ERA10FA409

The manufacturer's inadequate quality control and improper manufacture of the fuel servo diaphragm assembly, which resulted in fatigue cracking of the hub stud and subsequent loss of engine power due to fuel starvation.

During the cruise portion of a positioning flight, the pilot reported a loss of engine power to air traffic controllers. He was then radar vectored towards the closest airport but was unable to reach it. The airplane impacted trees, was partially consumed by a postimpact fire, and the pilot was fatally injured. Examination of the engine's fuel servo revealed that the hub stud in the fuel servo diaphragm assembly was fractured, which would have resulted in the fuel servo being unable to properly meter fuel. Review of maintenance records revealed that an engine overhaul had been completed approximately 18 hours prior to the accident and that the fuel servo was shipped to the fuel servo manufacturer, where the unit was overhauled using the manufacturer's components. Examination of the hub stud revealed that it fractured as a result of fatigue cracking. The most likely cause of the fatigue cracking was a lack of braze material, which should have filled the gap between the hub stud and the hub and would have supported the shoulder of the hub stud. The manufacturer's brazing process documentation indicated that a visual check would have been performed to ensure that the braze did not exceed a certain measurement over the hub or hub stud, but there was no specific indication that a check would have been made to ensure that the braze was visible at the joint edges as required by the braze process specification, nor did any of the records provided by the manufacturer indicate the quantity of braze to be used for each assembly or how it was applied. The hub stud from the airplane and a hub stud from an exemplar assembly (from the same batch) were also found to be significantly softer than specified by the manufacturer's assembly drawing. Based on the hardness measurements, the ultimate tensile strengths of these hub studs was only about 80 percent of the expected tensile strength. Fatigue resistance of the hub stud would have correlated with the tensile strength, so the reduced hardness relative to the specification likely played some role in the rapid onset and propagation of the fatigue cracking. The reduced hardness of the hub studs indicated that the thermal history for the brazing process was either incorrectly specified or that the process was not properly controlled for this lot of assemblies. Also indicative of the manufacturer’s poor quality control was the lack of conformance to the drawings for the hub stud from the airplane and the exemplar hub studs; these hub studs had a groove perpendicular to the axis of the stud at the termination of the threads on the hub end, which was not in the drawing, and may have increased the stress concentrations. The hub stud from the accident fractured at the midplane of this groove, at the plane of maximum stress concentration.

