CEN24FA228

While enroute to the destination airport, the pilot reported a “cylinder temperature issue” to air traffic control (ATC) and the pilot diverted to another airport for a visual approach. The pilot overflew the airport and requested vectors for another visual approach. He then requested vectors to divert to an airport to the east before he informed air traffic control that the left engine lost power, and he received vectors back to the airport for a visual approach. The pilot maneuvered the airplane to land on runway 14, but for an unknown reason he decided to land on runway 32 instead. A pilot-rated witness reported that he observed the airplane while it was on the base to final turn for runway 32. He reported that the airplane’s wings leveled momentarily before it made a 60° left-bank turn and then entered a stall/spin in a counterclockwise rotation. The airplane impacted a trailer park about 0.38 miles from the approach end of runway 32. A postimpact fire ensued and destroyed the airplane. Examination of the airframe, flight controls, and the right engine did not detect any preimpact anomalies that would have precluded normal operation. Examination of the left engine found that the starter adapter spline was worn, with broken teeth on its crankshaft gear. The crankshaft gear remained properly timed with the crankshaft cluster gear, the investigation could not determine if the idler gear, which drives the magnetos, slipped timing. Mistiming of the magnetos could result in abnormal cylinder head temperature(s). In addition, there was improper hardware securing the cylinder No. 6 intake valve, which might have altered performance of that valve. Due to thermal damage, testing of the ignition and fuel systems could not be accomplished. Evidence of detonation was observed on the left engine’s piston heads. The installed engine data monitor was destroyed by the postimpact fire and did not provide further details as to the operational condition of the engine before the accident. Inspection of the starter adapter assembly is required annually by airworthiness directive and was accomplished on the most recent annual inspection. The airplane had flown about 5.5 hours since the inspection.

On October 5, 1996, the airplane was modified via supplemental type certificate (STC) SA00015SE, which installed vortex generators, “to improve stall characteristics and to reduce stall and Air Minimum Control (Vmca) speeds through control of boundary layer airflow.” Vmca is the minimum flight speed at which the airplane is controllable with a bank of 5° toward the operative engine with one engine inoperative and the remaining engine operating at takeoff power. Due to the installation of the STC, the Vmca was changed to 73 KIAS and superseded the airspeed listed in the emergency procedure below. The Pilot’s Operating Handbook, Emergency Procedures, Engine Inoperative Landing, stated: Figure 2. Engine Inoperative Landing Checklist A review of maintenance logbook entries found that both engines were rebuilt by the manufacturer in December 1992 and installed on the airplane in March 1993. Both engines had accrued about 1,459 hours total time at the last inspection, which was recorded on June 19, 2023. Using available ADS-B information, since the inspection the airplane flew 6 times for about 5.5 hours. On June 17, 2024, about 1623 mountain daylight time, a Cessna 421C airplane, N245T, was destroyed when it was involved in an accident near Steamboat Springs, Colorado. The pilot and passenger were fatally injured. The airplane was operated under the provisions of Title 14 Code of Federal Regulations Part 91 as a personal flight. ADS-B data recorded the airplane as it departed Vance Brand Airport (LMO), Longmont, Colorado, about 1515, and was enroute to Ogden-Hinckley Airport (OGD), Ogden, Utah. Transmissions made to ATC revealed that when the airplane was in the vicinity of Yampa, Colorado, about 1557, the pilot reported a “cylinder temperature issue,” and requested to divert to Steamboat Springs Airport/Bob Adams Field (SBS), Steamboat Springs, Colorado. ATC cleared the pilot for the visual approach to runway 14 at SBS. The airplane overflew SBS, and when queried about his intentions, the pilot initially requested vectors to realign with the airport but then requested to divert to Northern Colorado Regional Airport (FNL), Fort Collins/Loveland, Colorado. About 1609, while flying towards FNL, the pilot reported to ATC that the left engine lost power; ATC cleared the pilot back to SBS for a landing. Figure 1. ADS-B data showing the accident flight track. An employee at the fixed base operator at SBS was monitoring the universal communications frequency and reported that the pilot radioed a 4-mile final for runway 16, and shortly after the pilot reported that he was on the base