Cessna 421C Engine Failure

On July 9, 2011, about 1740 central daylight time, a Cessna 421C, operated by a private individual, was substantially damaged when it impacted terrain while on approach to the Demopolis Municipal Airport (DYA), Demopolis, Alabama. The certificated private pilot and six passengers were fatally injured. Visual meteorological conditions prevailed and an instrument flight rules flight plan was filed for the flight that departed the Creve Coeur Airport (1H0), St. Louis, Missouri, destined for the Destin-Ft. Walton Beach Airport (DTS), Destin, Florida.

According to information obtained from the Federal Aviation Administration (FAA), the pilot was in cruise flight at flight level 210 (21,000 feet), and in contact with the Atlanta air route traffic control center when he declared an emergency due to a rough running engine, about 1725. He diverted to DYA, which was located 12 o’clock and about 10 miles from the airplane’s position. The pilot was switched to Meridian Approach and he reported descending through 17,000 feet mean sea level (msl) at 1727:55, with the airplane positioned about 2.5 miles northeast of the airport. The pilot further stated that he planned to orbit over Demopolis during the descent. At 1728:59, the pilot confirmed that he was experiencing a rough running engine; however, about 10 seconds later, he reported that he had just shut down the right engine. He also stated he did not believe he would require any assistance after landing. At that time, the airplane was about 6 miles east of DYA, at an altitude of about 14,500 feet msl.

The pilot reported the airport in sight, was cleared for a visual approach and then approved for a frequency change to the local common traffic advisory frequency about 1734. At that point, the airplane was about 2.5 miles northeast of the airport, at an altitude of about 7,000 feet. There were no further communications received from the airplane. The airplane’s radar track was consistent with a left traffic pattern approach to runway 22. The airplane was descending from an altitude of about 2,300 feet msl, when it was abeam the runway threshold, on the downwind leg of the traffic pattern. The last radar target was observed at 1739, at an altitude of 700 feet on the base leg of the traffic pattern, about 3 miles from the approach end of runway 22, and about .5 miles northwest of the extended centerline.
The airplane impacted trees in a wooded area, about .8 miles north of the runway 22 threshold.

Personnel Information

The pilot, age 42, held a private pilot certificate, with ratings for airplane single-engine land, multiengine land, and instrument airplane. His most recent FAA third-class medical certificate was issued on July 19, 2007.
At the time of his most recent FAA medical certificate, the pilot reported a total flight experience of 642 hours.
The pilot’s flight instructor reported that the pilot had practiced at least seven single-engine landings in the accident airplane, which included at least three single-engine landings from a VFR traffic pattern. The pilot completed Cessna 421 recurrent training on July 29, 2010, which included three practice single-engine landings at that time.
Based on the hours that the accident airplane had been operated, the pilot’s total flight time at the time of the accident was estimated to be about 1,000 hours, which included about 500 total hours of multiengine flight experience.

Aircraft Information

The eight-seat, low-wing, retractable-gear Cessna 421C, was manufactured in 1978. It was powered by two Continental Motors, Inc., GTSIO-520-L, 375-horsepower engines, each equipped with a McCauley propeller assembly.
The most recent recorded airframe logbook entry was on February 10, 2011, with no change in flight hours since the annual inspection. At that time, the left engine hydraulic filter and right main landing gear strut were replaced.
The left engine was overhauled on August 31, 2007, at a total time in service of 3,780.7 hours. It was installed on September 28, 2007. At the time of the most recent annual inspection, the left engine had accumulated approximately 305 hours since overhaul.

The right engine was overhauled on August 24, 2004, at a total time in service of 1,595.7 hours. It was installed on September 30, 2004. At the time of the most recent annual inspection, the right engine had accumulated approximately 514.2 hours since overhaul. The most recent recorded right engine logbook entry was on February 10, 2011, and noted a reset of the engine fuel pressures.

An oil analysis report of oil samples collected from each respective engine on January 3, 2011, stated that the samples “appeared normal.” Both propellers were overhauled on June 1, 2010.

At the time of the annual inspection, they had been operated for about 172 hours. According to a work order for a pre-purchase inspection, as of June 3, 2011, the airplane had been flown approximately 27 hours since the most recent annual inspection.

Wreckage Information

The airplane came to rest inverted in a wooded area with varied tree heights up to about 80 feet, in a flat attitude on a course of about 100 degrees. The cockpit, the cabin up through 40-inches forward of the tail cone, and the left wing were consumed by fire.

A series of tree strikes were observed about 50 feet above the ground, approximately 70 feet south of the main wreckage. A navigation antenna was observed about 200 feet south-southeast of the main wreckage. The course from the antenna to the main wreckage was about 020-degrees.