HISTORY OF FLIGHT On August 10, 2010, about 0215 eastern daylight time, a Piper PA-32R-301, N220ST, operated by Coastal Aviation, was substantially damaged when it impacted trees while making a forced landing following a loss of engine power during cruise flight near Washington, Georgia. The certificated commercial pilot was fatally injured. Visual meteorological conditions (VMC) prevailed for the flight that departed Madison County Executive Airport (MDQ), Huntsville, Alabama, destined for Mt. Pleasant Regional Airport (LRO), Mount Pleasant, South Carolina. An instrument flight rules (IFR) flight plan was filed for the positioning flight conducted under 14 Code of Federal Regulations (CFR) Part 91. On the morning of August 9, 2010 after receiving a call from a freight forwarding company, the operator's general manager (who was also the accident pilot) flew the accident airplane to Charleston International Airport (CHS), Charleston, South Carolina to conduct a 14 CFR Part 135 air taxi flight. After loading approximately 400 pounds of freight, at approximately 1207 the pilot departed for MDQ. After arriving at 1414, and off-loading the freight, the pilot attempted to depart; but, the airplane would not start. After a mechanic replaced the starter, the pilot departed MDQ for LRO the following morning at 0048. According to air traffic control (ATC) information provided by the Federal Aviation Administration (FAA), during cruise flight at 7,000 feet above mean sea level, the pilot reported a loss of engine power. He was then radar vectored by ATC towards the closest airport which was Washington-Wilkes County Airport (IIY), Washington, Georgia. ATC continued to monitor the airplanes flight path as it descended. Approximately 3 nautical miles southeast of IIY, radar contact was lost as the airplane descended below the radar coverage area. PERSONNEL INFORMATION According to FAA records, the pilot held a commercial pilot certificate with multiple ratings including airplane single-engine land, and instrument airplane. His most recent FAA second-class medical certificate was issued on June 30, 2010. On that date, he reported that he had accrued 2,600 total hours of flight experience. The pilot had at one time been listed in the operator's FAA approved Part 135 operations specifications when the operator had been operating Part 135 with multiple pilots. According to the FAA, at the time of the accident however, the operator was only authorized to operate its Part 135 flights with one pilot. The pilot of the accident airplane was not that authorized individual. AIRCRAFT INFORMATION The accident aircraft was a low wing, unpressurized, six seat, single-engine monoplane of conventional stressed skin construction. It was powered by a 300 horsepower, Lycoming IO-540-K1G5 fuel injected engine, equipped with a Hartzell HC-13YR-1, controllable pitch, 3- bladed propeller. According to FAA and airplane maintenance records, the accident airplane was manufactured in 2004. An engine overhaul had been completed on July 22, 2010. At the time of accident, the engine had accrued 18 hours since the overhaul had been completed. The airplane’s most recent annual inspection was completed on July 30, 2010, and at the time of the inspection, the airplane had accrued 1959.5 total hours of operation. METEOROLOGICAL INFORMATION The recorded weather at Greene County Airport (3J7), Greensboro, Georgia, approximately 19 nautical miles southwest of the accident site, at 0220, included: wind 100 degrees at 3 knots, visibility 10 miles, sky clear, temperature 26 degrees C, dew point 21 degrees C, and an altimeter setting of 29.99 inches of mercury. WRECKAGE AND IMPACT INFORMATION The wreckage was located in a heavily wooded area approximately 1.6 miles southeast of IIY. All major components of the airplane were located at the accident site. After impacting trees, the airplane came to rest inverted on a magnetic heading of 350 degrees. A 100-foot long debris field, oriented on a magnetic heading of 302 degrees was present. Multiple portions of broken tree limbs were spread throughout the area. Evidence of a flash fire was present, and the majority of the cabin area had been consumed by a post crash fire. Both the landing gear and the flaps were in the retracted position. Both fuel caps were found to be closed and locked. The fuel selector valve was in the right tank position and the valve contained approximately a teaspoon of fuel. The mixture control was in the idle cutoff position. Both wings were fragmented into multiple pieces, exhibited fracturing and various degrees of crush damage. The wing flaps and ailerons exhibited multiple breaks and separations and were spread throughout the debris field. The empennage was separated from the remains of the aft fuselage. The rudder panel remained attached to its fittings on the vertical stabilizer and the left and right portions of the stabilator exhibited fracturing and crush damage. The pitch trim jackscrew was found in the full nose-up position, however; no preimpact failures or disconnects of the primary flight control system were discovered and control continuity was established from the ailerons, stabilator, and rudder to the broken ends of the control cables, which exhibited evidence of tensile overload. Examination of the 3-bladed constant speed propeller revealed that there was no evidence that it had been rotating when the accident occurred. One blade was bent back approximately 90 degrees at the mid span position, one blade was straight, and the third blade exhibited slight aft bending toward the tip. Further examination also revealed that the propeller governor was in the high pitch position. Examination of the engine revealed that there was no evidence of any blockage of the intake system or exhaust system, the crankshaft could be rotated, and continuity of the valve train, and crankshaft were confirmed. All of the spark plugs electrodes were intact and light gray in color, and thumb compression was noted on all six cylinders. All six cylinders were also examined internally with a lighted borescope, and no anomalies were observed. Both magnetos were fire damaged, but exhibited no internal or external evidence of any preimpact malfunction. The oil suction and oil pressure screens were absent of debris, and oil was noted in the rocker boxes. External examination of the fuel injection system revealed no indication of any preimpact failure or malfunction of the fuel nozzles or fuel flow divider. However, during internal examination of the fuel servo, it was discovered that the stud which attached to the hub in the diaphragm assembly was fractured. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was performed on the pilot by the Georgia Bureau of Investigation's Division of Forensic Sciences. The cause of death was smoke, soot, and super-heated gas inhalation and multiple blunt force injuries. Toxicological testing of the pilot was conducted at the FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma. The specimens were negative for carbon monoxide, cyanide, basic, acidic, and neutral drugs. TESTS AND RESEARCH Fuel Servo According to airplane maintenance records during the engine overhaul which was completed on July 22, 2010, the fuel servo was shipped to AVStar Fuel Systems Inc. where the unit was overhauled using AVStar components in accordance with FAA approved data from the manufacturer's Component Maintenance Manual. According to the engine manufacturer, the fuel injection system was a mass-air flow type fuel injection system. The fuel servo as part of that system would sense the amount of air moving past the throttle by use of a venturi. A diaphragm in the fuel servo would meter the amount of fuel supplied to the flow divider by comparing the air pressure from the venturi. The flow divider would then divide the metere