History of Flight
On May 13, 2014, at 1320 Pacific daylight time, a Schweizer Aircraft Corporation G-164B Ag Cat, registration N3633C, impacted terrain shortly after departing from Jones/Ag-Aviation Airport in Biggs, California. The aircraft was owned by CW Equipment Rentals, Inc. and operated by Williams Ag Service, Inc. under 14 CFR Part 137 for a local aerial application flight. The commercial pilot, the sole occupant, was not injured, but the airplane sustained substantial damage. Visual meteorological conditions prevailed, and no flight plan was filed.
According to the operator, the accident flight was the pilot's seventh of the day in that airplane. After landing just prior, the pilot departed with a full load of seed. During takeoff, the engine experienced a loss of power, and the airplane collided with a berm about 200 feet from the end of the runway. The firewall was damaged during the accident sequence.
Aircraft Information
The airplane, a Schweizer Aircraft Corporation G-164B Ag Cat (serial number 776B), was manufactured in 1986 and purchased by the owner in February 2012. Logbooks showed the airframe underwent an annual inspection on April 3, 2014, at a total time of 10,555.6 hours, approximately 64 hours before the accident. The Pratt & Whitney PT6A-34 turboprop engine (serial number 50188) had an estimated total time of 10,791.5 hours. The last engine overhaul occurred 619.6 hours prior, and the last annual inspection was 63.2 hours prior.
The operator purchased a turbine conversion kit STC SA1377GL from Turbines Inc. in January 2013. The engine was repaired and overhauled on March 28, 2013, at 9,210.3 hours and 9,364 cycles, and installed on the airframe on April 12, 2013. During the 2013 agriculture season, the airplane flew about 170 hours without incident or mechanical anomalies. The last 100-hour inspection was on July 18, 2013, and the last 400-hour inspection on April 11, 2014.
Additional Information
The fuel line from the firewall to the gascolator was examined. The STC required a hose assembly modification, specifying part number Integrated Aircraft 156F001-12D-0210 (a 21-inch stainless-braided hose with firesleeve and straight fittings). However, the hose removed from the airplane was a 12.5-inch black fabric hose with no markings, having a straight fitting on one end and a 90-degree fitting on the other. The firesleeve lacked band clamps and identification tags; its straight-fitting end showed evidence of not being dipped in RTV silicone, consistent with reuse and resizing from another hose.
Parker Hannifin representatives explained that proper assembly of hose fittings requires lubricant to reduce friction; starting and stopping during assembly can increase friction, potentially damaging the inner tube. They recommended a ball test to verify no blockage, but this was not in the 111 instructions.
Tests and Research
After the accident, the engine was sent to a repair facility for teardown examination. The exhaust duct was wrinkled, and the propeller shaft would not turn, likely from impact. The power section had crush damage; the accessory gearbox showed corrosion. Fuel accessories functioned normally, and Pratt & Whitney stated no signs of mechanical malfunction.
During reinstallation of the overhauled engine, maintenance personnel found the fuel line from the firewall to the gascolator appeared blocked. Compressed air expelled a black piece of material about one inch by one inch. The hose and material were sent to Parker Hannifin for examination. Borescope inspection revealed loose flaps inside the hose near the 90-degree fitting nipple. Material analysis confirmed the flaps were consistent with the ejected material, indicating blockage originated from inner hose degradation. The inner diameter of the hose was approximately 0.60 inches, while the outer diameter of the nipple was 0.66 inches and its inner diameter 0.57 inches.