CEN23FA401

A partial loss of engine power due to fuel starvation caused by a fuel system blockage, and the flight instructor’s subsequent failure to maintain adequate airspeed after the loss of engine power, which resulted in the airplane exceeding its critical angle of attack and entering an aerodynamic stall at a low altitude.

The student pilot and his flight instructor were conducting touch-and-go landings during an instructional flight when a partial loss of engine power occurred during the initial climb from the runway. Two witnesses reported that they were on the ramp preparing for a flight when they heard a sudden decrease in engine rpm. They turned and saw the airplane flying about 500 ft above the runway in a level attitude with the wings rocking. The airplane then entered a left turn in a nose-down attitude. One of the witnesses believed that the pilot was attempting a descending left 180° turn to land on the opposite runway direction used for the takeoff. The airplane completed about 90° of turn when it entered an aerodynamic spin and descended to the ground in a nose-down attitude. Postaccident examination revealed debris that obstructed the inlet elbow fuel fitting to the fuel shutoff valve. Similar debris was also recovered from the fuel shutoff valve and the left and right fuel lines. Borescope examination of the fuel tanks revealed additional loose debris inside each fuel tank. Laboratory analysis determined the elemental composition of the fuel system debris consisted mostly of silicon, iron, and lead. Silicon and iron are consistent with soil. The presence of lead was consistent with transfer contact with fuel system components where leaded fuel, such as aviation 100 low-lead fuel, had been present. Based on the available evidence, the partial loss of engine power was likely due to fuel starvation from a blockage of the inlet elbow fuel fitting to the fuel shutoff valve. According to the airplane’s maintenance logbooks, the last maintenance of the fuel shutoff valve was completed more than 8 years before the accident. However, about 9 months before the accident, the fight instructor, who was also the airplane owner, made an entry in the airplane’s discrepancy record that the airplane was using fuel from the left tank “slower” than the right tank. The discrepancy was deferred until the next annual inspection. The discrepancy log entry further noted that the issue could not be duplicated during the annual inspection that was completed about 14 flight hours before the accident. Comparing the signatures on the discrepancy entry to signatures found in the flight instructor’s pilot logbook established that it was the flight instructor who entered and closed out the discrepancy entry. As described, the discrepancy was likely indicative of a fuel system blockage forming that resulted in uneven fuel usage between the left and right fuel tanks. The wreckage examination did not reveal any preimpact flight control or mechanical malfunctions or failures of the engine that would have prevented normal operation. The airplane’s nose-down attitude and aerodynamic spin are consistent with the flight instructor failing to maintain adequate airspeed during the return to the runway.

