WPR14LA201 · Schweizer Aircraft Corp G 164B B

The commercial pilot departed for his seventh agricultural application flight of the day with a full load of seed on board. The operator reported that, during takeoff, the engine experienced a loss of power and subsequently collided with a berm near the end of the runway. A postaccident examination of the engine and fuel-related accessories revealed no evidence of a mechanical malfunction or failure.

The operator had purchased a turbine conversion kit supplemental type certificate about 1 year before the accident. The engine was overhauled and reinstalled on the airplane, which was subsequently flown about 170 hours without incident. Postaccident examination of the engine revealed that, during the conversion, maintenance personnel installed a fuel line (hose) from the firewall to the gascolator that was different from that shown in the engineering drawings. The installed hose was shorter and had a 90-degree fitting on one side and a straight fitting on the other rather than straight fittings on both ends. The hose was occluded by a piece of the hose's inner lining. Compressed air was directed through one end of the hose and a black piece of material ejected out the opposite side. An internal examination of the hose assembly revealed that there were flaps of loose hose where the end of the 90-degree fitting rested against the interhose walls. The flap material and the ejected piece of material both matched the material of the interhose; these materials likely completely blocked the hose, which resulted in fuel starvation to the engine.

A representative from the hose manufacturer stated that, when the hose assembler starts and stops the installation of the nipple into the hose, significant heat can build up from the induced friction caused by the continuous starting and stopping motion; this can break down the binding that holds the inner tube to the outer layers of the hose and may result in the nipple digging into the inside diameter of the hose liner. In extreme cases, this can result in the inner liner twisting and lead to a complete blockage of the hose, which is likely what occurred to the accident hose. The representative further stated that, after the hose assembly process, the assembler should route a specific-sized ball through the hose assembly to ensure there is no blockage or obstruction. However, the manufacturer's hose assembly instructions did not provide detailed instructions on the assembly process or recommend how to verify that the hose was not occluded during assembly.

Verbatim NTSB analysis and probable cause from the NTSB dataset