N337LCCessna 337G · 1976

On November 11, 2011, at 1615 mountain standard time a Cessna 337G, N337LC, registered to LAMP Ministry LLC, of New Haven, Michigan, was destroyed when it impacted the ground shortly after takeoff from runway 20 at the San Luis Valley Regional Airport/Bergman Field (ALS), Alamosa, Colorado. The airplane was being operated under the provisions of 14 Code of Federal Regulations Part 91. The pilot, who was the sole occupant, sustained fatal injuries. Visual meteorological conditions prevailed and no flight plan was filed. The flight's intended destination was Harriet Alexander Field (ANK), Salida, Colorado.

A witness located at the airport observed the pilot start the airplane (both engines). She did not see the airplane taxi or takeoff. Another witness, who was located south of the accident site, saw the airplane traveling east at a low altitude. Then he thought he heard the engine shut off and airplane went out of sight behind a stand of trees. The witness then heard a "pop", then, another "pop." Another witness, driving in a car nearby the accident site saw the airplane flying to the east when it suddenly lost altitude and nose dived toward the ground. This witness lost sight of the airplane behind trees and did not see the airplane impact the ground.

The accident pilot, who had over 3,650 total hours of flight time in single and multi-engine airplanes, 565 hours of which were time in the Cessna 337. He had been flown to Alamosa by another ministry pilot on the morning of the accident. The reason for the trip was to pick up the airplane after it's annual inspection was completed in Alamosa. The ministry pilot stated that the accident pilot was in good spirits and did not express any concerns. Both the accident pilot and ministry pilot discussed what work was done to the airplane during the annual inspection. The ministry pilot also stated that the pilot displayed very good aeronautical knowledge and flying skills and that his last bi-annual flight review was conducted in the Cessna 337 sometime during June of 2010.

According to tachometer times entered in the aircraft journey log, between October 29, 2010 and November 1, 2011, the accident pilot flew the accident aircraft 124.1 hours. He held Commercial Pilot certificates for single and multiengine airplanes and held an instrument rating in airplanes. The pilot's most recent FAA medical certificate (Second Class) was dated June 6, 2011. The medical certificate noted that the pilot "must wear corrective lenses and possess glasses for near and intermediate vision".

The airplane was a 1976 Cessna Skymaster 337G, S/N: 33701672. The twin engine airplane's fuselage had two engines in tandem, one in front of the cabin and one engine behind the cabin. The airplane was equipped with retractable landing gear and a belly-attached cargo pod.

The airplane had been in Alamosa since October 15, 2011, undergoing an annual inspection, which was completed on November 1, 2011. The flight was the first flight after the annual inspection. According to airport personnel, 35.1 gallons of fuel (topped off) was added to the right wing tank prior to takeoff.

Log Book Review

Fire damaged aircraft journey logs with a start date of 1999 were recovered from the aircraft. The journey log recorded detailed flight times for individual flights and maintenance entries for the aircraft. Based on annotations in the journal, the aircraft was regularly flown in Canada from 1999 until December 2005. An entry dated December 12, 2005 was followed by an entry dated October 29, 2010. Starting with the October 29th entry, the accident pilot was the only listed pilot for the aircraft in the journal. The aircraft's last annual inspection was completed on November 1, 2011.

According to the journey log and an interview with the repair station manager, the aircraft was flown to Alamosa on October 15, 2011*, with a tachometer total time of 4385.5 (hour meter 2113.6) to undergo an annual inspection that began on October 17, 2011. Based on last annual inspection entry in the journey log (November 1, 2011), the front engine Total Time (TT) was 1769.2 hours and Total Time Since Overhaul (TTSO) was 114.5 hours. The rear engine TT was 1420.9 hours and TTSO was 114.6 hours. Front and rear propeller TTs were 605.2 hours respectively. Each propeller had a TTSO of 114.6 hours.

Also recovered from the wreckage were fire damaged individual logbooks for the front and rear engines and propellers.

Front Engine

The front engine was factory rebuilt in April of 1995 by TCM. In April of 2001, at 1001.9 hours, the engine was removed for repair and a new crankshaft was installed. The engine was reinstalled on the aircraft. In March of 2002, at 1164 hours, the engine was removed for propeller strike and reinstalled. An entry dated December 12, 2005 was followed by an entry dated May 5, 2009. The May 5th entry showed that the engine was removed for overhaul at 1654.6 hours Since Major Overhaul (SMOH). The engine was reinstalled on October 25, 2010. The last entry was dated November 1, 2011 (annual inspection). The front propeller was removed and overhauled at 490.6 hours TT on October 25, 2010. The propeller was then reinstalled on October 28, 2010.

