Mesaba Airlines

) FAA to include the use of remote diagnostics for vibration trends to detect cracked blades as an alternate to the visual and dimensional checks. FAA has accepted the use of trend monitoring programs to detect failures as evidence in AD 89-09-02 Rev 2. If the remote diagnostic system is inoperative the operators than can use the fan rub strip inspection method. This is very important since the NPRM paragraph f.2, f.3 & f.6 requires initial and repeat fan rub strip inspections. 2) The NPRM as written will require inspections of the fan rub strips within 20 cycles after the effective date of the AD. FAA is requiring the fan rub strip inspection based on when the fan blade was release from GE. The clock is started from cycles since new (CSN) for any engine containing any blade from the suspect population. Request that the fan rub strip inspection by diagnostics or visual check be ties to the effective date of the AD, 75 cycles, 100 hours which ever comes first then institute repetitive inspection until suspect fan blades are removed. This is in line with paragraph f.6 and g.10. Paragraph f.2 & f.3 should be removed from the AD. 3) FAA is assuming that Fan Blades are tracked on an individual, S/N basis, maintenance and inspections performed. The Fan Blades are not a life limited component as defined in the Chapter 05-11 nor is the inspection interval a mandatory requirement. Many operators have implemented a method to track maintenance actions and inspections performed on the fan blades. FAA needs to include process for determining cyclic limits if the fan blade cycles in service were not established when the fan blades were introduced into service. 4) The AD as written is far to complex in instructions for accomplishment of maintenance and the time/cycles allotted to comply with the AD. This operator is questiong why there was not separate ADs proposed for the RJ and BJ fleets. 5) Please define in the NPRM the CSLI & HSLI as it pertains to the fan rub strip inspection. 6) The SB 72-0250 for the Fan abradable Rub strip has a statement that requires PSE to be contacted if a rub has been observed, increase in depth but there is no indication of Fan blade Tang cracking. GE SB should be re written to be definitive It should not include this requirement.