This is a copy of the original post body for posterity:

TL;DR: Salt-air corrosion in the HPC variable-geometry stator vane spindle bores of both GE CF34-3B engines jammed the VGs in an off-schedule position. Power reduction for landing triggered simultaneous unrecoverable sub-idle compressor stalls in both engines. GE's hung-start troubleshooting flowchart buried the one test that could have caught it (MP 68) at block 21, so months of warning signs were missed. Coastal-based CF34-BJ operators — check your SBs.

Aircraft: Bombardier CL-600-2B16 (Challenger 604), N823KD, operated by Ace Aviation Services dba Hop-A-Jet, Part 135 on-demand. GE CF34-3B engines.

Outcome: Both pilots fatal. Cabin attendant + 2 pax minor injuries. 1 minor ground injury. Aircraft destroyed by post-crash fire after striking a highway sign and concrete sound barrier on I-75.

Probable Cause (verbatim from NTSB):

▎ 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 was inadequate fault

▎ isolation guidance from the engine manufacturer, which prevented identification of corrosion buildup in VGsystem components during troubleshooting of hung start events on both engines about 1 month before theaccident.

What actually happened (the short version):

- On a shallow intercept to final for RWY 23 at KAPF, crew reduced power for landing. As N2 rolled back toward idle, both engines simultaneously entered a sub-idle, unrecoverable rotating compressor stall. ITT spiked past 889°C redline. Master warning, L+R engine oil pressure warnings, then "ENGINE" warning fired within

7 seconds.

- FDR showed behavior was NOT a fuel cutoff, combustor blowout, or flameout. It looked exactly like the hung-start rollbacks the same two engines had 25 days earlier.

- Crew declared "lost both engines" at \~1,000 ft / 122 kts. Couldn't make the runway. Touched down on southbound I-75, veered right, clipped a highway sign, hit a sound wall. Cabin attendant egressed 2 pax through the baggage door (she only knew how because she'd helped load bags before — her training did not cover that exit).

Why the engines rolled back — the root cause:

- Teardown of both engines showed extensive corrosion in the HPC case, specifically in the stage-5 statorvane spindle bores. Chemical analysis: steel corrosion + chlorine/sulfur/sodium/calcium/potassium/magnesium = classic sea salt / marine environment exposure. Aircraft had spent its life at coastal airports

(Barbados, then Fort Lauderdale Executive, \~4 nm from the Atlantic).

- Corrosion prevented the VG stage-5 stator vanes from traveling their full range and required higher-than-normal actuation pressures. That put the VGs in an off-schedule position. At low power (like power-reduction for landing), that = compressor instability = rotating stall. Unrecoverable at low altitude.

- Fuel was fine. MFCs were fine. No fuel contamination (tested for SAP, Kathon, DEF — all clean). No mechanical failure. It was purely the VG system hung up on corroded spindle bores.

The damning part — it was findable, and GE's troubleshooting flowchart missed it:

- 25 days before the crash, both engines had hung starts (Jan 15, 2024). Operator worked with GE using SM SEI-780 "Fault Isolation 07 Hung Start or Slow Start" — a 27-block YES/NO flowchart.

- The VG pressure check (MP 68) that would have caught the corrosion was Block 21 — near the end of the tree.

- Since the engines successfully started the next day and showed no other anomalies, the flowchart let them exit troubleshooting before ever reaching MP 68. GE concurred with returning the airplane to service. It flew 33 uneventful flights / 57 hours before the accident.

- History: this airframe had 7 additional hung starts in the preceding 10 years — all handled the same way.

NTSB Findings categories:

- Aircraft: Fatigue/wear/corrosion

- Aircraft: Malfunction

- Organizational: Adequacy of manufacturer policy/procedure

- Environmental: Contributed to outcome

Safety actions GE has since taken:

1. SB 72-0345 R00 (May 2024) — one-time VG functional check on any CF34-BJ engine with a hung start in the previous 24 months. As of May 2025: 34 engines inspected, 7 failed and were pulled from service (4 of the 7 were from the accident operator's fleet).

2. SB 72-0347 R00 (May 2025) — one-time borescope + VG functional check of HPC stages 5/6 on all CF34-3BJ engines within 48 months. As of Mar 2026: 1,085 inspected, 1 failed.

3. SB 71-0000 R03 (Feb 2026) — new special requirements for sea/salt environment ops or engines showing external corrosion.

4. Adding a recurring HPC case BSI + VG Functional Check (MP 68) every 48 months to the Airworthiness Limitations section of SM SEI-780.

5. Aug 2024 — revised Fault Isolation 07 to make the MP 68 VG pressure check one of the first steps instead of Block 21.

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[Source](https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193769/pdf)

NTSB Aviation Investigation Final Report, Accident No. ERA24FA110, adopted 4/24/2026.

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