NTSB: Corroded Engine VG Parts Caused Naples CL604 Crash

The NTSB released the final report today on the Hop-A-Jet Bombardier Challenger 604 crash on Feb. 9, 2024, in Naples, Florida. The probable cause of the accident cites corrosion in the jet’s GE CF34-3B engines' variable geometry (VG) system, which controls airflow through the high-pressure compressor by adjusting the position of the inlet guide vanes and the first five stages of stator vanes.

According to the NTSB, after both engines were sent to GE for post-crash evaluation, VG tests revealed “corrosion was observed in the high-pressure compressor (HPC) case flow path area, with the most significant corrosion found in the VG stage 5 area. Extensive corrosion was observed in the HPC case VG stage 5 stator vane spindle bores.

Additionally, the VG stage 5 stator vanes were unable to travel fully (that is, the distance from fully opened to fully closed) when tested using the specified maintenance procedures, and higher than normal actuation pressures were required to move the VG hardware through its full range when compared to other engines without corrosion on the HPC spindle bores, with a slower than normal VG system response when tested with pressurized air.

“At low power conditions, as was the case at the time of the accident, it can lead to sub-idle rotating stalls. It is likely the corrosion limited the VG hardware travel as the flight crew reduced the power for landing, resulting in near-simultaneous, sub-idle rotating compressor stalls and a subsequent loss of thrust in both engines, which was unrecoverable at the low altitude.”

Both pilots were killed in the accident, while the flight attendant and the two passengers on board were able to escape the aircraft before it was consumed by fire.

The probable cause of the accident was: “Corrosion of both engines’ variable geometry (VG) system components, which led to their operation in an off-schedule position and resulted in near-simultaneous sub-idle rotating compressor stalls on approach, subsequent loss of thrust in both engines, and an off-airport landing. Contributing to the accident was inadequate fault isolation guidance from the engine manufacturer, which prevented the identification of corrosion buildup in VG system components during troubleshooting of hung start events of both engines about one month before the accident.”