CEN15FA056

The pilot's failure to maintain adequate airspeed and his exceedance of the airplane's critical angle-of-attack for reasons that could not be determined based on the available evidence, which resulted in an aerodynamic stall/spin. Contributing to the accident was the improperly installed oil gauge housing extension, which resulted in a loss of oil quantity and right engine power.

The airline transport pilot was conducting a cross-country repositioning flight. While en route to the destination airport, the pilot contacted air traffic control and stated that he was beginning to descend. No further radio transmissions were made by the pilot. Radar and GPS information showed, about the same time as the pilot's last transmission, the airplane's flightpath began descending in a westerly direction. The last recorded GPS point showed the airplane about 200 ft southwest of the initial impact point, 90 ft above ground level, and at a groundspeed of 66 knots. The airplane wreckage was located in an open field and impact signatures were consistent with a stall/spin, which had resulted in a near-vertical impact at a slow airspeed. The right propeller blades were found in the feathered position. Examination of the right engine found that the oil gauge housing extension was improperly secured to the oil gauge housing, which resulted in a loss of engine oil. Additionally, the examination revealed a hole in the right engine's crankcase, metal material in the oil sump, and signatures consistent with the lack of lubrication. Cockpit switches were positioned in accordance with the in-flight shutdown of the right engine. No anomalies were found with the left engine or airframe that would have precluded normal operation. Another pilot who had flown with the accident pilot reported that the pilot typically used the autopilot, and the autopilot system was found with the roll, heading, and pitch modes active. During the descent, no significant changes of heading were recorded, and the direction of travel before the stall was not optimal for the airplane to land before a fence line. It is likely that the autopilot was controlling the airplane's flightpath before the stall. Despite one operating engine, the pilot did not maintain adequate airspeed and exceeded the airplane's critical angle-of-attack (AOA), which resulted in an aerodynamic stall/spin. Correcting the last GPS recorded airspeed for prevailing wind, the airplane's indicated airspeed would have been about 72 knots, which is above the airplane's 0-bank stall speed, but an undetermined amount of bank would have been applied to maintain heading, which would have accelerated the stall speed. It could not be determined why the pilot did not maintain adequate airspeed or notify air traffic controller of an engine problem.  Although a review of the pilot's medical records revealed that he had several historical medical conditions and the toxicology tests detected several sedating allergy medications in his system, it was inconclusive whether the medical conditions or medications impaired the pilot's ability to fly the airplane or if the pilot was incapacitated. It is also possible that the pilot was distracted by the loss of oil from the right engine and that this resulted in his failure to maintain adequate airspeed, his exceedance of the airplane's critical AOA, and a subsequent stall/spin; however, based on the available evidence, the investigation could not determine the reason for the pilot's lack of corrective actions.

