N656TEOstroth Thane L COZY MK IV · 2007

On January 14, 2024, about 1905 Pacific standard time, an experimental amateur-built Cozy MK IV airplane, N656TE, was destroyed when it was involved in an accident near Half Moon Bay, California. The pilot and two passengers were fatally injured and one passenger is presumed to be fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

A witness reported that while dining outside, north of the Half Moon Bay Airport (HAF), she heard the airplane and saw it shortly after. The witness said that the sound of the engine was similar to the sound of coughing, and that the airplane appeared to increase in speed while it was “dipping and turning.” The witness stated that the engine “cut out” and the airplane appeared to have banked toward the shoreline. Shortly thereafter she lost sight of the airplane’s lights.

Review of ADS-B derived data, provided by commercially available source, showed that the airplane departed runway 30 at HAF and entered a left turn just beyond the departure end of the runway. The airplane ascended to a maximum altitude of 250 ft msl, with groundspeeds fluctuating between 87 and 91 knots. The last recorded data point was recorded about 4,900 ft north of where wreckage was observed floating in the Pacific Ocean.

Review of a commercially available source of recorded common traffic advisory frequency communications revealed no radio transmissions from the pilot or any distress calls before, around, or after the time of the accident.

Figure 1: ADS-B Flight Overlay with Wreckage Locations

A witness submitted two security camera recordings captured from a camera mounted on his boat (see figure 2), located in a marina about 1 mile southeast of the approach end of runway 30 at HAF. The model of camera had an approximate 130° to 152° horizontal viewing angle.

Figure 2: Camera Location and Approximate Camera View Angles

Review of the submitted video, which began at 1903:35, revealed that about 20 seconds (1903:55) into the recording, the sound of an engine could be heard. The engine sound changed in pitch/tone about 46 seconds (1904:21) into the recording. About 1 minute, 10 seconds (1904:45) into the recording, the sound of the engine could no longer be heard. After about 1 minute, 27 seconds (1904:52), lights from what appeared to be from an aircraft entered the upper left area of the frame of video. The lights could be seen transitioning down and to the left side, out of the frame of the video, 39 seconds (1905:32) later, as seen in figures 3 and 4. The investigation was not able to determine if the lights were associated with the accident airplane.

Figure 3: Lights from an aircraft come into view of the camera.

Figure 4: Lights from an aircraft exit the view of the camera.

Review of the pilot’s digital logbook revealed that as of the last entry, dated January 1, 2024, the pilot had accumulated a total time of 2,549.0 hours, of which 209.2 hours were at night and 207.5 hours in the accident make/model airplane. The pilot had 388.34 hours of instrument flight time and 40.8 hours of actual instrument flight experience.

The airplane was equipped with 4 seats and dual flight controls and was powered by a Superior XP IO-360-B1A3 engine. The airplane had 2 fuel tanks, left and right, with capacity of 26 gallons each, totaling 52 gallons of fuel available. The airplane was last refueled nine days before the accident, with 39.43 gallons of fuel. A photo obtained from local law enforcement, captured on the flight inbound to HAF, captured the primary flight display, which indicated a total of 34 gallons of fuel on board (17 gallons per tank), with a fuel burn of 8.1 gallons an hour.

Maintenance records for the airplane were not located; however, draft logbook entries provided by a mechanic who performed maintenance on the airplane indicated an engine oil change at a Hobbs meter time of 818.2 hours. The mechanic further reported that the propeller was removed from the airplane and sent to a facility for overhaul, then reinstalled on the airplane in November 2023.

At 1855, recorded weather conditions at HAF included wind from 010° at 5 knots, visibility 6 miles, mist, broken ceiling at 300 ft agl, temperature of 10° C, dew point temperature of 9°C, and an altimeter setting of 30.12 inches of mercury (inHg).

At 1915, recorded weather at HAF was wind from 020° at 5 knots, visibility 5 miles, mist, broken ceiling at 300 ft agl, temperature of 9°C, dew point temperature of 9°C, and an altimeter setting of 30.11 inHg.

The airplane was equipped with 4 seats and dual flight controls and was powered by a Superior XP IO-360-B1A3 engine. The airplane had 2 fuel tanks, left and right, with capacity of 26 gallons each, totaling 52 gallons of fuel available. The airplane was last refueled nine days before the accident, with 39.43 gallons of fuel. A photo obtained from local law enforcement, captured on the flight inbound to HAF, captured the primary flight display, which indicated a total of 34 gallons of fuel on board (17 gallons per tank), with a fuel burn of 8.1 gallons an hour.

Maintenance records for the airplane were not located; however, draft logbook entries provided by a mechanic who performed maintenance on the airplane indicated an engine oil change at a Hobbs meter time of 818.2 hours. The mechanic further reported that the propeller was removed from the airplane and sent to a facility for overhaul, then reinstalled on the airplane in November 2023.