Rear Engine

The rear engine was factory rebuilt in February 1998 by TCM. In March 2002 at 815.7 hours SMOH, the engine was removed, repaired and reinstalled due to propeller strike. An entry dated January 2, 2005, 1160 hours SMOH, was followed by an entry dated October 28, 2010, 1306.3 hours TT and 0.0 hours SMOH. The last entry dated November 1, 2011 was an annual inspection. The rear propeller was overhauled on March 3, 2010. The propeller was reinstalled had an annual inspection on October 28, 2010 at 490.6 hours TT. An entry dated November 1, 2011 showed a total time of 345 hours TT.

Local witnesses stated that the weather was mild with variable light wind.

The airplane was not equipped with hardened recording devices. The investigative team searched the wreckage for any evidence of installed non-volatile memory devices. Due to the extent of the thermal damage to the airplane it is unknown at this time whether any of these memory devices were onboard the airplane.

General

The accident site was located at N37 degrees, 24.631 minutes, W105 degrees, 52.349 minutes, at an elevation of 7,544 feet. The site was 0.89 miles south of the departure end of Runway 20. Initial observations of the wreckage showed evidence that the rear propeller was not producing power at impact and the fuel valve to the rear engine was observed to be in the closed position. There was evidence that the forward engine was producing power at the time of impact. Neither the uplocks nor downlocks for the main landing gear were engaged, but due to impact damage, the actual landing gear position at impact could not be confirmed. Flight control cable continuity was confirmed from the cabin floor under the front seats to each flight control. Control cable continuity could not be fully assessed on scene due to extreme impact and fire damage to the front of the airplane.

Airframe

The aircraft impacted a relatively level cow pasture on a heading of approximately 070 degrees in a wings level, 45-degree nose down attitude. No ground contact marks were observed before the main wreckage. A post-impact fire consumed a majority of the fuselage, including the cockpit, between the rear and front firewalls. Portions of both wing roots were also consumed by the post impact fire. The post-impact fire initiated a small grass fire in front of the aircraft. The post-impact fire consumed mostly all of the cabin section and all of the cockpit flight and engine monitoring instruments. A latched and partially fire damaged seat belt was found on the left side of the fuselage.

Landing Gear System

Neither the uplocks nor downlocks for the main landing gear were engaged, which could indicate that the landing gear may have been in transit, but due to the severe impact damage, the actual landing gear position at impact could not be confirmed. The left main wheel and tire assembly exhibited damage similar in shape to a propeller blade cut.

Flight Controls

All of the flight controls remained attached. The right wing's leading edge exhibited slight aft crushing at the wing root. The remainder of the leading edge and the left wing's leading edge did not exhibit aft crushing damage. The two tail booms were partially fractured and each was bowed outboard. No leading edge damage was present to the front of the horizontal stabilizer. Flight control cable continuity was confirmed from the cabin floor under the front seats to each flight control. Control cable continuity could not be assessed on scene due to extreme impact and fire damage to the front of the airplane. The flap actuator, which was separated from its mounting structure, was in a retracted position.

Engines / Propellers General

The front engine was partially buried in the ground at a nose down angle between 30 and 45 degrees. It was attached to the aircraft firewall. The front propeller was partially attached to its engine flange. One blade exhibited double S-bending. The rear engine was also attached to the firewall. The rear propeller was found separated from its engine flange and approximately 100 feet in forward of the aircraft wreckage. No rotation marks were noted to the propeller. The leading edge of one of the blades had several deep gouges. Neither propeller assemblies (front and rear engine) were in the feather position. The power control quadrant in the cockpit exhibited extreme fire damage, however, all engine and propeller controls were found in the full forward position

Front Engine

The front engine remained partially attached to the airframe via the engine mount, control cables, hoses and wires and exhibited thermal damage. The engine oil sump was fractured into several pieces. A section of the accessory case was separated. The starter, starter adaptor, magnetos and starter adaptor were fractured free of the engine. The propeller remained partially attached to the engine crankshaft propeller flange. One propeller blade exhibited "S" shaped bending and gouges in the leading edge.

Rear Engine

The rear engine remained partially attached to the airframe via the engine mount, control cables, hoses and wires and exhibited thermal damage. The propeller and engine crankshaft propeller flange were separated from the engine at the engine crankshaft nose seal and were located forward of the main wreckage. Aft bending midway from the propeller hub and gouges in the trailing edge were observed in one blade of the propeller.

Fuel System

The outboard fuel tanks in the left wing appeared intact. The both wings' inboard tanks and the right wing outboard tanks were partially consumed by fire. The front engine selector handle was set to the left tank. The front engine fuel selector valve was between the left tank and off positions. The rear engine fuel selector handle and valve were in the off position.

