The FAA has finalized a mandatory inspection program for GE CF34-8 engines to detect cracks in combustion liner outer shells that, if left to propagate, can cause the structure to buckle and, in extreme cases, trigger inflight shutdowns. 

Under an airworthiness directive set for publication Sept. 17, operators of engines with at least 17,500 flight hours (FH) since new or repair would have to perform a borescope or visual inspection within 500 FH. Depending on findings, follow-up inspections are required as frequently as every 300 FH. Shells with excessive cracking must be removed and replaced. 

The FAA’s inspection protocol is based on CF34-8C and CF34-8E service bulletins issued by GE in 2019. The directive affects about 1,500 engines on U.S.-registered aircraft—all larger Bombardier CRJs and Embraer E170-series models—though adoption by other regulators is likely. Aviation Week Fleet Discovery shows about 1,700 CF34-8s in the global fleet. 

At least eight engines have been removed “due to significant distress in the combustion outer liner shell,” GE explained in the bulletins. In two of the cases, the damage caused inflight shutdowns “due to severe thermal distress of the high-pressure turbine/low pressure turbine (LPT) hardware including burn through of the LPT case,” GE said. 

GE determined the root cause as a crack initiating at the trailing edge of one shell panel, propagating across an adjacent panel and into a third panel before meeting up with another crack. Possible ramifications include “buckling of the combustion outer liner shell as well as oxidation of large sections of it,” the service bulletins said. 

The inspections target the area where the cracks begin.