AD NPRM on CF34-3 Engine a Result of Hop-A-Jet Crash

The FAA has published a notice of proposed rulemaking (NPRM) for an airworthiness directive (AD) that would mandate tests and maintenance after hung starts for 1,152 CF34-1A, -3A/3A1/3A2, and -3B engines on U.S.-registered Bombardier Challenger 601s, 604s, 605s, and 650s. The AD is a result of the crash of a Hop-A-Jet Bombardier Challenger 604 on Feb. 9, 2024 ater a dual engine failure, and comments on the AD are due by June 15, 2026.

“The FAA is issuing this NPRM after determining that the unsafe condition described previously is likely to exist or develop on other products of the same type design,” according to the agency.

After the accident, “The engine manufacturer investigation revealed evidence of corrosion in the HPC [high-pressure compressor] module. Further analysis indicated corrosion in the HPC case vane boreholes traditionally associated with hardware that has been exposed to a saline environment, and pitting along the HPC case, with the worst corrosion in later stages from additional oxidation due to higher operating temperatures.

“While the investigation has yet to identify a definitive root cause, GE considers corrosion to be a contributing factor. Corrosion in the HPC case variable vane spindle bores can result in restricted range of motion of the VG [variable geometry] system, which can lead to compressor instability at or below idle speeds and potential loss of engine thrust control.

“As a result, GE published service material with inspection instructions to determine if the VG actuating system is obstructed by corrosion that can reduce its range of motion. This condition, if not addressed, could result in loss of engine thrust control and reduced control of the airplane.”

The AD would require, after a hung start, repetitive engine heat soak restart tests, according to the NPRM, and based on the tests, further troubleshooting and corrective actions. “This proposed AD would also require performing a borescope inspection (BSI) of the HPC case for corrosion and, depending on the results of the BSI, a VG system functional check for pressure evaluation. This proposed AD would also require, depending on inspection results, performing a force gage test on the feedback cable for tightness and a visual inspection of the VG system for obstruction and, if necessary, removal of the engine from service. This proposed AD would also require revising the ALS [airworthiness limitations section] of the existing engine maintenance manual to incorporate the VG system functional check.”

For operators of aircraft powered by these engines, the cost of compliance with the AD is estimated at 17 work hours for the testing, borescope inspection, and revision of the ALS. Each additional functional check or test is another eight hours for a possible total of 40 hours, plus, if necessary, 192 hours to replace an engine.