Phoenix, AZ, USA
N671VC
BEECH N35
The airplane was over mountainous terrain when the pilot noticed the engine oil pressure was below 30 psi. He determined that the closest suitable airport was his destination airport, and continued to that airport. Shortly thereafter, the engine oil pressure dropped to zero, and the engine began to shake violently. The pilot shut down the engine, declared an emergency, and turned towards the nearest airport displayed on his GPS, but he did not have enough altitude to glide all the way to the airport. The pilot executed a forced landing in desert terrain. During the landing, the airplane sustained substantial damage to the nose and left wing. Postlanding photographs show oil and dirt streaks along the right side of the airplane originating from the vicinity of the engine cowling. A postaccident engine examination revealed that the lower bolts that secured the engine oil cooler were not tight and that the lower half of the oil cooler gasket was deformed, which allowed pressurized oil to exit the engine along the bottom of the oil cooler adaptor plate. Additional engine cooling baffling was also secured to the engine by the oil cooler bolts. Thermal and mechanical damage within the engine was consistent with oil starvation. The airplane had its annual inspection 6.4 hours prior to the accident. A normal part of the annual inspection would have been to remove the baffling around the engine oil cooler in order to fully access the engine; the baffling would be replaced after completion of the inspection. It is likely that the bottom bolts of the engine oil cooler where the baffling attached were not properly torqued during reinstallation.
HISTORY OF FLIGHTOn October 18, 2012, at 1040 mountain standard time, a Hawker Beechcraft N35, N671VC, experienced a loss of engine power while en route to Phoenix Deer Valley Airport, Phoenix, Arizona. The pilot conducted a forced landing 10 miles northwest of Deer Valley Airport in desert terrain. The airplane was registered to the private pilot who operated it under the provisions of Title 14 Code of Federal Regulations, Part 91. The pilot was not injured, and the airplane was substantially damaged. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight originated from Prescott, Arizona, at 1009. The pilot reported that he had just made contact with Phoenix Approach Control, and was over mountainous terrain when he noticed the engine oil pressure was below 30 psi. He determined that the closest suitable airport was his destination airport, Deer Valley, and continued to that airport. Shortly thereafter, the engine oil pressure dropped to zero, and the engine began to shake violently. He shut down the engine, declared an emergency, and pushed the 'nearest' button on the GPS, which indicated Pleasant Valley Airport as the closest airport. He turned towards Pleasant Valley Airport, but he did not have enough altitude to glide all the way to the airport. The pilot executed a forced landing in desert terrain about 2.8 miles east of the Pleasant Valley Airport. During the landing, the airplane sustained substantial damage to the nose and left wing. Post landing photos show oil and dirt streaks along the right side of the airplane emanating from the engine cowling. PERSONNEL INFORMATIONThe pilot, age 69, held a private pilot certificate with ratings for airplane single-engine land and instrument airplane issued March 11, 2006, and a third-class airman medical certificate issued September 29, 2011, with the limitation that he wear corrective lenses. The pilot reported that he had 4,782 total flight hours, 2,403 hours in the accident airplane make and model, and had accumulated 24 hours in the last 90 days, and 7 hours in the 30 days prior to the accident. AIRCRAFT INFORMATIONThe four-seat, low-wing, retractable landing gear airplane, serial number D6732, was manufactured in 1961. It was powered by a Continental Motors IO-470-HcN10B 260-hp engine, and equipped with a McCauley constant speed propeller, model number 2A36C23-P-F-G/S84B-0. Review of copies of the airframe log book showed an annual inspection was performed on September 12, 2012, at a total airframe time of 4,760.50 hours (1,063.80 tach). The engine log book showed an annual inspection completed on September 12, 2012, at a total engine time of 3,744.0 hours, and 1,345.4 hour since major overhaul (SMOH). The hours indicated on the tach as recorded during the post-accident examination was 1,070.21. The tach time between the annual inspection and the accident was 6.41 hours. A review of the airplane's FAA Airworthiness documentation shows that an airframe modification was installed on November 7, 2002, which places cooling air baffles around the oil cooler. The baffles were part of a Supplemental Type Certificate (STC) SA01165CH manufactured by D'Shannon Products, Ltd. Airframe examination of the cooling air baffles by investigators confirmed that the baffles were installed and attached to the mounting studs of the engine oil cooler. The Continental Motors, Inc, FAA Approved Operator's Manual for the IO-470 states that periodic inspections should be performed at an interval of 100 hours. One of the requirements of the 100-hour periodic inspection is removal of all detachable cowling and surrounding baffles that would interfere with access to the engine components and attaching parts. Attaching parts should be checked for tightness. WRECKAGE & IMPACT INFORMATION The airplane was recovered and transported to an aircraft storage facility in Phoenix. An NTSB investigator and a technical representative from the engine manufacturer examined the airplane on October 21, 2012. A visual examination of the engine revealed cracks in the right side crankcase above the number five cylinder with dark colored stains surrounding the cracks. The bottom of the engine from the oil cooler aft was covered with a black viscous fluid that also trailed down the right side of the airframe. Under authorization of the NTSB investigator-in-charge (IIC), the propeller and baffling around the oil cooler was removed in preparation for shipment to the Continental Motors, Inc., factory in Mobile, Alabama. During this preparation, it was noted that the nuts on the bottom of the oil cooler exhibited little resistance when being removed. The oil cooler gasket between the oil cooler and oil cooler adapter plate was extruded on the bottom surface. On March 20, 2013, a full engine examination was performed at Continental Motors Incorporated, Mobile, under the oversight of the NTSB IIC. The lower half of the oil cooler gasket was deformed, and the lower center bolt hole in the gasket was ripped out. Two quarts of oil was recovered from the oil sump. Mechanical damage