Biggs, CA, USA
N3633C
SCHWEIZER AIRCRAFT CORP G 164B
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.
HISTORY OF FLIGHTOn May 13, 2014, at 1320 Pacific daylight time, a Schweizer Aircraft Corporation G-164B Ag Cat, N3633C, impacted terrain shortly after departing from Jones/Ag-Aviation Airport, Biggs, California. CW Equipment Rentals, Inc., owned the airplane and Williams Ag Service, Inc., was operating the airplane under the provisions of 14 Code of Federal Regulations Part 137 as a local aerial application flight. The commercial pilot, the sole occupant, was not injured; the airplane sustained substantial damage. Visual meteorological conditions prevailed and a flight plan had not been filed. According to the operator, the accident flight was to be the pilot's seventh flight of the day in that airplane. The pilot had landed just prior to the accident, and subsequently departed with a full load of seed. During takeoff the engine experienced a loss of power and collided with a berm about 200 feet from the end of the runway. The airplane sustained damage to the firewall during the accident sequence. A Federal Aviation Administration (FAA) inspector examined the airplane after the accident occurred. He stated that there was no visual evidence of a catastrophic mechanical malfunction. The fuel line (hose) from the firewall to the gascolator was disconnected at the gascolator in an effort to drain the remaining fuel from the wing tanks. The fuel tank was free of debris and about 50 gallons of Jet A fuel inside the tank was clean. AIRCRAFT INFORMATIONThe airplane was a Schweizer Aircraft Corporation G-164B Ag Cat, serial number 776B, manufactured in 1986 and purchased by the owner in February 2012. A review of the logbooks revealed that the airframe had undergone an annual inspection on April 03, 2014, at a total time of 10,555.6 hours, equating to about 64 hours prior to the accident. The airplane was powered by a Pratt & Whitney PT6A-34 turboprop engine (serial number 50188) and had accumulated an estimated total time of 10,791.5 hours since manufacture. The last engine overhaul and annual inspection occurred 619.6 and 63.2 hours, respectively, prior to accident. The operator purchased a turbine conversion kit Supplemental Type Certificate (STC) SA1377GL from Turbines Inc., in January 2013 and the engine was repaired and overhauled on March 28, 2013 at a total time of 9,210.3 hours, equating to 9,364 cycles. The airplane's maintenance records indicated that thereafter, the engine was installed on the airframe and returned to service on April 12, 2013. In the 2013 agriculture season the airplane was flown about 170 hours without incident no evidence of mechanical anomalies. The last 100 hour inspection was recorded as being accomplished on July 18, 2013 and the last 400-hour inspection on April 11, 2014 (or about one month prior to the accident). AIRPORT INFORMATIONThe airplane was a Schweizer Aircraft Corporation G-164B Ag Cat, serial number 776B, manufactured in 1986 and purchased by the owner in February 2012. A review of the logbooks revealed that the airframe had undergone an annual inspection on April 03, 2014, at a total time of 10,555.6 hours, equating to about 64 hours prior to the accident. The airplane was powered by a Pratt & Whitney PT6A-34 turboprop engine (serial number 50188) and had accumulated an estimated total time of 10,791.5 hours since manufacture. The last engine overhaul and annual inspection occurred 619.6 and 63.2 hours, respectively, prior to accident. The operator purchased a turbine conversion kit Supplemental Type Certificate (STC) SA1377GL from Turbines Inc., in January 2013 and the engine was repaired and overhauled on March 28, 2013 at a total time of 9,210.3 hours, equating to 9,364 cycles. The airplane's maintenance records indicated that thereafter, the engine was installed on the airframe and returned to service on April 12, 2013. In the 2013 agriculture season the airplane was flown about 170 hours without incident no evidence of mechanical anomalies. The last 100 hour inspection was recorded as being accomplished on July 18, 2013 and the last 400-hour inspection on April 11, 2014 (or about one month prior to the accident). ADDITIONAL INFORMATIONThe assembly instructions in the Parker 111 catalog provided an overview of the assembly and not detailed assembly instructions. This assembly overview was similar to that in Federal Aviation Administration materials (CFR FAR 43.13 and AC 43.13-1b). According to Parker, when assembling a fitting into the hose, friction is created from the interference fit between the hose and the nipple. Oil is required because it reduces that friction to a level acceptable for a compliant assembly. The interference fit is what gives the hose assembly the proper compressive fit between the hose and fittings and provides the proper pressure rating for the hose. When the assembler starts and stops, as when using a wrench and a vise, significant heat can be built up from the induced friction from the continuous starting and stopping motion. Starting and stopping leads to higher friction levels than one continuous motion of assembly. Due to the interference fit, every start and stop also moves the inner tube back and forth. The back and forth motion coupled with an added level of heat due to induced friction 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 inner liner twisting, and can lead to a complete blockage of the hose. To ensure the assembler has not mistakenly compromised the inside of the hose Parker recommends that the hose be inspected and a specific size ball be routed through the hose assembly to ensure there is no blockage or obstruction after the assembly process. This is especially important in hoses where two 90 degree fittings are installed and a visual inspection is