Accident Sequence
On January 4, 2020, at about 1009 Pacific standard time, an experimental amateur-built TM-1 Thunder Mustang airplane, registered N151WR, was destroyed in an accident near Santa Clarita, California. The pilot was fatally injured. The flight was conducted under 14 Code of Federal Regulations Part 91 as a personal flight.
The airplane was cleared for takeoff and instructed to maintain at or below 2,500 ft mean sea level until north of the airport. After departure, the pilot was approved for a frequency change. However, the airplane turned back toward the airport, and the pilot reestablished communication with the tower controller, reporting smoke from the right exhaust stack. He stated he would have to land and advised the controller of his position over Newhall. The pilot further reported that he could not see anything and had lost engine power. After the controller acknowledged, the pilot began to say he would have to put the airplane down, at which point the transmission was cut off.
A witness observed the airplane maneuvering at low altitude with smoke trailing from it just before impact. The airplane appeared to be under control. It struck a tall tree and came to rest in a grassy field located in the median of an interstate off-ramp cloverleaf roadway.
Aircraft and Wreckage Information
The low-wing airplane was powered by a Falconer V12 liquid-cooled engine equipped with a four-bladed variable-pitch propeller. The airframe and engine logbooks were not located during the investigation.
Examination of the accident site revealed that the airplane impacted level terrain in a median on a freeway exit ramp. Several tall trees were present on the east side of the median. Near the top of a tree about 60 ft tall, several branches were broken with fresh breaks, and a section of the airplane was embedded in the tree. Parts of the propeller blades were found at the base of the tree. The right wing tip and wing parts were also near the initial tree impact. The wreckage came to rest upright on a magnetic heading of about 140°, approximately 75 ft past the initial impact. All major components were within the main wreckage site. Most debris consisted of small fragments of the canopy and sheared-off landing gear. A postimpact fire thermally damaged most of the airplane and engine. Flight control continuity could not be verified due to thermal and impact damage.
Engine Examination
The engine was examined at a secure facility. All engine components and accessories were present and attached. The engine sustained thermal and impact damage, including damage to the engine mount support tubes, and would not rotate. A borescope inspection revealed that the six cylinders on the right side of the engine had normal operating conditions, while several cylinders on the left side—Nos. 1, 3, and 5—were nearly black in color.
The intake manifold, valve cover, and intake plenum were removed. The exhaust valve push rod for No. 5 cylinder was not secured and was found lying inside the engine. The left side head assembly was removed, revealing that the Nos. 1, 3, and 5 cylinder head attachment areas had material deformation consistent with an internal combustion gas leak. No. 1 cylinder had material deformation through a coolant passageway and the crankcase, with a hole about 1 cm wide by 3 ml deep (as stated in the source). Discoloration and material deformation near the hole were consistent with extreme hot combustion gases. On Nos. 3 and 5 cylinders, the hot combustion gases had penetrated only into the coolant passageway and had not burned through the crankcase.
All spark plugs were removed. The electrodes of spark plugs for cylinders Nos. 1, 3, and 5 were very black, oily, and carbon fouled, with No. 1 significantly darker; the others appeared normal according to the Champion Check-A-Plug chart. Engine disassembly revealed that the piston tops and cylinder heads were absent of carbon buildup and had a sandblasted appearance consistent with detonation. The cylinders exhibited damage consistent with detonation at the cylinder head and piston face edges. Traces of oil were present, but no coolant was observed in the engine. The fuel manifold and fuel injectors showed no anomalies or obstructions except thermal damage. No additional preimpact mechanical anomalies or malfunctions were found.
Medical and Toxicological Information
An autopsy conducted by the Los Angeles County Department of Medical Examiner determined the cause of death as multiple blunt force injuries. The FAA's Forensic Sciences Research Laboratory performed toxicological testing, which was negative except for positive results for glucose (in vitreous and urine, with no reported history of diabetes mellitus) and Tamsulosin, a prescription alpha blocker used for enlarged prostate symptoms, generally considered acceptable for airmen.