N3633CSchweizer Aircraft G-164B

On 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.

The 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).

The 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).

The 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.

Engine 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.

On May 21, 2010, about 1600 Pacific daylight time (PDT), a Schweizer G-164B AgCat, N3633C, during landing with a suspected brake problem, the airplane veered off the runway and came to rest in an irrigation ditch near Robbins, California. Sunrise Dusters, Inc., was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 137. The certificated commercial pilot sustained serious injuries; the airplane sustained substantial damage to the left and right wing spars. The local agricultural aerial application flight departed Robbins about 1530. Visual meteorological conditions prevailed, and no flight plan had been filed.

The pilot reported that during the flight he noticed that the right brake pedal was stiff. He saw what appeared to be hydraulic fluid leaking on his foot from what he thought might be from the parking brake valve. The pilot tried without success to set and release the brake to correct the stiff brake pedal. He radioed in to his base of operations; he notified ground personnel of the possible brake problems, and his intentions to return to the airfield.

During the landing, as the right wheel touched down the airplane pulled to the right; the pilot attempted to bring the airplane back towards the left. During the correction, the pilot felt the wind shift. The airplane veered back towards the left, departed the runway, and came to rest in an irrigation ditch.

The airplane sustained substantial damage to both the right and left wing spars. The propeller was substantially damaged, and a large quantity of soil entered the engine intake. The left and right main landing gear struts were damaged when the aircraft went into the ditch. The right brake calipers separated from the airplane, and were found within a few feet of the initial touchdown point of the right main landing gear tire.

The airplane was recovered from the ditch, and moved to the company’s hangar for further examination.

The Federal Aviation Administration (FAA) accident coordinator examined the airplane and the accident site.

The right wheel was found to have the entire inboard flange separated from the inboard wheel half. The tire was a tube type and the tube was still inflated. The tire expanded beyond where the flange once was and pushed the broken wheel flange pieces into the brake disc assembly. The tire was deflated and the parts were retained for examination.

The attach points of the brake disc were found to be bulged and stressed. The attach points of the disc are normally located on the wheel assembly inner diameter. The force of the inflated tire and tube pushed inward radially against the brake disc with great force. The FAA inspector opined that the wheel flange failed in-flight, and gave the pilot a locked brake pedal feel.

The installed tire on the accident airplane was 29x11.0-10. The manufacturer of the wheel assembly for the Ag-Cat G-164B (Part number 40-101) reported that the proper tire size should be 8.50-10.

The FAA accident coordinator contacted the type certificate holder of the Ag-Cat G-164B and was advised that some operators of the accident airplane model have obtained a field approval to use oversize tires from their local FAA Flight Standard District Office.

As a result of this accident and the subsequent investigation, the FAA issued a Special Airworthiness Information Bulletin SAIB CE-11-06 on December 15, 2010, making recommendations to operators who may be operating oversized tires. The SAIB made the following recommendations:

“All operators of 14 CFR part 21, section 21.25 Restricted Category and 14 CFR part 23 Normal Category certificated airplanes that are currently operating with or may modify their aircraft to operate with oversized tires different from the aircraft’s approved type design, should acquire an STC or field approval supported by FAA-approved data with similar original equipment manufacturer (OEM) restrictions for installation, pressure, etc. before doing so. The approved data should include flight test requirements and their results as well as system design and structural analysis. Guidance for replacing OEM tires with oversized tundra tires is provided in FAA Advisory Circular (AC) AC 23-17B. The AC summarizes the results of flight tests recommended by the National Transportation Safety Board, and conducted by the FAA for evaluation of tundra tires installed on a Piper PA-18. In addition, the AC provides information of these tires as well as testing of their installation. Although the guidance in the AC is based specifically on the Piper Aircraft, Inc. PA-18, it identifies issues and guidance that can be extended to other airplane types equipped with oversized tires. The AC also identifies the possible performance effects and flight and ground handling characteristics that may be altered with the installation of the tundra tires. Potential propulsion system effects such as unusable fuel may be affected by changes in normal flying attitude. Review of all these potential effects as identified in AC 23-17B should be evaluated.

Before installation of larger tires operators should do the following as a minimum:

1.

Initially inspect wheels for cracks using an industry standard fluorescent penetrate process with annual inspections thereafter.

Install only approved vendor supplied tires.

Install new tubes.

Determine the appropriate tire pressure for the specific tire, aircraft, and aircraft operations in consultation with the approved tire manufacturer and FAA Advisory Circular, AC 23-17B.

Check for clearance between the tire and brake components.

Check the tire pressure and abnormal wear at 2 week intervals or less.

Additional safety information to the public of potential problems associated with aircraft with oversized tires is also provided in Safety Alert for Operations (SAFO) 10007, dated 5/24/10. The SAFO provides recommended actions for persons interested in operating aircraft with oversized tundra tires as well as with skis, or wheel/ski installations.

Owners and operators of Restricted Category and Normal Category airplanes who intend to modify their aircraft with oversized tires should review the above documents for guidance and the issues to consider and evaluate when replacing the manufacturer’s recommended main landing gear wheels and/or tires with oversized replacements.”