N1259MBeech 35-C33A · 1967

On June 1, 2024, at 1355 Pacific daylight time, a Beech 35-C33A airplane, N1259M, sustained substantial damage when it was involved in an accident near San Diego, California. The pilot and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot stated that the airplane’s fuel tanks were full when he departed on the approximate 330 nautical mile cross-country flight. He departed with the fuel selector positioned on the left tank and switched to the right fuel tank about 200 nm into the flight. During the landing approach, the pilot did not subsequently change the position of the fuel selector, and noted that, during the approach to the destination airport, the fuel quantity gauges indicated that the right tank contained more fuel than the left. The auxiliary fuel pump was off as required by the checklist.

The pilot stated that, about one mile from the runway on final approach, he fully extended the wing flaps. Shortly thereafter, the engine lost partial power and was “running rough.” The pilot enriched the mixture, but was unable to restore engine power. The pilot determined that the airplane was too low to reach the runway and prepared to make a forced landing short of the runway. The airplane landed hard, resulting in a nose gear collapse. During the accident sequence, the left wing sustained substantial damage.

Airplane maintenance records were not available. The pilot reported that the most recent annual inspection occurred in March 2024, about 26 flight hours before the accident.

The airplane was not equipped with an engine monitor. The pilot estimated landing with 14 gallons usable in the left tank and 24 gallons usable in the right tank.

Fuel System

The fuel system is designed for operation with 100 low lead aviation gasoline. The system includes a rubber fuel cell (bladder) in each wing leading edge with a flush-type filler cap. The airplane had an 80-gallon total fuel capacity (74 gallons usable). Each filler port had a visual measuring tab within the filler neck to estimate usable fuel with the wings level: 27 gallons at the bottom of the tab and 32 gallons at the detent. From the wing bladders, fuel is plumbed to a fuel selector, containing the Off, Left and Right positions. Fuel continues through a strainer, then through an electric auxiliary fuel pump before passing through the firewall and continuing to the engine-driven injector pump to a metering control unit and fuel manifold to the cylinder nozzles.

The fuel manifold valve body contains a fuel inlet, a diaphragm chamber, and outlet ports for fuel lines to the individual nozzles. The spring-loaded diaphragm includes a plunger in the central bore of the manifold body. The diaphragm is enclosed by a vented cover that retains the diaphragm loading spring. When the plunger is down in the body bore, fuel passages to the nozzles are closed off. The plunger is drilled to allow fuel to pass from the diaphragm chamber to its base and to the valve within the plunger. As fuel flow increases, pressure overcomes the diaphragm spring tension, causing the plunger to move to the open position, and fuel then flows from the manifold valve outlets through the fuel lines to the fuel nozzle assemblies.

During engine operation, approximately 10 gallons per hour of excess fuel returns to the selected tank. A check valve permits bypass of the engine-driven pump during starts or pump failures. A screen is installed at the tank outlet to trap large debris, and another screen is located at the inlet of the electric auxiliary pump to prevent contamination from entering downstream components. The fuel tanks are vented through lines that terminate in open ports on the bottom surface of each wing. These vents ensure continuous atmospheric pressure balance and prevent vacuum formation during fuel withdrawal.

Airplane maintenance records were not available. The pilot reported that the most recent annual inspection occurred in March 2024, about 26 flight hours before the accident.

The airplane was not equipped with an engine monitor. The pilot estimated landing with 14 gallons usable in the left tank and 24 gallons usable in the right tank.

Fuel System

The fuel system is designed for operation with 100 low lead aviation gasoline. The system includes a rubber fuel cell (bladder) in each wing leading edge with a flush-type filler cap. The airplane had an 80-gallon total fuel capacity (74 gallons usable). Each filler port had a visual measuring tab within the filler neck to estimate usable fuel with the wings level: 27 gallons at the bottom of the tab and 32 gallons at the detent. From the wing bladders, fuel is plumbed to a fuel selector, containing the Off, Left and Right positions. Fuel continues through a strainer, then through an electric auxiliary fuel pump before passing through the firewall and continuing to the engine-driven injector pump to a metering control unit and fuel manifold to the cylinder nozzles.