Engine Examinations Both engines were examined under the auspices of the NTSB investigator-in-charge. The left engine was impact damaged and a test run could not be performed. The engine was torn down and inspected. Of note, the oil gauge housing extension was secured. No anomalies were detected with the left engine which would have precluded normal operation. In addition to the hole in the crankcase, the right engine was impact damaged and a test run could not be performed. The left magneto and ignition harness were both impact damaged and could not be tested. The oil sump was opened and found to contain metallic material consistent with connecting rods, bearings, and crankcase material. The oil pickup screen contained a small amount of metallic material. The oil pump was disassembled and metallic material was present in the oil pump gears along with scoring on the pump housing consistent with passage of hard material. The oil screen contained a significant amount of metallic material on the screen. The oil gauge housing extension was been was found separated from its housing at the accident site. No impact damage was noted to the housing extension. The hose and clamps were not positioned in a way to place the oil gauge housing extension joint in the middle of the hose. According to manufacturer specifications, the hose should be centered over the connection joint. The top hose clamp was placed below the oil gauge housing extension bead. The extension bead is designed to be securely fitted against the oil gauge housing. In addition, it was also noted that the hose material was not the material specified by the manufacturer. Examination of the engine bearings found signatures consistent with lubrication distress with scoring and thermal smearing of the surface babbit. Connecting rods 1 and 2 had separated from their respective journals. All connecting rods and rod bearings displayed signatures of thermal discoloration consistent with lubrication distress. The engine log books did not contain any recent entries of work performed concerning on the oil gauge housing extension. Several entries documented oil changes to include a check for oil leaks. The last entry dated November 18, 2014, reported "[r]eplaced oil with Aero Shell 100W oil, cleaned engine from excess oil and checked for oil leaks, none found. Ops check good, returned to service." The entry was endorsed by the pilot, who was also one of the mechanics that maintained the airplane. Garmin GPSMap 296 Data from the GPS unit was downloaded and found to contain the accident flight. The data field for the accident flight's date was recorded as April 9, 1995, but the time and route of flight remained consistent with the accident flight. The airplane departed the David Wayne Hooks Memorial Airport about 0854. It departed the airport to the south before turning west towards Austin, Texas. While en route the airplane cruised about 6,700 feet mean sea level (msl) and about 138 knots groundspeed. At 0927, the airplane began to descend and the groundspeed decreased. The ground track varied between 270-290° but averaged 281° close to the pre-descent heading of 282°. The average descent rate was 440 feet per minute. The last recorded point was recorded at 0944:35 with the airplane about 200 feet southwest of the initial impact point, at a GPS altitude of 610 feet msl, groundspeed of 66 knots, and descent rate of 290 feet per minute. Terrain elevation at that location was approximately 520 feet msl. Aero Commander 500A Speeds A review of the operator's manual for the Aero Commander 500A found that the minimum control speed, which is the minimum speed at which the airplane is controllable in flight, with sudden failure of one engine and takeoff power on the other engine is 61 knots. At its maximum gross weight, the stall speed with zero-degrees of bank is 63 knots with the flaps up and 57 knots with the flaps down. Aero Commander 500A Engine Failure During Cruise The published procedure for an engine failure during cruise flight is as follows: 1. Correctly determine inoperative engine by checking with throttles. 2. Feather engine as outlined in Propeller Section of the Normal Operating Procedures. 3. Maintain 70% power on the operative engine for best cruise. The procedure to feather an engine as found in the Propeller Section of the Normal Operating Procedures is as follows: 1. Throttle – CLOSED (inoperative engine) 2. Mixture control – IDLE CUTOFF (inoperative engine) 3. Fuel valves – CLOSED (inoperative engine) 4. Ignition switch – OFF (inoperative engine) 5. Propeller control – FEATHER RANGE NOTE: The above feather procedure is for normal operation. For emergency use, propeller may be feathered first. Assessment of the Pilot's Abilities An employee of the company, also a flight instructor, provided an assessment of the pilot's flying ability. This employee flew most recently from October 20 to November 7, 2014, with the accident pilot. During this time he was able to observe the pilot's flying ability since he was seated in the right cockpit seat. The employee recalled the pilot had a habit of engaging the autopilot for every ferry leg on flights to and from the survey lines. For long distances, the pilot flew between 6,000 – 9,000 feet msl. He reported that the pilot was very comfortable with the airplane and easily landed with strong winds. During instrument meteorological conditions, the pilot maintained good control of the airplane. On one of the flights, the right engine's oil temperature reading was "abnormal" so the flight returned back to the KDWH where the issue could be fixed. The pilot routinely preflighted the airplane daily and after every fuel servicing, and routinely inspected oil and fuel quantities. A notebook that was maintained by the accident pilot was found in the wreckage. Between the dates of October 20 and November 7, there were no notes about an oil malfunction. There were also no maintenance log book entries between those dates concerning corrective maintenance of either engine's oil system. An autopsy was conducted on the pilot by the Deputy Medical Examiner as authorized by the Justice of the Peace, Precinct 4 for Lee County, Texas. The autopsy noted the cause of death as a result of blunt force injuries and the manner of death was an accident. The FAA Civil Aerospace Medical Institute performed forensic toxicology tests on specimens from the pilot. Findings were negative for carbon monoxide and ethanol. The following drugs were detected: 22 (ug/ml, ug/g) Acetaminophen detected in Urine Azacyclonol detected in Urine Azacyclonol NOT detected in Blood (Cavity) Cetirizine detected in Urine Cetirizine detected in Blood (Cavity) Diphenhydramine detected in Urine 0.053 (ug/ml, ug/g) Diphenhydramine detected in Blood (Cavity) Fexofenadine detected in Blood (Cavity) Fexofenadine detected in Urine Naproxen detected in Urine Fexofenadine is a prescription and over-the counter antihistamine used to relieve the allergy symptoms of seasonal allergic rhinitis (''hay fever''). It is marketed as a non-sedating antihistamine. Azacyclonol is a minor metabolite of fexofenadine. Cetirizine is an over-the-counter antihistamine is used to temporarily relieve the symptoms of hay fever and allergy to other substances. This medication causes drowsiness and could impair mental and/or physical ability required for the performance of potentially hazardous tasks (e.g., driving, operating heavy machinery). The FAA recommends waiting at least 48 hours after the last dose before performing safety related duties. Diphenhydramine is an over-the-counter antihistamine used to treat allergic conditions and as a sleep aid. This medication causes drowsiness and could impair mental and/or physical ability required for the performance of potentially hazardous tasks (e.g., driving, operating heavy machinery). The FAA recommen