NTSB Factual Report

On May 18, 2010, at 1630 Pacific daylight time, an Ayres Corporation S2R, N29254, experienced a loss of engine power while maneuvering to spray a field, and struck power poles while attempting a forced landing near Glenn, California. Alaska Air Service, LLC., operated the airplane under the provisions of Title 14 Code of Federal Regulations Part 137 as an aerial application flight. The commercial pilot, the sole occupant, was not injured; the airplane sustained substantial damage to the fuselage and wings. Visual meteorological conditions prevailed for the local area flight, and no flight plan had been filed.

According to the pilot, he was on his second spraying run to the field when smoke started to emanate from the engine compartment, and then the engine "rolled down." He chose an adjacent road to make the emergency landing, and began making S-turns to line-up with the road while he lowered the flaps. He crossed power lines in a slight left turn, and touched down on the pavement. He could not prevent the airplane from turning left, and it impacted power poles; the landing gear was sheared off. It came to rest between the road and an orchard.

The engine was examined by Pratt & Whitney Canada (PWC) personnel under the supervision of the Federal Aviation Administration. The complete examination report is part of the public docket. They discovered no anomalies that would have precluded normal operation. It was noted that both the large and small exit ducts exhibited discoloration, and heat erosion to the inner dome area, as well as some localized burning. The visual inspection of the fuel control unit exhibited soiling of the body, along with visible surface corrosion on the exposed steel components. PWC personnel also noted bearing grease depletion on the driveshaft bearing plate.

During the inspection of the fuel nozzles, PWC personnel found that the nozzle tips were soot and soil coated, with surface corrosion evident; the number 8 inlet adapter was wet. Tab washers were present at each nozzle tip. PWC personnel tested the nozzles in accordance with test record sheet TR2010 Rev. 04 (engine overhaul manual 3011403 Rev. 23). It was noted that all of the fuel nozzles were out of limits. PWC stated that the observations noted during the test may cause hot-section deterioration over time, but would not prevent normal operation of the engine.

A fuel sample from the accident airplane was collected during the engine teardown by the engine manufacturer. The exact type of fuel was not known but the presence of an off-road/agricultural use #2 diesel fuel was suspected due to the red color of the sample. The sample was sent to an independent, third party laboratory for analysis. The sample was tested in accordance to ASTM D2887- Standard Test Method for Boiling Range Distribution of Petroleum Fractions by Gas Chromatography. It was determined that sample was a mixture of Jet “A” and off-road #2 diesel fuel. The third party laboratory report including the chart of known fuels boiling point fraction is contained in the public docket.

An inspection of the Compressor Turbine (CT) Guide Vane Ring exhibited damage and erosion. The CT was shipped to the National Transportation Safety Board Materials Laboratory for further examination.

The NTSB Materials Laboratory complete report is part of the public docket. The longer fractured blades displayed similar characteristics with oxidized fractures showing overstress features and chipping and flaking of the coating adjacent to the fractures. Many of the blades also contained trailing edge impacts and fractures. The leading edges of all blades had varying amounts of previously molten metal spatter on the surfaces. On blade 4, spattered metal was visible on the leading edge up to the fracture, but not onto the fracture, indicating spatter deposition prior to blade fracturing.

NTSB Probable Cause

Loss of engine power for reasons that could not be determined because postaccident examination of the airframe and engine did not reveal any anomalies that would have precluded normal operation.