The fuel manifold valve body contains a fuel inlet, a diaphragm chamber, and outlet ports for fuel lines to the individual nozzles. The spring-loaded diaphragm includes a plunger in the central bore of the manifold body. The diaphragm is enclosed by a vented cover that retains the diaphragm loading spring. When the plunger is down in the body bore, fuel passages to the nozzles are closed off. The plunger is drilled to allow fuel to pass from the diaphragm chamber to its base and to the valve within the plunger. As fuel flow increases, pressure overcomes the diaphragm spring tension, causing the plunger to move to the open position, and fuel then flows from the manifold valve outlets through the fuel lines to the fuel nozzle assemblies.

During engine operation, approximately 10 gallons per hour of excess fuel returns to the selected tank. A check valve permits bypass of the engine-driven pump during starts or pump failures. A screen is installed at the tank outlet to trap large debris, and another screen is located at the inlet of the electric auxiliary pump to prevent contamination from entering downstream components. The fuel tanks are vented through lines that terminate in open ports on the bottom surface of each wing. These vents ensure continuous atmospheric pressure balance and prevent vacuum formation during fuel withdrawal.

Fuel System

The wings were previously removed for recovery purposes and stored outside. To test fuel system continuity, a small fuel tank containing new, clean fuel was connected to the left tank inlet and return. The electric fuel pump was disconnected at the splice adjacent to the unit. The fuel selector was tested and functioned correctly. Fuel flowed when selected to the left tank. When the selector was moved to the Right position, fuel flow ceased, consistent with the expected function. The fuel strainer screen was removed and found to contain areas of corrosion. The throttle and mixture control valve screen assembly was found free and clear of debris.

The fuel manifold was disassembled. The rubber diaphragm inside was found to be brittle, inflexible, and exhibited peeling on its upper surface. There were numerous flakes from the rubber found during the removal, but it could not be determined if the contaminants would have prohibited the venting of the unit. The vent hole was free of debris and there was no evidence of fuel leakage from the vent.

The fuel manifold screen was clean, but rust-colored. The manifold cavity displayed trace amounts of rust. The fuel strainer screen was removed and exhibited areas of corrosion. Fuel lines to each cylinder were disconnected and jars were placed under each line. Fuel flowed from each line at similar flow rates. The fuel injectors were removed and found clear of debris.

Continuity of the vent system was verified by blowing air pressure through the system. The vent line at the outboard section of the left wing was removed and air was introduced, resulting in fluid discharge consistent with water. The right wing vent system was similarly tested; pressurized air introduced at the inlet resulted in airflow out of the vent system and trace amounts of fluid exiting the lines. A water-detecting paste turned deep magenta when exposed to liquid recovered from the system, consistent with the presence of water. There was visible corrosion on the bottom of the fuel cap (filler) and receptacle screens.

Engine

Examination revealed no external damage to the engine crankcase. All six top spark plugs were removed and displayed gray coloration consistent with normal operation. Magneto-to-engine timing was confirmed with an engine timing light and was within normal operational range.

The cylinders’ combustion chambers were examined through the upper spark plug holes using a lighted borescope. The combustion chambers were mechanically undamaged, and there was no evidence of foreign object ingestion or detonation. There was no evidence of valve-to-piston face contact. The gas path and combustion signatures observed at the spark plugs, combustion chambers, and exhaust system components displayed coloration consistent with normal operation. There was no oil residue observed in the exhaust system gas path.

With the fuel still plumbed directly into the left wing root, an engine test run was performed. The engine operated for approximately five minutes between 1,200 and 1,700 rpm. A magneto check was conducted at 1,700 and 2,000 rpm. The engine operated normally during the test run.