leg for runway 32. At 1622:57, ADS-B data showed the airplane south-southwest of the runway about 825 ft above ground level (agl), heading 051° at 107 knots ground speed. The last recorded ADS-B data point was at 1623:03, when the airplane was about 135 ft agl, heading 040° at 40 knots ground speed. An airline transportation rated pilot reported that he observed the airplanewhile it was on the base to final turn for runway 32. He reported that the airplane’s wings leveled momentarily before it made a 60° left-bank turn and then entered a stall/spin in a counterclockwise rotation. The airplane impacted terrain and a postimpact fire ensued. An autopsy of the pilot was authorized by the Routt County Coroner. According to the autopsy report, the cause of death was multiple blunt force injuries, and the manner of death was accident. The FAA Forensic Sciences Laboratory performed toxicological testing on specimens from the pilot, which detected the presence of naproxen. Naproxen is a non-prescription, non-steroidal anti-inflammatory drug used to treat pain and inflammation. Density altitude was calculated to be about 10,207 ft. A review of the pilot’s logbook found that around March 2021, the pilot stopped making regular entries into his logbook. The last entry was dated December 28, 2021, which only listed the airplane tail number on a local flight for instrument flight rules dual training with no time provided. No further times were logged in his logbook. Using solely the hours logged in the logbook, the pilot had 383.2 total hours with 59.2 hours in make and model. On his most recent application for an FAA medical certificate dated September 13, 2023, the pilot reported having accrued 600 hours, with 10 hours in the preceding six months. His last flight review in the endorsement section of the logbook was dated July 11, 2022. It is unknown what airplane was flown for his last flight review; there was no ADS-B data available for the accident airplane or the pilot’s Cessna 414 on July 11, 2022. A telephone interview was conducted with the flight instructor who performed the pilot’s last flight review. She stated that she did not remember the accident pilot in great detail. She said that her normal multi-engine flight review would include several simulated engine out approaches. She stated that all her flight reviews are flown until the pilot meets or exceeds standards. She did not recall which airplane was used for the flight review. The airplane impacted terrain between two mobile homes about 0.4 miles from the approach end of runway 32. The airplane came to rest on a 180° magnetic heading and impact signatures were consistent with the airplane impacting in a near-horizontal attitude with little forward velocity. The main wreckage consisted of the entire airplane and both engines; all components remained relatively attached to the airplane. The propeller blades on the left engine appeared to be feathered. Most of the cockpit instrumentation and avionics devices were consumed by the postimpact fire, including the installed digital engine monitor. The flaps were found fully extended and the landing gear was found fully retracted. Flight control cable continuity was established from the control surfaces to the cockpit for the rudder, rudder trim, elevator, elevator trim, aileron trim, and flaps. Continuity from the leftaileron could be established to the cockpit but the right aileron cables both had a tensile separation aft of the wing locker. The ailerons and flaps were not observed; however, their attachment point hardware was found in the wreckage. The empennage control surfaces were all thermally damaged, but the attachment point hardware was found in the wreckage. The left fuel selector was located between the left and right main tank settings. The right fuel selector was selecting the left main tank. Both engines were removed from the airplane and shipped to Continental Aerospace Technologies, Mobile, Alabama, for further examination. Due to extensive thermal damage to the engines and accessories, neither engine could be run. Examination of the left engine found damage to the starter adapter spline and broken teeth on the crankshaft gear. The crankshaft gear remained properly timed with the crankshaft cluster gear; however, it could not be determined if the idler gear slipped timing. The idler gear is used to drive the magnetos. In addition, there was improper hardware securing the cylinder No. 6 intake valve. Due to thermal damage, testing of the ignition and fuel systems could not be accomplished. No anomalies were detected with the right engine. A review of maintenance logbook entries found that the starter adapter assembly was last examined in accordance with Airworthiness Directive 2007-05-15 on June 19, 2023, during a combined 100-hour and annual inspection.