ERA24FA110

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 1 month before the accident.

The airplane was turning toward the final approach course about 5 miles northeast of the destination airport when a “Master Warning” light illuminated on the glareshield and, 1 second later, a corresponding red message was displayed on the engine indicating and crew alerting system (EICAS), with an “engine oil” voice advisory. Twenty-three seconds later, while the airplane was about 1,000 ft pressure altitude and 122 kts, on a shallow intercept angle for the final approach course, the crew announced to the airport air traffic control tower, “…lost both engines… emergency… (I’m/um) making an emergency landing.” The tower controller acknowledged the transmission and cleared the airplane to land. Shortly after, a flight crewmember replied, “eh we’re clear to land but we’re not gonna make the runway uh we’ve lost both engines.” The airplane touched down on a highway while in a slight left bank. It then veered right and travelled off the highway. The airplane’s right wing struck a non-frangible highway sign; the airplane then veered further to the right and impacted a concrete sound barrier wall. A postcrash fire ensued and the cabin attendant and two passengers were able to egress through the baggage compartment door in the tail section of the airplane. The two flight crewmembers were fatally injured and one ground occupant sustained a minor injury. Analysis of data from the flight data recorder (FDR) indicated that during the approach both engines began a commanded decrease in power, comparison of this deceleration to prior flights showed that the engine deceleration during the accident flight was consistent with previous flights and not consistent with a fuel cutoff event, combustor blowout, or engine flameout event. About 1 second after reaching the lowest engine core (N2) speeds of 62.8% (No. 1 engine) and 63.3% (No. 2 engine), N2 briefly increased to 65.0% (No. 1 engine) and 64.6% (No. 2 engine) consistent with the throttle command increasing. At that point, N2 rolled back on both engines and decreased to a sub-idle state, and interturbine temperature (ITT) increased for the rest of the recording. This behavior was consistent with both engine compressors operating in an unrecoverable rotating stall. Examination of both engines revealed no evidence of catastrophic internal mechanical failure. Fuel samples from various engine components, fuel supply lines, fuel tanks and the auxiliary power unit (APU) were collected and sent to two separate facilities for evaluation. The sampled fuel was consistent with normal Jet A fuel and no anomalies were noted. Operational testing of each main fuel control (MFC) unit indicated they were typical of an in-service MFC; no anomalies were noted that would have precluded normal operation. Both engines were sent to the manufacturer for further examination and disassembly, and a series of variable geometry (VG) tests were completed to assess the VG actuators’ total travel, actuation pressures, and rotational forces, and the VG system’s OPENED and CLOSED positions and drag torques. The examination revealed the same results for both engines: 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. This condition can have a significant negative impact on compressor stability during startup, which can lead to hung engine starts. 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. Chemical analysis of the corrosion collected from the compressor case and VG system hardware revealed corroded steel and elements commonly found in a sea salt environment. The corrosion buildup likely occurred over time as the airplane was continually exposed to salt air associated with marine climates. Since its manufacture, the airplane was primarily based at airports located in close proximity to the ocean (first with the previous operator based in Barbados, and then with the current operator based in Fort Lauderdale, Florida). Twenty-five days before the accident, a hung start occurred on both of the accident airplane’s engines while the pilots were preparing for taxi. The operator consulted with the engine manufacturer to troubleshoot the issue, using a fault isolation logic flowchart with 27 logic blocks requiring a “YES” or “NO” response. Block 21 of the flowchart required a pressure check of the VG system (titled Maintenance Practice [MP] 68). During the troubleshooting of the hung start events, MP 68 was not performed because the engines were started and no further anomalies were noted, allowing discontinuing of troubleshooting in accordance with the flowchart. With the concurrence of the engine manufacturer, the airplane was returned to service and flew 33 uneventful flights (excluding the accident flight) over the next 25 days, accruing 57 hours of flight time until the accident. According to the engine manufacturer, a hung start may be an indicator of corrosion buildup in the engine and will result in poor engine starting and operating performance. (In addition to the hung starts twenty-five days before the accident, the operator experienced 7 additional hung start events in the previous 10 years.) One way corrosion could have been identified in the engine, and specifically of the VG system components, was through the MP 68 pressure check. However, because this step was so late in the fault isolation hung start guidance, and it was not a required maintenance check, the airplane was returned to service after successful engine start and no other subsequent engine start issues. Thus, the corrosion of the VG system components continued to go undetected and eventually led to the sub-idle compressor stall during the accident flight. As a result of the accident investigation, the engine manufacturer published an updated version of the fault isolation hung start guidance to give precedence to the VG system testing by making it step 2 in the troubleshooting logic tree.

