Tampa, FL, USA
N5307A
CESSNA 210N
As the on-demand air cargo flight approached the destination airport, the pilot advised air traffic control that the airplane's engine had "lost oil pressure." Subsequently, an air traffic controller cleared the flight to land on an alternate runway. The airplane impacted a berm short of the runway threshold, which resulted in serious injury to the pilot and substantial damage to the airframe. Postaccident examination of the wreckage revealed that engine oil was present from the windscreen to the vertical stabilizer and that the engine case had been breached near the Nos. 4 and 6 cylinders. Detailed examination of the engine revealed signatures consistent with oil starvation and a fatigue failure of the No. 4 connecting rod and connecting rod cap. Although the metallurgical hardness of one of the No. 4 connecting rod bolts was slightly below its specified value, this likely did not contribute to its separation, and it likely failed in overstress after the fatigue-related separation of the mating connecting rod. The engine's oil sump was breached and only contained residual traces of engine oil; the preaccident quantity of oil within the engine could not be determined. Examination of the engine's oil galleys and passages revealed that they were intact, clear, and unrestricted. The root cause for the loss of lubrication and subsequent fatigue failure of the No. 4 connecting rod could not be determined.
On December 19, 2013, at 2351 eastern standard time, a Cessna 210N, N5307A, was substantially damaged during a forced landing following a total loss of engine power while on approach to Tampa International Airport (TPA), Tampa, Florida. The commercial pilot was seriously injured. Visual meteorological conditions prevailed and the airplane was operating on an instrument flight rules flight plan. The flight had originated from Valdosta Regional Airport (VLD), about 2307, and was destined for TPA. The on-demand air cargo flight was conducted under the provisions of Title 14 Code of Federal Regulations (CFR) Part 135.According to air traffic control (ATC) radar and voice communication information provided by the Federal Aviation Administration (FAA), the pilot was cleared to land on runway 1R at 2345 while approaching TPA. At 2346, the pilot advised ATC that he needed to land on runway 10, and that the airplane's engine had "lost oil pressure." ATC then advised the pilot that runway 10 was closed for construction and that he could immediately turn left for a landing on runway 19R. At 2347, ATC asked the pilot if he required any emergency equipment, to which the pilot replied in the negative and stated that the engine was "running a little rough here, I should be able to make it though." About 30 seconds later the pilot revised his request and asked ATC to provide emergency response equipment for his landing. No further transmissions were received from the pilot. A helicopter operated by the Tampa Police Department observed the airplane as it approached and impacted a berm short of runway 19R, on the airport property. The helicopter then landed adjacent to the accident site, and one of the crewmembers successfully extracted the pilot from the wreckage. The pilot held a commercial pilot certificate with ratings for airplane single and multi-engine land, as well as instrument airplane. The operator reported that he had accumulated 6,912 total hours of flight experience, 412 hours of which were in the accident airplane make and model. The pilot's most recent CFR 135 proficiency check was completed on a flight immediately preceding the accident flight. According to FAA airworthiness records, the airplane was manufactured in 1979. It was equipped with a Continental Motors IO-520-L reciprocating engine rated at 285 hp. The engine was installed onto the airframe following a rebuild by Continental Motors on December 18, 2009. The airplane's most recent 100-hour inspection was completed on November 26, 2013. At that time, the number 1 cylinder was removed to replace a broken exhaust valve, and the exhaust valve seats of cylinders number 1, 2, and 3 were lapped. Additionally, the engine oil filter was changed and the element of the old filter was examined, the oil was drained, and the engine was subsequently serviced with 11 quarts of oil. At the time of the 100-hour inspection, the engine had accumulated 1,579 total hours of operation since it had been installed in 2009. The maintenance logs did not detail any further maintenance of the engine, and at the time of the accident, the airplane had accumulated 41 additional flight hours since the 100-hour inspection. Review of the operator's operations specifications showed that the engine model's overhaul time-in-service interval was 1,700 hours. The airframe was examined at the accident site under the supervision of an FAA inspector. Examination of the airframe revealed that the left wing tip was damaged, along with the engine and lower portion of the forward fuselage, which displayed considerable compression-type damage. Engine oil residue was observed on the fractured windscreen and the vertical stabilizer. Flight control continuity was established from the cockpit to all flight control surfaces. The extension of the elevator trim actuator was measured and correlated to a 10-degree tab trailing edge down position. The flaps were found in a position between 0 and 10 degrees of extension, and the flap switch handle was found in the 20-degree position. An unquantified volume of fuel was found in both fuel tanks, and the cockpit fuel selector valve was positioned to the left fuel tank. The fuel boost pump switch was found selected to the "ON" position. The landing gear position selector handle was found set to the "DOWN" position, and the main landing gear was down and locked. The nose landing gear had separated from the fuselage during the impact sequence. The engine remained attached to the fuselage, and the top of the engine crankcase was breached in