of the fan rotor spinner, which revealed eight of 12 attachment lugs on the spinner were cracked.

The cause of the vibration, said the FAA, was determined to be "a non-synchronous vibration" which was traced to a redesign of the spinner that "removed an interference between the fan blade retainers and the spinner".

If not corrected, the high-cycle fatigue cracking of the fan rotor spinner support attachment lugs could result in an uncontained engine failure and damage to the aircraft.

The rule comes in conjunction with a 31 January service bulletin from GE, which calls for replacement of the fan rotor blade retainers that "reintroduce the interference between the fan blade retainers and the spinner".

The FAA estimates a two-hour per engine process of compliance, with a cost of $10,458 per engine with parts and labour, with a total cost to US operators of $1.74 million.

The proposed directive calls for replacement of the fan rotor blade retainers within 1,800 in-service hours after the airworthiness directive becomes effective.