N6059G

HISTORY OF FLIGHTOn 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. AIRCRAFT INFORMATIONThe 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. AIRPORT INFORMATIONThe 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. WRECKAGE AND IMPACT INFORMATIONThe 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 respective horizontal stabilizer. The elevator trim actuator extension measured 1.4 inches and was consistent with a neutral pitch trim tab position.

The left and right flaps remained attached to their respective wing attachment points. The flap handle in the cockpit was found in the UP position. The flap actuator/motor was found in the fully retracted position and was consistent with fully retracted flaps at impact.

The wreckage examination did not reveal any preimpact flight control anomalies that would have prevented normal operation.

The left- and right-wing metal fuel tanks exhibited hydraulic deformation along the forward and top tank surfaces. The fuel tank finger strainer screens were not obstructed. The fuel lines from each wing fuel tank to the fuel shutoff valve assembly remained intact. The fuel lines from each wing fuel tank combined through a Y-shaped fuel fitting upstream of the fuel shutoff valve, as previously shown in figure 1. The fuel line from the fuel shutoff valve assembly to the fuel strainer assembly was impact separated about 2 inches forward of the fuel shutoff valve assembly. The fuel strainer assembly was displaced aft through the firewall into the cockpit floor area. The filter bowl was separated from the fuel strainer assembly and was impact damaged. The fuel strainer screen filter remained attached to the fuel strainer and exhibited debris. The fuel line from the fuel strainer assembly to the carburetor was separated and not observed.

The fuel line connected to the inlet port of the fuel shutoff valve was removed to examine the shutoff valve. There was fuel-wetted debris present that obstructed the inlet elbow fuel fitting, as shown in figure 2. The fuel shutoff valve outlet port exhibited accumulated debris affixed to its inside diameter, as shown in figure 3. Additional debris was recovered from inside the fuel shutoff valve when tapped on a table, as shown in figure 4.

Figure 2. Inlet to fuel shutoff valve.

Figure 3. Outlet of fuel shutoff valve.

Figure 4. Fuel shutoff valve with debris from inlet port.

The fuel line from each wing fuel tank was ...