Due to the severe thermal damage resulting from a fuel fed post-impact fire, the airplane was moved to a facility for more detailed examinations of the airframe and engines. Detailed examinations of the airframe and engine teardowns were conducted at Beegles Air Salvage, Greeley, Colorado on November 14, 2011.

Airframe Observations

Control cable continuity was confirmed for the elevator and ailerons from the cabin floor to the control yokes. The rear engine cowling exhibited damage consistent with propeller cuts. The main landing gear were not locked in either the extended or retracted positions. The main landing gear legs were in an intermediate position with the legs folded back and the wheels oriented upward near the main gear wheel wells. The nose gear appeared to be in the retracted position. The two leading edge gouges on rear propeller blade "A" (9" and 12" inboard from the tip) appeared to line up with the damage to the left main gear axle and wheel hub when the propeller blade was placed next to the damaged left main wheel. The two fuel selector valves were removed from the aircraft structure and found to function normally. The rear fuel strainer screen was clear of debris. The front fuel strainer was not located in the wreck-age. All of the cockpit engine controls were in the full forward position.

Engine / Propeller Observations

Front Engine – IO-360-G (2), serial number 244582-R

McCauley Propeller – D2AF34C306-B, serial number 010231

The propeller was partially attached to the crankshaft flange and all of the cylinders remained attached to the crankcase. The alternator, both left and right magnetos, and the starter were separated from the engine due to impact forces. The exhaust system and air induction system exhibited impact damage. Both left and right magneto drive shafts did not rotate freely when turned by hand, however, the cotter pins on the magneto drive shafts were intact. Both magnetos were disassembled and examined. The distributor driven and drive shaft drive gears were found intact. The magneto drive coupling rubber bushings were missing. The ignition harness exhibited thermal damage. The top spark plugs exhibited normal operating signatures in accordance with the Champion aviation check-a-plug comparison chart. The bottom spark plugs were inspected using a lighted borescope and exhibited normal operating signatures in accordance with the Champion aviation check-a-plug comparison chart.

The fuel pump had been displaced toward the rear of the engine due to impact forces. A portion of the mixture control cable remained attached to the mixture control lever and was near the lean position. The fuel pump drive coupling exhibited impact damage. The fuel pump was disassembled and the fuel pump vanes were found intact. No indication of hard particle passage was observed in the fuel pump housing. The relief valve seat exhibited no obstructions and the diaphragm was intact with no indication of fuel leakage in the chamber side of the diaphragm.

The fuel manifold valve was disassembled and the screen was found clear of obstructions. The diaphragm exhibited damage and the plunger and diaphragm retaining nut was found tight and secure. No scoring was observed on the fuel valve assembly. No indication of fuel leakage was observed in the vent chamber side of the diaphragm. All fuel injector lines remained attached to their respective fuel injector nozzles. All fuel nozzles were clear of obstructions. The throttle fuel control throttle lever and throttle plate were observed near the idle position.

A portion of the oil sump was not located. The oil screen was clear of obstructions and a residue of oil was present.

All cylinders were inspected using a lighted borescope. The internal combustion chambers exhibited a material consistent with that of normal combustion deposits. The cylinder bores were clear of scoring and no evidence of hard particle passage was observed in the cylinder bore ring travel area. All overhead cylinder components exhibited a residue of oil. The intake and exhaust valve faces were inspected using a lighted borescope. The intake and exhaust valve faces exhibited a material consistent with that of normal combustion deposits. All rocker arms were intact and exhibited a residue of oil. The piston heads were examined using a lighted borescope and exhibited a material consistent with that of normal combustion deposits.The crankshaft exhibited continuity through the oil sump opening and a residue of oil was present. Spiral cracking was observed aft of the crankshaft flange.

The starter and alternator had impact damage. The vacuum pump drive shaft did not rotate by hand. The vacuum pump was disassembled and the rotor and vanes were found intact.

The propeller governor control cable remained attached to the propeller governor control lever. The control lever was moved through its full range of travel by hand. The propeller governor drive shaft rotated by hand. The propeller governor oil screen was clear of obstructions The two-bladed, variable-pitch propeller, remained partially attached to the crankshaft flange. Both propeller blades exhibited chordwise scratches, polishing, and leading edge damage. One propeller blade exhibited a bend toward the cambered side of the propeller blade, beginning near the propeller blade root.

No pre-impact anomalies were found during the front engine examination.

