Accident Details
On July 3, 2014, at approximately 1846 central daylight time, a Cessna 336 (registration N3804U) experienced a partial loss of engine power and conducted a forced landing in Mobile, Alabama. The airline transport pilot was seriously injured, and the airplane sustained substantial damage. The aircraft was operated by the Mobile County Health Department. The flight was conducted under day visual meteorological conditions for a local public-use aerial application operation; no flight plan was filed. The flight originated from St. Elmo, Alabama (2R5) at about 1829.
Pilot's Account
According to a written statement provided to the NTSB, the pilot was assigned to mosquito control spraying in the Mobile area. He departed with approximately 48 gallons of fuel, including 36 gallons in the auxiliary tanks. While established on a southbound leg of the spray pattern, he transferred the engines, one at a time, to the full 18-gallon auxiliary tanks. Shortly after, the engines began to sputter and would not maintain RPM. He aborted the spray run, executed a zoom climb to about 600 feet above ground level, and turned toward Mobile Downtown Airport (BFM), about 4 to 5 nautical miles away. Available power was intermittent with RPM surges on both engines, and power appeared insufficient to reach BFM. He set up for a forced landing on an island between a container terminal and a coal terminal. The airplane touched down on soft soil and stopped abruptly, resulting in extensive damage.
In a subsequent interview on July 9, 2014, the pilot stated he had been flying at 100 feet agl when the rear engine began sputtering and coughing. Switching to the auxiliary fuel tank did not resolve the issue. He climbed to 500 feet agl and continued troubleshooting by switching tanks and turning on boost pumps. The front engine then began to lose power. He realized he could not maintain altitude and performed an emergency landing short of the airport.
Examination Findings
An FAA inspector examined the wreckage and confirmed structural damage to the fuselage. The fuel selector handle for the front engine was in the right main tank position; the rear engine fuel selector handle was broken off but later determined to also be in the right main tank position. The left and right main fuel tanks were empty, with only about 2 ounces of residual fuel drained from the sump tanks; the tanks were not breached. The left and right auxiliary tanks contained sufficient fuel, but the quantity was not quantified. Flaky, rust-colored debris was observed inside the right sump tank; the left sump tank was relatively clean. The wing auxiliary fuel pumps were functional when energized. Fuel lines from the selector valves to the tanks were unobstructed.
The rear engine fuel strainer bowl contained about 1/8 teaspoon of light gray, powder-like debris; the screen was unobstructed. The supply line from the strainer to the engine-driven fuel pump was obstructed; after clearing with a wire, about one teaspoon of similar debris was removed. The front engine fuel strainer bowl showed corrosion with a rust-like substance; the screen was unobstructed. The supply line was obstructed, and about one-half teaspoon of rust-colored, granular debris was removed.
Both engines were removed and sent to the manufacturer for examination. After repair of impact-related damage, both engines ran normally in a test cell and produced rated horsepower with no abnormalities.
According to the aircraft manufacturer, the auxiliary fuel tanks are intended for level, cruise flight and gravity-feed directly to the fuel strainer with no boost pumps. The Cessna 336 pilot's operating handbook states that main tanks should be selected during pre-flight inspection and before landing, and in an engine-out situation during flight, main tanks should be selected if auxiliary tanks are in use.