NTSB Factual Report

On June 6, 2007, approximately 1100 central daylight time, a single-engine Air Tractor AT-401 agricultural airplane, N92PK, was substantially damaged during a forced landing following a loss of engine power while maneuvering near Oak Grove, Louisiana. The commercial pilot, sole occupant of the airplane, was not injured. The airplane was registered and operated by the Whittington Air and Ground LLC of Eudora, Arkansas. Visual meteorological conditions prevailed and no flight plan was filed for the aerial application flight conducted under 14 Code of Federal Regulations Part 137. The local flight originated from a private airstrip near Eudora, Arkansas, at 1015.

The 5,475-hour commercial pilot reported that after performing an aerial application pass, he initiated a turn to reverse direction to start another pass. At the top of the turn, the pilot "heard a loud bang, followed by a sound like something at high RPM was winding down, also noticed white smoke from the exhaust." The pilot subsequently reported a "noticeable loss of power," and noticed that the manifold pressure had "fallen to 16 or 17 inches."

Following the loss of engine power, the pilot executed a forced landing to a field. During the landing roll on the field, the tailwheel-equipped airplane rolled for "about 250 yards before turning upside down." The airplane came to rest in the inverted position and the pilot was able to egress the airplane unassisted.

According to the Federal Aviation Administration (FAA) inspector, who responded to the accident site, the horizontal stabilizer sustained structural damage.

The airplane was released to the owner after the accident, who later sold the airplane to another operator. Due to the damage sustained in the accident, the engine was disassembled and examined before the new owner could return the airplane back to service. The new owner provided a report of their findings from the engine disassembly. According to the Covington Aircraft, Radial Division Engine Investigation Report, "Undetermined causes resulted in distress to the phenolic separator bracket of the rear impeller support bearing resulted in its separation and fragmentation." This resulted in a chain reaction of events throughout the rest of the engine as clearances, lack of lubrication and subsequent wearing of engine components took place. This damage ultimately resulted in damage of the blower labyrinth seal and the impeller gear train, which reduced power output. According to the report, "the destroyed impeller drive gear train and the distress caused by the displaced blower spring drive mechanism, coupled with reduced power output, resulted in seizure of the propeller shaft/crankshaft and complete loss of power."

A review of engine's maintenance history revealed the 600 horsepower R-1340 radial engine had accumulated a total of 5,016.3 hours. The engine underwent a major overhaul 580.3 hours prior to the accident. The last major overhaul was performed as result of a propeller strike.

At 1053, the weather observation facility at the Monroe Regional Airport (MLU), near Monroe, Louisiana, located approximately 37 miles west-southwest of the accident site, reported wind variable from 150 degrees to 220 degrees at 10 knots, visibility 10 statute miles, clear skies, temperature 88 degrees Fahrenheit, dew point 68 degrees Fahrenheit, and a barometric pressure setting of 29.91 inches of Mercury.

NTSB Probable Cause

A complete loss of power due to failure of the impeller drive gear train and displacement of the blower spring drive mechanism, which resulted in seizure of the propeller shaft/crankshaft. Also causal was the failure of the phenolic separator bracket of the rear impeller support bearing for undetermined reasons. A factor was the none suitable terrain for the forced landing.