History of Flight
On October 18, 2012, at 1040 mountain standard time, a Hawker Beechcraft N35, registration N671VC, experienced a loss of engine power while en route to Phoenix Deer Valley Airport in Phoenix, Arizona. The pilot conducted a forced landing approximately 10 miles northwest of the airport in desert terrain. The airplane was owned and operated by the private pilot under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The flight had departed Prescott, Arizona, at 1009.
The pilot reported that after contacting Phoenix Approach Control while over mountainous terrain, he observed engine oil pressure dropping below 30 psi. He determined that his destination, Deer Valley Airport, was the nearest suitable airport and continued toward it. Shortly thereafter, oil pressure fell to zero and the engine began to shake violently. The pilot shut down the engine, declared an emergency, and pressed the 'nearest' button on the GPS, which identified Pleasant Valley Airport as the closest. He turned toward that airport but lacked sufficient altitude to glide the entire distance. He executed a forced landing in desert terrain about 2.8 miles east of Pleasant Valley Airport. During the landing, the nose and left wing sustained substantial damage. Post-landing photographs showed oil and dirt streaks along the right side of the airplane emanating from the engine cowling.
Pilot Information
The 69-year-old pilot held a private pilot certificate with ratings for airplane single-engine land and instrument airplane, issued March 11, 2006. He also held a third-class airman medical certificate issued September 29, 2011, with a limitation requiring corrective lenses. The pilot reported total flight time of 4,782 hours, including 2,403 hours in the accident airplane make and model. In the 90 days preceding the accident, he had flown 24 hours, with 7 hours in the last 30 days.
Aircraft Information
The 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-horsepower engine and equipped with a McCauley constant speed propeller, model 2A36C23-P-F-G/S84B-0. Annual inspection records showed an inspection performed on September 12, 2012, at a total airframe time of 4,760.5 hours (1,063.80 tach). The engine log indicated the same inspection at a total engine time of 3,744.0 hours and 1,345.4 hours since major overhaul. Post-accident tach time was 1,070.21 hours; the interval between the annual inspection and the accident was 6.41 tach hours.
A review of FAA airworthiness documentation revealed that an airframe modification was installed on November 7, 2002, placing cooling air baffles around the oil cooler. These baffles were part of Supplemental Type Certificate SA01165CH manufactured by D'Shannon Products, Ltd. Examination of the baffles confirmed they were installed and attached to the oil cooler mounting studs.
The Continental Motors FAA-approved operator's manual for the IO-470 specifies periodic inspections at 100-hour intervals. One requirement is removal of all detachable cowling and surrounding baffles that could interfere with access to engine components and attaching parts, which should be checked for tightness.
Wreckage and Impact Information
The airplane was recovered and transported to a storage facility in Phoenix. On October 21, 2012, an NTSB investigator and a technical representative from the engine manufacturer examined the airplane. Visual examination revealed cracks in the right side crankcase above the number five cylinder, with dark stains around 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 NTSB authorization, the propeller and baffling around the oil cooler were removed for shipment to the Continental Motors factory in Mobile, Alabama. During this process, the nuts on the bottom of the oil cooler exhibited little resistance when removed. The oil cooler gasket between the cooler and adapter plate was extruded on the bottom surface.
On March 20, 2013, a full engine examination was conducted at Continental Motors under NTSB oversight. 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 were recovered from the oil sump. Mechanical damage was observed on the interior of the engine case near the number five and six cylinder positions. All six connecting rod journals on the crankshaft showed thermal distress and scoring, with the number five journal exhibiting the most thermal discoloration, mechanical damage, and material displacement. The number five connecting rod was separated from its end cap and was thermally discolored. The connecting rod bolts were fractured and displayed necking deformation near fracture surfaces. The end cap was deformed with mechanical smear marks. Connecting rod bearing material was found in the oil sump. Light circumferential scoring from particulate matter was noted on interior surfaces of the oil pump. Shiny bright particles were identified in the folds of the oil filter. Excluding the displacement of journal material on the number five journal, oil transfer passages were open and unrestricted in both the crankcase and crankshaft. No other oil leaks were found except for the protruded oil cooler gasket.
Additional Information
The engine oil cooler was manufactured as a sandcast aluminum body with oil flow passages and cooling fins, attached to the forward part of the engine in front of the number five cylinder using an adapter plate, a gasket, five bolts, and three studs/nuts. The cooler is divided into top and bottom chambers; oil enters through the adapter plate, flows through the bottom chamber past cooling fins, then to the top chamber, and returns to the engine.
Teledyne Continental Service Bulletin SB96-7C addresses proper torque application to fasteners on Continental engines, stating that failure to verify fastener serviceability or to correctly lubricate fasteners before assembly and torqueing may lead to inadequate preload and subsequent failure.