The NTSB’s final report released Friday says corrosion in both engines’ variable geometry systems led to the Feb. 9, 2024, accident of a Hop-A-Jet Bombardier Challenger 604 on Interstate 75 near Naples, Florida. Both pilots were killed, and the cabin attendant, two passengers and one person on the ground were injured. The Part 135 flight was arriving at Naples Municipal Airport from Columbus, Ohio, when the crew reported losing thrust in both engines about 5 miles from the airport.
Hung Starts Preceded Accident
“Corrosion of both engines’ variable geometry (VG) system components,” the NTSB said, caused the systems to operate out of position, resulting in “near-simultaneous sub-idle rotating compressor stalls on approach, subsequent loss of thrust in both engines, and an off-airport landing.”
For those more familiar with piston engines, the issue described in the report is somewhat analogous to a problem with airflow management, as opposed to fuel or ignition. In a turbine engine, internal vanes adjust to control how air moves through the compressor at different power settings. If those vanes don’t move properly—due to corrosion in this case—the airflow can become unstable, especially at low power, leading to a loss of thrust even though the engine has fuel and no major mechanical failure.
Investigators said the aircraft had recently experienced intermittent hung starts on both of its GE CF34-3B engines weeks earlier, on Jan. 15, 2024. The flight’s operator, Ace Aviation Services, which was doing business as Hop-A-Jet, worked with GE Aerospace to troubleshoot the issue, but the variable geometry system pressure check was not performed because the engines later started normally and the flowchart allowed the troubleshooting to stop.
The aircraft then flew 33 uneventful flights over the next 25 days.
Salt Exposure Cited
The NTSB said both engines showed corrosion in the high-pressure compressor case flow path, with the most significant corrosion around the stage 5 variable geometry stator vane area. Chemical analysis found elements consistent with a marine salt environment. The aircraft had previously been based in Barbados and later at Fort Lauderdale Executive Airport, about 4 nautical miles from the Atlantic shoreline.
The report said fuel testing did not identify contamination, the main fuel controls showed no anomalies that would have prevented normal operation, and flight data did not support a fuel cutoff, flameout or combustor blowout. GE later revised its hung-start troubleshooting guidance to move the variable geometry pressure check near the beginning of the process and issued several service bulletins and inspection recommendations for CF34 business jet engines.
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