POULSBO, WA, USA
N700RM
Modrow AVID FLYER
The Rotax engine in the amateur-built airplane seized while in flight. The pilot performed an emergency landing, with the airplane sustaining substantial damage. NTSB examination of the crankshaft, bearings and rods, and associated componentry, found no evidence of a general lack of lubrication. The labyrinth sleeve, located between the two front (PTO, or power takeoff end) bearings showed evidence of circular scoring and material transfer contact between the bore of the sleeve and the crankshaft surface, similar to that which would occur with foreign matter in the clearance space between the sleeve and crankshaft. A portion of what appeared to be a melted bearing retainer ring was found in one bearing. The flat face on the magneto side of the labyrinth sleeve was darkened and contained foreign material deposits which appeared similar in color and nature to the material of the bearing retainer ring. The PTO side of the labyrinth sleeve was configured with a ring at the inner and outer diameters, with a hollowed out region in between. The hollow contained foreign material deposits, as did the surface of the inner diameter ring. Little discoloration was noted on the PTO side of the labyrinth sleeve. The bore of the labyrinth ring showed a large amount of circumferential scoring and material transfer. The corresponding area on the surface of the crankshaft contained similar scoring and material transfer, consistent with contact between these two surfaces. The ball bearings in both of the PTO bearing assemblies were unevenly spaced, indicating that their retainer rings were either lost or somehow ineffective in keeping the balls evenly spaced.
On June 22, 1999, at 1703 Pacific daylight time, an amateur-built Modrow Avid Flyer, N700RM, sustained substantial damage during a forced landing after a power loss, near Poulsbo, Washington. The private pilot, the sole occupant, sustained minor injuries. Visual meteorological conditions prevailed for the local flight, which had departed Bremerton, Washington. There was no fire, and no report of an ELT actuating. A sheriff's deputy spoke with the pilot before he was transported to the hospital. The deputy said that the pilot had stated that the engine was losing rpm and he had attempted a forced landing. The airplane impacted nose down in a soft, open field. The deputy observed fuel in both fuel tanks, and noted that the fuel selector was in the on position. In a written statement, the pilot stated that while flying at approximately 800 feet, the tachometer indicated a drop of several hundred rpm. He headed for the closest open field and attempted to gain altitude while trying to diagnose the problem. All engine instruments indicated normal (EGT, water temperature and oil pressure). He stated that "the engine abruptly stopped with the prop stationary. An attempt was made to restart the engine with the electric starter but the engine remained seized." The pilot attempted an approach to the open field below. He stated that "in a low right turn maneuver to miss a fence, the airspeed dropped below stall and the plane nosed down into the marsh. The left wing struck the ground and the plane did a 180 degree ground loop around the left wing and remained upright." NTSB Materials Laboratory performed an examination of the Rotax engine crankshaft, bearings, and rods. One bearing, oil seal, polymeric bearing retainer ring, and a labyrinth sleeve had been removed from the power takeoff (PTO) end of the crankshaft prior to submission the laboratory. All bearings and connecting rods remaining on the crankshaft, except for the bearings on the crankshaft forward of the PTO crankblade, rotated freely when manipulated by hand and their bearing surfaces showed evidence of lubrication and did not appear discolored. The bearing remaining on the PTO end of the crankshaft was slightly browned on the external surface of the outer race, consistent with heating of the component. The outer race moved slightly when manipulated, but the movement was restricted by the ball bearings, which had been flattened and were no longer free to rotate. The ball bearings showed surface irregularities indicative of melting and resolidification, also consistent with a heating of the bearing. This bearing was not removed from the crankshaft. The previously removed bearing was found to be badly browned on all of its exterior surfaces, and a dried substance was noted on the interior of the bearing. This dried substance appeared consistent with heated lubricant material. No damage was noted on the oil seal. The bearing retainer ring was intact, but showed evidence of partial melting. The ball bearings in both the remaining PTO end bearing and the removed bearing assembly were unevenly spaced, indicating that the retainer ring was either lost or somehow ineffective in keeping the balls equally spaced. A portion of what appeared to be a melted bearing retainer ring was found in the bearing that was removed. This portion of a retainer ring did not appear to mate with or be a part of the intact bearing retainer ring. The flat face on the magneto side of the labyrinth sleeve was darkened and contained foreign material deposits which appeared similar in color and nature to the material of the bearing retainer ring. The PTO side of the labyrinth sleeve was configured with a ring at the inner and outer diameters, with a hollowed out region in between. The hollow contained foreign material deposits, as did the surface of the inner diameter ring. Little discoloration was noted on the PTO side of the labyrinth sleeve. The bore of the labyrinth ring showed a large amount of circumferential scoring and material transfer (refer to illustrations in attached report). The corresponding area on the surface of the crankshaft contained similar scoring and material transfer, consistent with contact between these two surfaces. The engine had been overhauled by the owner and the airplane returned to service on June 18, 1999. The engine had three hours operating time since overhaul, at the time of the accident.
Engine seizing due to failure of main bearing assemblies. Factors include foreign material in the labyrinth sleeve, and a stall encountered while the pilot was attempting his emergency landing.
Source: NTSB Aviation Accident Database
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