Operators of an estimated 616 US-registered aircraft powered by Rolls-Royce AE3007 engines will be required to perform initial and recurring compressor checks on the turbofans to prevent possible uncontained engine failures under an airworthiness directive (AD) to be issued by the US FAA on 2 November.
Along with a variety of business jets and military aircraft, the AE3007 powers the Embraer ERJ-135/140/145 twinjet family.
The AD, set to become effective on 17 November, will require an eddy current inspection of the outer circumference on the hub wheels of the sixth through 13th stages of the 14-stage compressor in search of cracks. The FAA said it received "reports of low-cycle fatigue cracks" on the parts during shop visits.
The problem, flagged up by Rolls-Royce in June through an alert service bulletin, has been found on wheels having both chrome-carbide coated knife edge seals as well as those without the coating.
"These cracks can deteriorate the integrity of the compressor wheel by lengthening into the outer circumference of the wheel," said the FAA in an advance copy of the final rule. "This condition, if not corrected, could result in uncontained failure of the 6th-13th stage compressor wheel, leading to damage to the airplane."
Along with an initial inspection, the timing of which is function of the number of engine cycles since new and the knife edge seal coating, engines must receive a follow-up inspection every 5,000 cycles. Wheels found to be damaged must be replaced.
Highest time engines, those with more than 18,185 cycles and using chrome-carbide coated knife edge seals must be inspected with 15 cycles.
The FAA estimates that the inspections and potential wheel change outs will cost US operators more than $36 million.
The FAA in 2009 issued an emergency AD requiring inspections on the two-stage high pressure turbines for the AE3007 based on reports of cracks being found.
Source: Air Transport Intelligence news