the vicinity of the number 2 and 4 cylinders. The piston pin and connecting rod of the number 4 cylinder was recovered from inside the engine cowling. The engine was subsequently separated from the airframe and forwarded to its manufacturer for detailed examination. The throttle and fuel metering assembly displayed impact damage signatures to the throttle body. All of the control arms were secured and were capable of movement by hand. The finger screen was absent of contamination. The fuel pump was free to rotate and the fuel pump drive was intact and undamaged. Flow testing of the fuel pump showed that it functioned properly through its full range of operation. The manifold valve plunger assembly was intact, secure and undamaged, and there were no signatures of fuel stains or leakage in the vent chamber side of the diaphragm. The number 2 fuel injector displayed impact damage signatures and a portion of the injector remained in the cylinder, while the number 6 fuel injector was clogged with debris. The numbers 1, 3, 5, and 4 fuel injectors were absent of debris and displayed normal operating signatures. The number 4 spark plugs were oil-soaked and displayed normal wear signatures, while the remaining top and bottom sparkplugs exhibited normal wear signatures. The left and right magnetos turned freely with impulse coupling engagement, and when tested on a test bench with replacement ignition harnesses, produced a blue spark from each lead across a 7 mm gap through the full range of test bench RPM. The oil pump drive was intact. The oil pump cavity contained scoring and scratches consistent with hard particle passage, and small metallic particulates were observed within the oil pump cavity. The oil pump gear teeth were intact and undamaged. The oil pressure relief valve and seat contained small metallic particles, and the seat displayed normal seating signatures. The oil filter element was examined and contained an abundance of flakes and slivers from the damaged internal engine components. The oil sump displayed impact damage signatures, was breached, and only a small amount of residual oil remained within the sump. A significant quantity of metallic debris, consistent with connecting rod, connecting rod bearing, piston, and piston ring material, was observed within the oil sump. Metallic material was observed on the oil suction screen, though the screen was not obstructed. Each of the cylinder combustion chambers had a normal amount of combustion deposits and their bores were free of scoring and undamaged. Each of the intake and exhaust valve heads exhibited normal deposits and operating signatures, and the rocker box area had an oil residue consistent with lubrication to the respective overheads. With the exception of the number 3 cylinder, the remaining overhead components (valves, rocker arms, guides, springs, retainers and shafts) were lubricated and undamaged. The number 3 cylinder intake push rod tube was pushed up into the cylinder overhead, and the push tube washers were deformed. The number 3 intake and exhaust rocker arms were removed and visually inspected; both rocker arms, as well as the remaining intake and exhaust rocker arm shafts, displayed normal operating signatures. Each of the piston heads exhibited normal amounts of combustion deposits and all of their piston skirts displayed some degree of mechanical damage, with the exception of the number 5 and 6 pistons, which were free of damage. A crescent-shaped impression was noted on the number 3 piston face, which was consistent in shape with the outside diameter of the exhaust valve. All of the piston rings were intact, free in their grooves, and exhibited normal wear and operating signatures with the following exceptions: the number 1 bottom piston ring displayed mechanical damage and a portion of the ring was missing; a portion of the number 2 bottom piston ring groove was missing, but the piston ring remained in its normal installation location; the number 3 bottom piston ring displayed mechanical damage and a portion of the ring was missing; portions of the number 4 oil scraper ring were found in the oil sump. Each of the piston pin and plug assemblies were intact and undamaged. The crankshaft and counterweight assembly exhibited lubrication distress, thermal damage, and mechanical damage concentrated at the number 1, 2, 4, and 5 connecting rod journals. The crankshaft main bearing journals were intact, undamaged and exhibited incipient oil starvation signatures. The number 1 connecting rod journal exhibited thermal distress and scoring consistent with deficient lubrication. The number 2 connecting rod journal exhibited signs of lubrication distress, thermal discoloration, mechanical damage and displacement of the journal material. Portions of the number 2 connecting rod bearing were smeared into the journal. The number 3 connecting rod journal was relatively undamaged and showed signs of lubrication. The number 4 connecting rod sustained thermal discoloration, mechanical damage and displacement of the journal material; all consistent with lubrication distress. The number 5 connecting rod journal exhibited thermal distress and scoring from lack of sufficient lubrication. The number 6 connecting rod journal sustained thermal discoloration. Excluding the displacement of journal material on number 2 and 4, the oil transfer passages were open and unrestricted. The oil transfer collar was intact and undamaged. The oil transfer plug was tight and in position. The crankshaft cluster gear was intact and exhibited normal operating signatures. The gear bolts were tight and safety-wired and the gear teeth were undamaged. Each of the five crankshaft main bearings were intact and exhibited evidence of contamination and hard particle passage, with contamination imbedded in the surface layer, and each exhibited incipient signs of lubrication distress. The number 1 connecting rod was intact but exhibited thermal discoloration. Mechanical damage was noted on the