not possible without special borescope equipment. The ball test was not stated in the 111 instructions, however AC 43.13-1B shows in TABLE 9-4 the "Ball diameters for testing hose restrictions or kinking," but there is no reference to when or how this should be performed. In the Parker "Aerospace Fabrication Procedure Specification" document AFP501 there are explicit details of the assembly requirements, although this document is not available to the public. With regards to the installation of the nipple into the hose, it stated that the nipple should be inserted with light pressure until the nipple moves into the bore of the hose in an effort to reduce the chance of cutting the inner tube. It additionally stated that after assembly the hose should be checked for cut, damage, or an imperfect hose inner tube. In the troubleshooting portion of AFP501, it stated that if cut rubber is evident inside the hose that this could be caused by the following reasons: -machine chuck and socket vise out of line with one another, causing nipple to enter hose I.D. eccentrically. -hose bottomed tightly against socket shoulder, deforming hose I.D. -sharp edge or burr on nipple pilot. -insufficient lubricant used during nipple assembly. TESTS AND RESEARCHEngine Examination The engine was sent to a repair facility for a teardown examination/repair and the related accessories were sent for functional evaluation. The engine was split at the C flange and the power section of the engine was removed for disassembly. It was noted that the exhaust duct was wrinkled due to impact and that the propeller shaft would not turn indicating the exhaust duct and power turbine was miss-aligned likely as a result of impact. The power section sustained crush damage. The accessory gearbox was found to exhibit corrosion signatures. All fuel related accessories were sent for functional evaluation and no anomalies were found. The engine examination report was reviewed by a representative from Pratt and Whitney. He stated that the there was no signatures indicated the engine had a mechanical malfunction. Fuel Line The drawings for the STC indicated that the fuel hose assembly from the firewall to the gascolator should be modified at installation. The part number indicated the hose required was an Integrated Aircraft 156F001-12D-0210. According to Stratoflex Products Division of Parker Hannifin Corporation, this hose would be a 156-12 (approximately 0.75 inch inside diameter) stainless-braided hose with a firesleeve and 21 inches length with straight fittings on both ends. The hose removed from the airplane was a 111-12 black fabric-hose with no identification markings and had a straight fitting on one and a 90-degree fitting on the other. Overall length was 12.5 inches. The fitting diameter is the same size for both hoses which will deliver a similar flow and pressure. The STC indicated that the life limited parts/fluids service life for "Engine Compartment Fuel Hose or Fuel Lines" was to be "replace at engine overhaul or on condition; maximum life 5 years." The logbooks did not show that the fuel line was replaced after the engine installation. The operator received the newly-overhauled accident engine following the post-accident examination. During the installation and final rigging, the personnel performing the maintenance examined the fuel system in an effort to troubleshoot a fuel leak. Following the removal of the gascolator, the bypass valve appeared to operate normally and engine fuel hoses and lines were examined for proper flow capability. The fuel line from the firewall to the gascolator did not flow as expected and upon removal, maintenance personnel noticed that the hose appeared to be blocked. Compressed air was directed through one end of the hose and a black piece of material ejected out the opposite side. When flattened, the material was about one inch by one inch. The hose and ejected material were sent to the NTSB investigator-in-charge (IIC), and examined at the facilities of Parker Hannifin Corporation/Parker Aerospace. The complete examination report with imbedded pictures detailing the findings is contained in the public docket of the accident. The hose was constructed of a 90-degree fitting on the end connecting into the firewall and a straight-fitting connecting into the gascolator. From the pictures, it was apparent that the firesleeve was not equipped with hose clamps. The firesleeve did not have band clamps and there was no identification tag. The insides of the firesleeve were different on both ends: the straight-fitting end was white and fluffy, where the 90-degree side was matted and hard with a redish/orange coloration. Parker representatives stated this signature was indicative of the straight-fitting end not being dipped (a process in which the firesleeve is dipped in a high-temperature RTV silicone). This is consistent with reusing a firesleeve from another hose and cutting one end to resize it to the new hose without redipping it. The internal examination of the hose assembly was done by utilizing a borescope. There were notable flaps of loose hose where the end of the 90-degree nipple rested against the inter hose walls. A piece of a flap was taken for material analysis to compare it to the larger ejected-flap material. They were similar in composition consistent with the ejected flap originating from the inside of the hose. The inter diameter (ID) of the hose was about 0.60 inches and the outer diameter (OD) of the nipple was 0.66 inches and its ID was 0.57 inches.
The assembler’s improper fabrication of a fuel line (hose) and the subsequent failure to verify that it was not occluded, which resulted in fuel starvation and a total loss of engine power during takeoff.
Source: NTSB Aviation Accident Database
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