All major portions of the airplane were accounted for at the accident site. There was no longitudinal deformation of the fuselage noted. The radar dome on the nose of the airplane was observed installed and retained its shape. All three landing gear actuators were observed in the extended position.

Portions of the flaps that were not compromised due to fire and or impact damage were extended approximately 40 degrees. The entire right wing was separated at the root and came to rest against a tree adjacent to the main wreckage.
The left engine and propeller assembly remained attached to the left wing and were fire damaged. The left propeller was observed a low pitch position and displayed signatures consistent with rotation at impact.

On-site examination and a subsequent teardown of the left engine at Continental Motors, Inc. (CMI), Mobile, Alabama, did not reveal any preaccident mechanical malfunctions or failures that would have precluded normal operation.
The right engine and propeller assembly remained attached to the right wing. One propeller blade was separated from the hub. The remaining two right propeller blades were observed at or near the feathered position and did not display evidence of rotation. All of the cylinders and accessories remained attached to the crankcase. The top spark plugs were removed. Their electrodes were intact and exhibited normal operating signatures in accordance with the Champion aviation check-a-plug comparison chart. The fuel pump was removed. Its respective coupling was intact; however, the camshaft gear exhibited damage on its respective gear teeth when viewed through the fuel pump bay.

The right engine was disassembled at CMI under the supervision of an NTSB investigator. The disassembly revealed additional damage and several missing teeth on the cam gear, and intake and exhaust valve contact on all six piston faces. The safety wire securing a cam gear bolt was broken at the head of the bolt, and a corresponding piece of safety wire was found in the oil sump, which contained metallic debris. The No. 1 crankshaft main and connecting rod bearings exhibited damage consistent with lubrication distress. The remaining crankshaft main and connecting rod bearings were intact and did not display evidence of lubrication distress.

The crankcase halves, camshaft, camshaft gear with separated gear teeth, cluster gear, crankshaft gear, No. 1 main bearing, camshaft and crankshaft gear attachment bolts, safety wire removed from the camshaft gear attachment bolts, and contents retrieved from the oil sump were retained and forwarded to the Safety Board’s Materials Laboratory, Washington, DC, for further examination.
A subsequent teardown of both propeller assemblies at McCauley, Wichita, Kansas, did not reveal any preaccident mechanical malfunctions or failures that would have precluded normal operation.

Tests and Research

Examination of the retained components retrieved from the right engine was performed by an NTSB materials engineer. According to the Materials Laboratory Factual Report, the camshaft gear contained 60 teeth. Forty-five of the teeth were either fractured or crushed, two teeth were damaged on the tooth flank, and 13 teeth were intact. Fracture features of the teeth with discernible fracture features were mostly uniform matte gray in the middle portion of the fracture with smeared features near the flank root surfaces. A smooth curving arrest line was observed on the fracture at the contact side of one of the teeth, with radial features emanating from the boundary. Additional examination of the fracture revealed features consistent with fatigue in steel under relatively high stress concentration. The respective adjacent gear teeth did not contain evidence of fatigue; however, another gear tooth displayed evidence consistent with surface spall.
No evidence of fretting was observed on the camshaft and cluster gear attachment bolts. Fracture features on the broken safety wire were consistent with overstress.

Examination of the crankcase revealed staining and impressions consistent with the application of silk thread around the through bolt holes on each side of the main bearing saddles at every main bearing location, and at the bolt holes at all of the camshaft main saddles.

Teledyne Continental Motors Service Information Letter SIL99-2A, dated August 27, 2002, provided information pertaining to the application of sealants, lubricants, and adhesives during maintenance, overhaul, or component repair or replacement. Page 16 of SIL99-2A contained a threading diagram for the GTSIO-520, and included a warning that stated, “Apply thread and Permatex only as illustrated.” Thread application locations were depicted at the edges of the crankcase and around the through-bolt holes in the saddle bosses for all the camshaft main journals; however, no thread was called for around the through-bolt holes at any of the crankshaft main bearing saddle bosses.

The crankcase from the right engine was returned to CMI for measurement of the main bearing bores with and without the application of silk thread in accordance with SIL99-2A. In both cases, the crankcase was assembled and torqued to the current CMI production procedures.

Measurement of the main bearing bores with the silk thread installed ranged from zero difference to +.0006 inches, with +.0004 inches observed on the No.1 main bearing bore.

According to a CMI representative, the main bearing in that location had a .006 minimum crush on each half when installed in the crankcase and the installation of silk thread alone would not result in the damage observed during the teardown inspection or affect engine performance.

The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot’s failure to maintain airplane control during a single-engine approach and his failure to fly an appropriate traffic pattern for a single-engine landing.

Contributing to the accident was a total loss of engine power on the right engine due to a fatigue failure of the right engine cam gear.