N5626D

HISTORY OF FLIGHTOn June 28, 2015, at 1745 eastern daylight time, a Beech A36, N5626D, impacted a residence and terrain following a total loss of engine power near Plainville, Massachusetts. The commercial pilot and two passengers were fatally injured, and the airplane was consumed by postcrash fire. The airplane was being operated as a 14 Code of Federal Regulations Part 91 personal flight. Instrument meteorological conditions existed near the accident site about the time of the accident, and an instrument flight rules flight plan had been filed. The flight originated at Lancaster Airport, Lancaster, Pennsylvania, about 1612, and was destined for Norwood Memorial Airport (OWD), Norwood, Massachusetts.

Review of radar and voice communication data provided by the Federal Aviation Administration (FAA) revealed that the pilot was preparing to conduct an instrument approach procedure for landing at OWD. The flight was about 15 miles from OWD at an altitude of 3,300 ft mean sea level (msl) when the pilot declared an emergency to air traffic control, stating that the airplane was experiencing an "engine problem." The pilot asked the controller about the nearest airport, and the controller provided him with radar vectors to an alternate airport. About 30 seconds later, the pilot advised that he was unable to maintain altitude, and he subsequently stated, "we got a real bad vibration we're losing engine." The controller advised that there was a highway right of the airplane's position and about 2.5 miles away, and the pilot responded, "we have no engine we're [in instrument meteorological conditions] I need help." The controller provided vectors toward the highway, which the pilot acknowledged. Shortly thereafter, the pilot stated, "we're gliding." At this time, radar data showed the airplane about 1,450 ft msl and 2 miles south of the highway. The last recorded radar return, about 40 seconds later, showed the airplane in a right turn about 700 ft msl and at a groundspeed of 66 knots about 0.1 mile from the accident site.

Several witnesses reported hearing an airplane engine making noise and then stopping or going silent. They could not see the airplane due to the low cloud ceiling. One witness, who was located across the street from the accident site, described first hearing a "low moan buzzing sound" and then looking up and seeing the airplane over the trees at the rear of his property with its wings "wagging back and forth." He added that, as it passed over his house, it was flying in a straight line and "wobbling." He then lost sight of it, and shortly after, heard a "boom." Another witness, located adjacent to the accident scene, described hearing what sounded like "a broken fan" before the airplane impacted the house. PERSONNEL INFORMATIONAccording to FAA records, the pilot held a commercial pilot certificate with airplane single-engine land, airplane multiengine land (limited to center thrust), and instrument airplane ratings.

The pilot's logbook was damaged by fire and was not legible. His most recent FAA third-class medical certificate was issued on April 17, 2014, at which time, he reported 1,500 hours of total flight experience. AIRCRAFT INFORMATIONThe six-seat, low-wing airplane was manufactured in 1990 and powered by a Continental IO-550-B6A, 300-horspower, six-cylinder engine driving a three-bladed propeller. The airplane's most recent 100-hour inspection was completed on June 5, 2015, at which time, the airplane had accumulated 2,143 total hours in service and 2,143 total engine hours, 410 hours of which were accumulated since the engine was overhauled in June 2011.

The engine maintenance logs noted that the oil filter was examined for metal particles during the most recent inspection as well as during five of the seven oil changes performed since the engine overhaul, and no metal or debris was found. The engine oil was also sampled and analyzed by a test laboratory three times since overhaul with normal results.