was observed on the interior of the engine case in the vicinity of the number five and number six cylinder positions. All six connecting rod journals on the crankshaft exhibited thermal distress and scoring, with the number 5 connecting rod journal exhibiting the most thermal discoloration, mechanical damage, and displacement of journal material. The number 5 connecting rod was separated from its end cap and was thermally discolored. The connecting rod bolts were fractured and the bolts displayed necking deformation toward their fracture surfaces. The connecting rod end cap was deformed and mechanical smear marks were observed. Connecting rod bearing material was identified in the oil sump. Light circumferential scoring from particulate matter was identified in the oil pump interior surfaces. Shiny bright particles were identified in the folds of the oil filter. Excluding the displacement of journal material on the number 5 connecting rod journal, the oil transfer passages were open and unrestricted in both the crankcase and crankshaft. With the exception of the protruded oil cooler gasket, there were no other signs of oil leaks from the engine. AIRPORT INFORMATIONThe four-seat, low-wing, retractable landing gear airplane, serial number D6732, was manufactured in 1961. It was powered by a Continental Motors IO-470-HcN10B 260-hp engine, and equipped with a McCauley constant speed propeller, model number 2A36C23-P-F-G/S84B-0. Review of copies of the airframe log book showed an annual inspection was performed on September 12, 2012, at a total airframe time of 4,760.50 hours (1,063.80 tach). The engine log book showed an annual inspection completed on September 12, 2012, at a total engine time of 3,744.0 hours, and 1,345.4 hour since major overhaul (SMOH). The hours indicated on the tach as recorded during the post-accident examination was 1,070.21. The tach time between the annual inspection and the accident was 6.41 hours. A review of the airplane's FAA Airworthiness documentation shows that an airframe modification was installed on November 7, 2002, which places cooling air baffles around the oil cooler. The baffles were part of a Supplemental Type Certificate (STC) SA01165CH manufactured by D'Shannon Products, Ltd. Airframe examination of the cooling air baffles by investigators confirmed that the baffles were installed and attached to the mounting studs of the engine oil cooler. The Continental Motors, Inc, FAA Approved Operator's Manual for the IO-470 states that periodic inspections should be performed at an interval of 100 hours. One of the requirements of the 100-hour periodic inspection is removal of all detachable cowling and surrounding baffles that would interfere with access to the engine components and attaching parts. Attaching parts should be checked for tightness. WRECKAGE & IMPACT INFORMATION The airplane was recovered and transported to an aircraft storage facility in Phoenix. An NTSB investigator and a technical representative from the engine manufacturer examined the airplane on October 21, 2012. A visual examination of the engine revealed cracks in the right side crankcase above the number five cylinder with dark colored stains surrounding the cracks. The bottom of the engine from the oil cooler aft was covered with a black viscous fluid that also trailed down the right side of the airframe. Under authorization of the NTSB investigator-in-charge (IIC), the propeller and baffling around the oil cooler was removed in preparation for shipment to the Continental Motors, Inc., factory in Mobile, Alabama. During this preparation, it was noted that the nuts on the bottom of the oil cooler exhibited little resistance when being removed. The oil cooler gasket between the oil cooler and oil cooler adapter plate was extruded on the bottom surface. On March 20, 2013, a full engine examination was performed at Continental Motors Incorporated, Mobile, under the oversight of the NTSB IIC. The lower half of the oil cooler gasket was deformed, and the lower center bolt hole in the gasket was ripped out. Two quarts of oil was recovered from the oil sump. Mechanical damage was observed on the interior of the engine case in the vicinity of the number five and number six cylinder positions. All six connecting rod journals on the crankshaft exhibited thermal distress and scoring, with the number 5 connecting rod journal exhibiting the most thermal discoloration, mechanical damage, and displacement of journal material. The number 5 connecting rod was separated from its end cap and was thermally discolored. The connecting rod bolts were fractured and the bolts displayed necking deformation toward their fracture surfaces. The connecting rod end cap was deformed and mechanical smear marks were observed. Connecting rod bearing material was identified in the oil sump. Light circumferential scoring from particulate matter was identified in the oil pump interior surfaces. Shiny bright particles were identified in the folds of the oil filter. Excluding the displacement of journal material on the number 5 connecting rod journal, the oil transfer passages were open and unrestricted in both the crankcase and crankshaft. With the exception of the protruded oil cooler gasket, there were no other signs of oil leaks from the engine. ADDITIONAL INFORMATIONEngine Oil Cooler The engine oil cooler was manufactured as a sandcast aluminum body with oil flow passages and cooling fins that allow cooling air to flow around the oil passages, cooling the oil to a temperature below 180 degrees F. The oil cooler is attached to the forward part of the engine in front of the number five cylinder using an adapter plate, a gasket, and five bolts and three studs/nuts. The oil cooler is divided into two chambers; the top and bottom. Oil enters the oil cooler through the adapter plate that is mounted between the cooler and the crankcase. The oil flows through the bottom chamber past the cooling fins, and is then routed to the top chamber past additional cooling fins. Oil then returns to the engine via the oil cooler adapter plate. Teledyne Continental Service Bulletin SB96-7C SB96-7C addresses the importance of applying the proper torque value to fasteners utilized on Continental engines. "Failure to verify a fastener's serviceability or to correctly lubricated the fastener prior to assembly and torqueing will result in the fastener not being properly pre-loaded and subsequent failure of the fastener many occur."
A loss of engine power due to oil starvation due to loose oil cooler attachment bolts. Contributing to the accident was inadequate maintenance during the annual inspection.
Source: NTSB Aviation Accident Database
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