Rear Engine – IO-360-GB, serial number 813007-R

McCauley Propeller – D2AF34C307-B, serial number 000235

The engine mount and firewall remained attached to the engine. The engine crankshaft propeller flange was separated and located with the propeller. All of the cylinders remained attached to the crankcase and all damage observed was consistent with impact forces. The exhaust system and the induction system exhibited impact damage. Both magneto drive gears turned freely by hand and their respective cotter pins on the magneto drive shafts were intact. Both magnetos were disassembled and examined. The distributor driven and drive shaft drive gears were found intact and the magneto drive coupling rubber bushings were intact. The ignition harness exhibited thermal damage. The top spark plugs exhibited normal operating signatures in accordance with the Champion aviation check-a-plug comparison chart. The bottom spark plugs were inspected using a lighted borescope and exhibited normal operating signatures in accordance with the Champion aviation check-a-plug comparison chart.

The fuel pump remained intact, was attached to the engine, and exhibited thermal damage. The mixture control lever moved from stop to stop by hand and the fuel pump drive coupling was intact. The fuel pump did not turn freely by hand and was disassembled. The fuel pump vanes and rotor exhibited a molten material and the diaphragm exhibited thermal damage. This thermal damage was due to the post-impact fire. The fuel manifold valve was intact and safety wired. The fuel manifold valve was disassembled and the screen was clear of obstructions. The plunger and diaphragm retaining nut was tight and secure. No scoring was observed on the fuel valve assembly. No indication of fuel leakage was observed in the vent chamber side of the diaphragm. A residue was observed in the fuel manifold assembly. All fuel injector lines remained attached to their respective fuel injector nozzles and all fuel nozzles were clear of obstructions.

The oil screen was safety wired, clear of obstructions, and a residue of oil was present.

All cylinders were inspected using a lighted borescope. The internal combustion chambers exhibited a material consistent with that of normal combustion deposits. The cylinder bores were clear of scoring and no evidence of hard particle passage was observed in the cylinder bore ring travel area. Suction and compression were obtained on all cylinders at the top spark plug hole when the crankshaft was rotated by hand with an adaptor in the propeller governor drive. All overhead cylinder components exhibited a residue of oil and exhibited movement when the crankshaft was rotated. The intake and exhaust valve faces were inspected using a lighted borescope. The intake and exhaust valve faces exhibited a material consistent with that of normal combustion deposits. All rocker arms were intact and exhibited a residue of oil. The piston heads were examined using a lighted borescope and exhibited a material consistent with that of normal combustion deposits. The crankshaft exhibited continuity to the valve train and accessory gears.

The starter and the alternator exhibited thermal and impact damage. The vacuum pump drive shaft exhibited thermal damage and did not rotate by hand. The vacuum pump was disassembled and the rotor and vanes were intact.

The propeller governor exhibited impact damage and was fractured near the base. The propeller governor control lever was fractured free of the governor. The propeller drive gear was fractured and the propeller governor oil screen was clear of obstructions.

The propeller and crankshaft propeller flange were separated from the engine. The blades were labeled A and B for identification. Blade A was bent aft from the hub to the tip. Two large gouges were observed in the leading edge of blade A, 9 and 12 inches from the tip. Chordwise scratches to the cambered side of the blade were observed approximately midway from the hub to the tip. Blade A was fractured and loose in the hub. Blade B exhibited chordwise scratches to the cambered side of the blade approximately midway from the hub to the tip.

An autopsy did not reveal any pre-existing medical conditions that could have contributed to the accident. Toxicology tests on the pilot were negative.

Performance Calculations

The actual weight of the aircraft at the time of the accident could not be determined due to a lack of fuel and aircraft empty weight information. A weight of 4,000 pounds, the lightest weight shown in the POH, was used for the following calculations. The POH noted that the normal rate of climb and single engine rate of climb for the aircraft is reduced 15 feet per minute with the belly cargo pod attached.

According to the POH, the following conditions were used to determine the normal rate of climb for the aircraft: flaps and gear up, 2600 RPM, 24 inches Hg manifold pressure or full throttle, cowl flaps open, an airspeed of 110 KIAS. The normal rate of climb at a pressure altitude of 7,000 feet, at 0°C with the belly cargo pod attached is 672 feet per minute.

According to the POH, the following conditions were used to determine the single engine rate of climb for the aircraft: flaps and gear up, 2800 RPM, full throttle, mixture set in accordance with placarded fuel flow, cowl flaps open on the operating engine, cowl flaps closed on the inoperative engine, inoperative engine's propeller feathered, and an airspeed of 85 KIAS. The single engine rate of climb with the rear engine operating at a pressure altitude of 7,000 feet, a temperature of 0°C, and the belly cargo pod attached is 142 feet per minute. The single engine rate of climb with the front engine operating at a pressure altitude of 7,000 feet, a temperature of 0°C, and the belly cargo pod attached is 99 feet per minute.

According to the POH, the rate of climb is reduced 110 feet per minute with the landing gear extended. The rate of climb is reduced 240 feet per minute when the gear is in transit.

The airplane wreckage was released to the owner's representative.