When the engine was overhauled, an overhauled primary alternator and a new parts manufacturer approval (PMA) alternator drive coupling were installed. The alternator was removed and replaced twice in October 2011, at 21 and 23 hours since engine overhaul, respectively. No logbook entries specifically mentioned the alternator drive coupling (a gear assembly installed on the alternator shaft that mates with a gear on the engine crankshaft to turn the alternator). According to a representative from the engine overhaul facility, the serial number of the coupling in service at the time of the accident matched the one that was installed at the time of overhaul. The coupling did not have a specified life limit; however, the instructions for continued airworthiness provided by the coupling manufacturer recommended that it be replaced at engine overhaul. The airplane was also equipped with a standby alternator installed in accordance with a supplemental type certificate. METEOROLOGICAL INFORMATIONThe 1735 recorded weather observation at North Central State Airport (SFZ), Pawtucket, Rhode Island, located about 8 miles southwest of the accident site at an elevation of 440 ft msl, included overcast ceiling at 800 ft above ground level, wind from 010° at 9 knots, visibility 9 statute miles, temperature 14°C, dew point 11°C, and an altimeter setting of 29.70 inches of mercury. AIRPORT INFORMATIONThe six-seat, low-wing airplane was manufactured in 1990 and powered by a Continental IO-550-B6A, 300-horspower, six-cylinder engine driving a three-bladed propeller. The airplane's most recent 100-hour inspection was completed on June 5, 2015, at which time, the airplane had accumulated 2,143 total hours in service and 2,143 total engine hours, 410 hours of which were accumulated since the engine was overhauled in June 2011.

The engine maintenance logs noted that the oil filter was examined for metal particles during the most recent inspection as well as during five of the seven oil changes performed since the engine overhaul, and no metal or debris was found. The engine oil was also sampled and analyzed by a test laboratory three times since overhaul with normal results.

When the engine was overhauled, an overhauled primary alternator and a new parts manufacturer approval (PMA) alternator drive coupling were installed. The alternator was removed and replaced twice in October 2011, at 21 and 23 hours since engine overhaul, respectively. No logbook entries specifically mentioned the alternator drive coupling (a gear assembly installed on the alternator shaft that mates with a gear on the engine crankshaft to turn the alternator). According to a representative from the engine overhaul facility, the serial number of the coupling in service at the time of the accident matched the one that was installed at the time of overhaul. The coupling did not have a specified life limit; however, the instructions for continued airworthiness provided by the coupling manufacturer recommended that it be replaced at engine overhaul. The airplane was also equipped with a standby alternator installed in accordance with a supplemental type certificate. WRECKAGE AND IMPACT INFORMATIONThe airplane impacted the corner of the roof and the backyard deck of a residence and came to rest upright, parallel to and about 15 ft from the rear wall of the home, oriented on a magnetic heading of 320°. The airplane and most of the residence were consumed by postcrash fire.

Flight control continuity was established from the flight control surfaces to the cockpit area; the left rudder cable and the left aileron cable turnbuckle exhibited fractures consistent with overload. The right flap actuator position was consistent with the right wing flap being in the retracted position. The left flap actuator was consumed by fire. The landing gear and actuators were found in the extended position. First responders reported detecting a strong odor of fuel when they arrived on scene.

Examination of the engine revealed that the crankcase was breached over the No. 6 cylinder barrel. Two additional puncture holes were found in line with the No. 1 cylinder connecting rod, located between the left and right magnetos. The oil sump was fractured and partially melted away. Fragments consistent with bearing material, connecting rods, lifters, and crankcase material were found in the oil sump and outside the engine crankcase.

During a follow-up examination of the engine, the alternator drive coupling (also commonly referred to as the alternator clutch, drive hub or clutch gear assembly) was found loose on the alternator shaft with its housing separated into two pieces (see figure 1). The coupling exhibited abnormal wear on the inside of the shaft collar and on the gear teeth. The shaft collar section was separated from the remainder of the housing on the back of the coupling (alternator side), around the circumference of the hole, which also exhibited wear consistent with the coupling rotating on the alternator shaft. Both sides of the thrust washer exhibited abnormal wear. The woodruff key was not found.

Figure 1. Accident alternator and coupling

The face gear that drove the coupling was separated from its crankshaft flange, and all four of the attachment bolts and remnants of their locking tabs were found in the oil sump. A portion of the crankcase adjacent to the face gear was damaged and worn away, consistent with contact from the back side of the face gear ring. Metal particles; bearing, piston, connecting rod, and crankcase fragments; and orange particles consistent with the alternator drive coupling's elastomer were found throughout the engine. Metal and elastomer particles were also found in the oil filter element. Four of the piston connecting rods were found separated from the crankshaft, three of which exhibited thermal discoloration and mechanical damage consistent with lack of lubrication and overheating. The two connecting rods that remained attac...