connecting rod cap. The connecting rod nuts and bolts were intact and secure. The connecting rod bushing was in place and intact. Only fragments and the connecting rod bearing remained in the bearing support. These fragments of the bearing steel backing displayed evidence of insufficient lubrication and subsequent thermal distress. The number 2 connecting rod exhibited extreme thermal and mechanical damage and was fractured through at the base of the I-beam, separating both sections of bearing supports. Fragments of the connecting rod cap exhibited thermal and mechanical damage. One of the connecting rod bolts remained intact, but was distorted. The other connecting rod bolt and nut were fractured through and exhibited mechanical damage and overload signatures. The connecting rod bushing was in place and intact. Only fragments and the connecting rod bearing remained. These fragments of the bearing exhibited lubrication and thermal distress and were found in the oil sump. The number 3 connecting rod assembly was intact and undamaged. The connecting rod nuts and bolts were intact and secure. The connecting rod bushing was in place and intact. The connecting rod bearing exhibited lubrication distress and thermal smearing of the surface babbit, exposing the copper layer. The number 4 connecting rod exhibited extreme thermal and mechanical damage and was fractured through at the base of the I-beam, separating both sections of bearing supports. Fragments of connecting rod cap exhibited thermal and mechanical damage. Fragments of connecting rod bolts and nuts were fractured through and exhibited mechanical damage and overload signatures. The connecting rod bushing was in place and intact. Only fragments of the connecting rod bearing remained. These fragments of the bearing exhibited lubrication and thermal distress and were found in the oil sump. The number 5 connecting rod was intact but exhibited significant thermal discoloration. The connecting rod nuts and bolts were intact and secure. The connecting rod bushing was in place and intact. The connecting rod bearing exhibited lubrication distress and thermal smearing. Portions of the bearing were extruded out around the sides of the connecting rod. The number 6 connecting rod assembly was intact and undamaged. The connecting rod nuts and bolts were intact and secure. The connecting rod bushing exhibited normal operating and lubrication signatures. The connecting rod bearing exhibited lubrication distress and thermal smearing of the surface babbit, exposing the copper layer. The camshaft lobes exhibited normal operating signatures and mechanical damage from contact with metallic debris. The camshaft cluster gear was intact and exhibited normal operating signatures. The gear bolts were tight and safety-wired, and the gear teeth were undamaged. Two holes were observed on the topside of the left crankcase halves; one above the number 2 cylinder bay and the other above and adjoining the number 4 cylinder bay. Internally, mechanical damage was observed on the front ends of the cylinder bays 1, 2, and 3 and on all sides of the number 4 cylinder bay. The main bearing support mating surfaces were intact and exhibited no signs of fretting. The main bearing support diameters were intact and exhibited no signs of bearing movement, rotation, or bearing tang lock-slot elongation. The oil galleys and passages in the left and right crankcase halves were intact, clear, and unrestricted. The propeller governor shaft could not be rotated by hand and was disassembled. Internal examination of the components revealed evidence of hard particle passage on the pump gears and pump walls. The number 4 connecting rod, connecting rod cap, and connecting rod bolts were submitted to the NTSB Materials Laboratory for detailed examination. The connecting rod had fractured into three pieces, while the connecting rod cap had fractured into two pieces. A section of the connecting rod cap was missing. Each of the bolts had fractured into two pieces, with the head ends wedged inside the mating connecting rod pieces and the threaded ends loose. A nut was still assembled onto the threaded end of one of the bolts, while the remaining nut was not recovered. Overall examination revealed that most of the pieces had post-fracture damage that obscured the fracture surface features, with the exception of one cap piece and the threaded ends of the bolts. All of the fracture surfaces were examined in detail using a 5 to 50X stereo-zoom microscope. The un-obscured fracture surface of the connecting rod cap piece was relatively flat with multiple thumbnail-shaped patterns that were consistent with fatigue. The fatigue crack thumbnails emanated from the inner and outer surfaces of the cap, and numerous ratchet marks were observed perpendicular to the inner and outer surfaces. The features were consistent with fatigue initiating from the inner and outer surfaces of the cap and propagating inward. The fracture surface was comprised of 57% fatigue cracking initiating from the inner surface, 21% fatigue cracking initiating from the outer surface, and the remainder consistent with overstress. Stereomicroscopic examination of the threaded ends of the bolts revealed necking of the shank of the bolts adjacent to the fracture surfaces. The features on the bolt fracture surfaces were rough and grainy, and were surrounded by shear lips. The necking, rough fracture surfaces, and shear lips were consistent with overstress failure. Representative connecting rod, cap, and bolt pieces were analyzed using a Thermo Scientific Niton XL3t-980 x-ray fluorescence (XRF) alloy analyzer. The alloy analyzer identified the materia
A total loss of engine power due to the fatigue failure of the No. 4 connecting rod. Contributing to the accident was a likely loss of lubrication for reasons that could not be determined during a postaccident engine examination.
Source: NTSB Aviation Accident Database
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