CEN23FA284

The multi-engine airplane was in level flight at 5,000 ft on a north heading toward the destination airport. Onboard data indicated the right engine’s fuel flow fluctuated for about 15 seconds. About 20 seconds later, the left engine fuel flow reduced to zero. The airplane made a slow descent toward the east for about 9 minutes, away from the destination airport. The airplane then turned west back toward the airport and continued a slow descent. About 10 minutes later, the airplane was less than 100 ft above ground level, with a groundspeed of about 61 knots. The airplane turned left about 40° during the last 4 seconds of recorded data and subsequently impacted a field with a nose-down attitude. The airplane sustained substantial damage to the fuselage, empennage, and both wings. Postaccident examination of the airplane revealed the left engine’s fuel selector was in the off position and right engine’s fuel selector valve was in the main tank position. The right fuel selector valve was corroded, which most likely resulted in the right engine fuel flow fluctuations. It is possible that the pilot moved the left engine fuel selector from auxiliary tank to off inadvertently when he intended to move the right engine’s fuel selector from the auxiliary tank to the main tank. The left-engine propeller was not feathered at the accident site, which resulted in additional in-flight drag and a higher minimum controllable airspeed (VMC). During the attempted forced landing, the pilot failed to maintain adequate airspeed, which resulted in a loss of control and a nose-down impact with terrain. The pilot’s toxicology results indicated use of the sedating antihistamine medication diphenhydramine, and he may have experienced associated impairing effects at the time of the accident. More precise interpretation of the diphenhydramine level in cavity blood was not possible. The pilot also had used other drugs that may have had adverse side effects (yohimbine, as well as both tadalafil and tamsulosin), although there was no way to determine whether such side effects were present or significant. The investigation was not able to determine the role the pilot’s medication usage may have played in the accident sequence.

The airplane is equipped with four integral fuel cells located in the leading-edge sections of the wings. Capacity of the two main fuel cells is 30 gallons each, of which 27 gallons is usable. The auxiliary fuel system consists of two 15-gallon cells (all usable) installed in the wings just outboard of the main fuel cells. The airplane also had wingtip tanks with a capacity of 15 gallons each that are connected to the adjacent auxiliary fuel cells. The left and right engine fuel selector valves enable fuel to be drawn from any of the fuel cells to both engines. The fuel selector valve positions are main, auxiliary, crossfeed, and off. Positioning of the left versus right fuel selectors involves a rotation in the opposite direction (see Figure 1). Figure 1. Diagram of Left and Right Fuel Selector Valves On July 8, 2023, about 0941 central daylight time, a Piper PA-30, N4743M, was substantially damaged when it was involved in an accident near Sherman, Texas. The pilot sustained fatal injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to automatic dependent surveillance-broadcast (ADS-B) information, the airplane departed Aero Country Airport (T31), McKinney, Texas, at 0902 and proceeded toward Sherman Municipal Airport (SWI), Sherman, Texas, about 5,000 ft mean sea level (msl). At 0919:20, while the airplane was level on a northerly heading toward SWI, onboard data indicated the right engine’s fuel flow fluctuated for about 15 seconds. At 0919:55, the left engine’s fuel flow rapidly dropped to zero and the left engine cylinder head and exhaust gas temperatures decreased. At 0921:55, about 6 miles southeast of SWI, the airplane started an orbit to the right, then began a shallow descent on an easterly heading away from SWI. About 0926, the left engine’s fuel flow rapidly increased, then dropped back to zero for the remainder of the flight. The airplane continued a shallow descent on easterly and northeasterly headings. About 0931 and 13 miles east of SWI, the airplane turned left and continued a shallow descent while on westerly and southwesterly headings. About 0941, the last ADS-B data showed the airplane at 61 knots and less than 100 ft above ground level. The airplane was about 250 ft northeast of the accident site. During the last 4 seconds of recorded data, the airplane turned left about 40°. An autopsy of the pilot was performed by the Southwestern Institute of Forensic Sciences at Dallas Office of the Medical Examiner, Dallas, Texas. The cause of death was blunt force injuries. Toxicological testing by the Federal Aviation Administration (FAA) Forensic Sciences laboratory detected diphenhydramine in urine and at 70 ng/mL in cavity blood. Diphenhydramine is a sedating antihistamine medication widely available over the counter in multiple sleep aids and cold and allergy products. Diphenhydramine can cause cognitive and psychomotor slowing and drowsiness. The FAA states that pilotsshould not fly within 60 hours of using diphenhydramine to allow time for it to be cleared from circulation. Diphenhydramine concentrations in postmortem cavity blood cannot be directly compared to established ranges in living individuals because diphenhydramine has substantial potential for postmortem redistribution and cavity blood has a potential to be diluted or contaminated by other body fluids. Toxicology testing by the FAA also detected tadalafil, yohimbine, tamsulosin, and acetaminophen in cavity blood and urine. Descriptions of these medications and their potential for flying impairment are discussed in the NTSB Medical Factual Report, located in the docket for this investigation. No alcohol was detected in cavity blood. The airplane impacted a field on a southwest heading and came to rest upright about 50 ft beyond the initial impact crater. Both propellers were buried in soft soil near the impact crater and had minimal indications of scoring or rotational energy. All propeller blades were near the low pitch stop (not feathered). The forward fuselage was crushed consistent with a nose-down impact. The landing gear and flaps were in the retracted position. No anomalies were observed with the flight control system. About 9 gallons of fuel were recovered from the left main fuel cell and about 11 gallons from the left auxiliary fuel cell. About 9 gallons were recovered from the right main fuel cell and about 3 gallons from the right auxiliary fuel cell. No fuel was recovered from either wing tip tank. Both electric fuel pump switches were in the on position. The fuel filler caps were not worn or damaged and the rubber sealing surfaces were not cracked. The left fuel selector handle was found in the off position and the right fuel selector handle was found in the main tank position. Fuel sampled from the left fuel selector contained a minimal flake of corrosion and did not illicit a reaction from water finding paste. Fuel sampled from the right fuel selector contained multiple rust flakes and a bead of water and the fuel drained very slowly. The right fuel selector was disassembled, which revealed rust and water that partially blocked the filter elements. The right fuel selector was tested with low air pressure, which revealed partial blockage to the right auxiliary fuel tank port, and air could pass through that port when the handle was selected either to the off or main tank position. The right fuel selector handle was difficult to move and produced a grinding sound when turned. Both engines were examined, which revealed normal crankshaft rotation, with suction and compression obtained from all cylinders. The magnetos of both engines produced sparks at all posts when manually rotated. The left engine servo fuel screen was free of debris. The right engine servo fuel screen contained rust particles but was not blocked.