Sections of wreckage, including fragments of fiberglass, the center fuselage, right wing, canopy, engine, and propeller washed onto the shoreline about 2,130 ft west of HAF.

Figure 5: View of wreckage and debris washed on shore.

The fuselage was fragmented into multiple pieces. The center section was mostly intact with the exception of the forward part of the fuselage, in the area of the canards. Portions of ailerons were observed within the debris; however, the canards and a majority of the rudders were not located. Remains of the flight control system were observed; however, numerous separations of the control linkages were observed. All fractured areas were consistent with overload. Three of the four seat restraints were observed in the “buckled” position.

The engine was found upside down, partially embedded within sand and rocks. The engine remained attached to the engine mount; however, the engine mount was separated from the fuselage. The fuel inlet line from the airframe fuel pump to the engine was separated from the engine. A significant amount of rocks and sand was covering the engine. No holes were observed within the crankcase.

The engine-driven fuel pump was disassembled. The internal diaphragm was intact and undamaged. An odor of fuel was present when the pump was disassembled. The throttle plate and fuel control interconnect was intact and secure. The internal diaphragms were intact and undamaged. The throttle and mixture cables remained secure to their respective control arms.

The fuel flow divider, inlet fuel line, and outlet fuel lines remained attached to the engine; however, the fuel flow divider was compressed downward against the crankcase. No evidence of any fuel staining or leaks were observed at the fuel inlet and outlet lines. An FAA inspector removed the fuel flow divider and associated fuel lines from the engine. He stated that while he was removing the inlet fuel line, it was “loose” when using a wrench to remove the “B” nut. Additionally, the inspector noted that the “B nuts” on the 4 outlet ports were loose when removing them with a wrench. All 4 fuel injector lines were impact damaged. The flow divider was disassembled and the internal diaphragm and spring were intact.

Figure 6: View of the top side of the engine.

The crankshaft could be partially rotated by hand about 10 to 15 degrees using the propeller, with corresponding movement observed on the aft accessory gears. The propeller remained attached to the crankshaft. Two of the three propeller blades were separated about 8 inches outboard of the blade root.

Examination of the recovered wreckage revealed that the engine and most of the fuselage, wing structure, and remains of the ailerons and canards were recovered.

Continuity was established throughout the fuel system from the fuel selector valve to both the left and right fuel tanks. The left fuel tank appeared to be breached and the right fuel tank appeared to be intact.

The recovered instrument panel was fragmented into multiple sections. The primary flight display was not recovered. The magneto switch key was impact damaged; however, a portion of the key remained within the switch assembly and was in the “L” position.

The canopy was separated. A majority of the front area of the acrylic canopy was separated from the canopy structure. The right rear window was fractured. The left rear window was intact.

Examination of the recovered engine revealed varying degrees of impact damage and corrosion, consistent with saltwater submersion. Holes were drilled in the upper part of the crankcase and the internal areas of the crankcase were examined using a lighted borescope. No evidence of catastrophic failure was observed with any of the internal components.

The left and right magnetos were disassembled and inspected. The internal areas of both magnetos contained a significant amount of sand and exhibited varying degrees of corrosion. Some wear was observed on all electrode posts of the distributor blocks. The engine was equipped with a G3 electronic ignition system. Impact damage, saltwater submersion, and the airframe electrical system damage precluded functional testing of the ignition system.

The County of San Mateo Coroner’s Office performed the pilot’s autopsy. According to the pilot’s autopsy report, his cause of death was blunt trauma. The autopsy documentation indicated that the pilot’s body was recovered from water two weeks after the crash. Evidence of tissue breakdown was noted.

At the request of the Coroner’s Office, NMS Labs performed postmortem toxicological testing of liver tissue from the pilot. No tested-for substances were detected (ethanol was not detected at a reporting limit of 0.08 g/hg).

Postmortem toxicological testing by the FAA Forensic Sciences Laboratory detected ethanol at 0.016 g/hg in liver tissue, 0.037 g/hg in spleen tissue, and 0.024 g/hg in spleen tissue. No blood, vitreous fluid, or urine was available for FAA testing. Ethanol is the intoxicating alcohol in beer, wine, and liquor, and, if consumed, can impair judgment, psychomotor performance, cognition, and vigilance, with worse effects at higher blood ethanol levels.

FAA regulation imposes strict limits on flying after consuming ethanol, including a prohibition on piloting a civil aircraft while having a blood ethanol level of 0.04 g/dL or greater. Alcohol consumption is not the only possible source of ethanol in postmortem specimens. Ethanol may sometimes be produced by microbes in a person’s body after death, potentially elevating ethanol levels in some postmortem specimens more than others. Postmortem ethanol production is made more likely by extensive trauma and delayed recovery of remains, and prolonged water immersion can further complicate interpretation of postmortem ethanol results.