According to FAA and maintenance records, the airplane was manufactured in 2004 and was powered by two GE CF34-3B turbofan engines. It was operated by the previous owner from 2005 to 2020, during which time it was primarily based at Grantley Adams International Airport (BGI), Bridgetown, Barbados. The airplane was registered to the accident operator on May 21, 2020. It was then transferred to the accident operator’s FAA Part 135 certificate on June 3, 2021. At that time, the airplane and engines had accumulated about 6,939 hours since new (TSN) and 2,653 cycles since new (CSN). When the airplane departed OSU on the day of the accident, it had accumulated about 9,761 hours TSN and 4,444 CSN. During its duration with the accident operator, the airplane was primarily based at Fort Lauderdale Executive Airport (FXE), Fort Lauderdale, Florida, about 4 nautical miles west of the shoreline of the Atlantic Ocean. The airplane and engines were maintained under the operator’s FAA approved Continued Airworthiness Maintenance Program, which was established in accordance with Bombardier’s CL-604 Time Limits/Maintenance Checks Manual and GE’s service manual (SM) SEI-780. The accident engines were maintained and inspected on an “On-Condition” basis. (“On-Condition” refers to the corrective action required when testing or inspection finds an indication of a potential problem.) Previous Hung Start Event On January 15, 2024, (25 days before the accident), pilots reported intermittent hung starts on both engines while preparing for taxi. (A “hung start” is identified by light-off followed by abnormally slow acceleration and rotor speed [rpm] stabilization below idle. Hung starts may result from a variety of conditions, such as starter air pressure too low to accelerate the engine to a self-sustaining speed, premature starter deactivation, a poorly performing or damaged compressor, incorrect scheduling of bleeds or stator vane position, and fuel issues.) As part of the troubleshooting, fuel was drained from the engines and tested for contamination; none was found. The operator, in consultation with the engine manufacturer, spent several days troubleshooting the engines. Both engine fuel filters were replaced, and visual inspection of the old filters revealed no defects. On the following day (January 16, 2024), both engines started normally, and multiple functional checks were performed with no anomalies noted. The operator used GE SM SEI-780 72-00-00 (dated February 1, 2022 and titled “Fault Isolation 07 Hung Start or Slow Start”) to troubleshoot the engine. The troubleshooting fault isolation logic flowchart had 27 main logic blocks requiring a “YES” or “NO” response. Main logic block 21 referenced MP 68 to pressure check the VG system. The MP 68 pressure test was one of the last items in the troubleshooting tree. During the troubleshooting of the hung start events, MP 68 was not performed because the criteria of the flowchart were met to discontinue the testing (that is, the engines started and no anomalies were identified). With the concurrence of the engine manufacturer, the airplane was returned to service and both engines started and operated without issues for 33 flights over the next 25 days until the accident. Engine Trend Monitoring The operator participated in an engine trend monitoring program managed by the engine manufacturer. Certain engine parameters (such as N1 and N2 speeds, vibration levels, and oil temperature and pressure) and ambient conditions (such as airspeed and altitude) were collected and recorded for every flight, which the engine manufacturer analyzed to calculate takeoff exhaust gas temperature hot day margin and to monitor shifts in engine performance. For the CF34-3B task-oriented “On-Condition” maintenance program, Service Bulletin (SB) 71-1000 R01 directed the download and calculation of engine performance every 50 flight cycles for early detection of engine deterioration. The engine manufacturer did not issue any notices to the operator regarding trend monitoring data before or after the January 2024 hung starts on the accident engines. Captain The District Twenty Medical Examiner, Collier County, Florida, performed an autopsy of the captain. According to the autopsy report, the cause of death was inhalation of superheated gases and the manner of death was accident. Toxicology testing performed by the FAA Forensic Sciences Laboratory identified elevated carboxyhemoglobin at 25% and cyanide at 1.24 ug/mL in heart blood. Elevated carboxyhemoglobin and cyanide commonly are attributable to smoke inhalation, such as the autopsy report indicated occurred for the captain during the fire. In addition, quinine was detected in heart blood and urine. Quinine is the ingredient in tonic water that gives the beverage its bitter taste; it may also be used as a prescription medication. Although medicinal use of quinine may be associated with some adverse side effects, quinine is not typically impairing at levels associated with casual consumption of tonic water beverages. First Officer The District Twenty Medical Examiner, Collier County, Florida, performed an autopsy of the first officer. According to the autopsy report, the cause of death was catastrophic blunt force injuries, and the manner of death was accident. Postmortem toxicological testing conducted for the District Twenty Medical Examiner was unable to measure carboxyhemoglobin due to an unsuitable blood specimen; however, carboxyhemoglobin was reported to be elevated in congealed blood from the thermally injured heart, as assessed by a technique (microdiffusion) that relies on adding a chemical and observing a color change. Such a result can be attributed to effects of postcrash fire. Toxicology testing performed by the FAA Forensic Sciences Laboratory found no tested-for substances. The laboratory did not have blood available for carboxyhemoglobin testing. On February 9, 2024, about 1511 eastern standard time, a Bombardier CL-600-2B16 airplane, N823KD, was destroyed when it was involved in an accident near Naples, Florida. The two airline transport pilots were fatally injured. The cabin attendant and the two passengers sustained minor injuries, and one person on the ground suffered a minor injury. The airplane was operated by Ace Aviation Services (doing business as HopAJet) as a Title 14 Code of Federal Regulations Part 135 on-demand passenger flight. The airplane was returning to Naples Municipal Airport (APF), Naples, Florida, from Ohio State University Airport (OSU), Columbus, Ohio, where it had flown earlier in the day. The airplane was serviced with 350 gallons of fuel before departure from OSU. ADS-B flight track data and downloaded cockpit voice recorder (CVR) communications revealed that the flight crew contacted the APF air traffic control tower while on a right downwind leg of the approach to the airport and maneuvering for a 5-mile final approach to runway 23. About 1509, the tower controller cleared the flight to land. The airplane was about 6.5 miles north of APF, about 2,000 ft geometric altitude, and 166 kts ground speed, as it turned onto final approach for runway 23. Review of the data recovered from the airplane’s flight data recorder revealed that the first of three master warnings was recorded at 1509:33 (L ENGINE OIL PRESSURE), with the second immediately following at 1509:34 (R ENGINE OIL PRESSURE), and the third at 1509:40 (ENGINE). These warnings were annunciated by illumination of a “Master Warning” light on the glareshield, a corresponding red message on the EICAS, and a triplechime voice advisory (“Engine oil”). Twenty-three seconds later, at 1510:03, about 1,000 ft pressure altitude and 122 kts, on a shallow intercept angle for the final approach course, the crew announced, “…lost both engines… emergency… making an emergency landing” (see figure 1). The tower controller ackn