The airplane was equipped with a 26-gallon (22.5 gallons usable) fuel system, consisting of two 13-gallon main fuel tanks (11.25 gallons usable each). The two fuel tanks are combined before the fuel shutoff valve, as depicted in figure 1. On December 9, 2022, the fight instructor, who was also the airplane owner, made an entry in the airplane’s discrepancy record that the airplane was using fuel from the left tank “slower” than the right tank. The airframe total time was 8,024.9 hours at the time of the discrepancy. The discrepancy was deferred until the next annual inspection. The discrepancy log entry further noted that the issue could not be duplicated during the annual inspection dated August 15, 2023. The signature on the discrepancy entry was comparable to signatures found in the flight instructor’s pilot logbook. A postaccident review of the airplane’s maintenance logbooks revealed that the last maintenance of the fuel shutoff valve was completed about 8 years before the accident, on July 20, 2015, at 7,950.7 total airframe hours. The associated airframe logbook entry stated, in part, “Lubed fuel valve and installed new o-ring.” According to maintenance documentation, about 20 days before the accident, on August 15, 2023, the last annual inspection of the airplane was completed at 8,029 total airframe hours and 2,723.2 hours since the last engine overhaul. A 100-hour inspection was completed on August 23, 2023, after the airplane was painted. The airplane’s electronic tachometer was destroyed during impact. As such, the airplane’s total airframe and engine times at the time of the accident could not be precisely determined. However, according to an airplane utilization log, the last recorded flight was completed on September 4, 2023, at 8,041.4 hours total airframe time. Based on ADS-B flight track data, the accident flight was about 1.4 hours in duration. Figure 1. Fuel system schematic. The Fort Bend County Medical Examiner's Office performed the flight instructor’s autopsy at the request of a Walker County Justice of the Peace. According to the flight instructor’s autopsy report, his cause of death was blunt force injuries and the manner of death was accident. FAA Forensic Sciences Laboratory toxicological testing of postmortem specimens from the flight instructor did not detect any carboxyhemoglobin, ethanol, glucose, or tested-for drugs. The Fort Bend County Medical Examiner's Office performed the student pilot’s autopsy at the request of a Walker County Justice of the Peace. According to the student pilot’s autopsy report, his cause of death was blunt force injuries and the manner of death was accident. FAA toxicology testing did not detect any carboxyhemoglobin, ethanol, or glucose. The toxicology testing detected cetirizine at 24 ng/mL in cavity blood and at 631 ng/mL in urine. Metoprolol also was detected in cavity blood and urine. Cetirizine is a second-generation antihistamine medication that is available over the counter and is commonly used to treat allergy symptoms. Cetirizine often carries a warning that users may experience drowsiness and should be careful when driving a motor vehicle or operating machinery. Data on sedation and psychomotor impairment from cetirizine are mixed, with some studies finding some sedating and impairing effects. The FAA states that pilots should wait 48 hours after using cetirizine before flying to allow time for the drug to be cleared from circulation. Metoprolol is a prescription cardioselective beta-blocker medication that can be used as part of treatment for high blood pressure, certain arrhythmias, and certain types of heart failure. It sometimes also may be used for migraine headache prevention. Metoprolol is not generally considered impairing. The student pilot’s mother stated that her son had been diagnosed with hypertension and in the weeks before the accident he began taking medication to lower his blood pressure. She noted no other concerns pertaining to the student pilot’s health. On September 6, 2023, about 1148 central daylight time, a Cessna 150K airplane, N6059G, was substantially damaged during an accident at Huntsville Municipal Airport (UTS), Huntsville, Texas. The flight instructor and student pilot were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. According to ADS-B flight track data, at 1027 the airplane departed from runway 14 at North Houston Regional Airport (CXO), Conroe, Texas. The airplane flew northeast about 6 nautical miles before it turned northwest toward UTS. About 1050, the airplane entered the traffic pattern for runway 36 at UTS. The airplane flew 6 traffic patterns consistent with touch-and-go landings on runway 36. The airplane would descend below ADS-B coverage about 700 ft mean sea level (msl), or about 337 ft above airport elevation, while it operated in the traffic pattern at UTS. About 1128, the airplane switched landing direction to use runway 18. The airplane flew 3 additional traffic patterns consistent with touch-and-go landings on runway 18. At 1146:54, the last ADS-B return was recorded about 830 ft msl as the airplane descended on the base leg for runway 18. Two witnesses reported that the airplane was flying in the airport traffic pattern before the accident. They were on the ramp preparing for an instructional flight when they heard a sudden decrease in engine rpm. They turned and saw the airplane flying south over runway 18, about 500 ft above the runway, in a level pitch attitude with rocking wings. The airplane then entered a left turn toward east in a nose-down attitude. The flight instructor believed that the pilot of the airplane was attempting a descending left 180° turn to land on runway 36. He stated that the airplane completed about 90° of turn when it entered an aerodynamic spin and descended to the ground in a nose-down pitch attitude. The airplane crashed into an open grass area about 407 ft south of the end of runway 18 at UTS and about 40 ft east of the extended runway centerline. The airplane came to rest upright and nose down on a west heading. All structural components and flight control surfaces were located at the accident site. The left and right wings and their wing struts remained attached to their attachment points. The leading edge of both wings were crushed aft to their respective main spars. The tail was canted forward and to the right beginning about 3 ft aft of the rear cabin window. The empennage was relatively undamaged with minimal impact damage. The elevators, ailerons, rudder, trim tabs, and flaps were accounted for at the accident site. Continuity of the flight control cables was confirmed from the cockpit to the flight control surfaces. Continuity of the pitch trim control cables was confirmed from the cockpit to the trim surface. The cockpit control column assembly exhibited impact-related damage. The aileron control chain remained intact and partially attached to each control column sprocket. The aileron forward bellcrank/arm assembly remained attached to the control column with attached cables. The aileron balance cable remained continuous between the aileron bellcranks. The elevator control tube remained attached to the cockpit control column. The aft end of the elevator control tube was displaced aft about 6 inches and separated from the elevator forward bellcrank, which fractured into two halves with attached cables; the fracture exhibited signatures consistent with an overstress separation due to impact-related damage. The rudder cables were continuous from the cockpit pedals to the rudder control horn, where all hardware was present and connected. The left and right ailerons remained attached to their wing attachment points. The rudder remained attached to its attachment points on the vertical stabilizer. The left and right elevators remained attached to their