Aviation Accident Summaries

Aviation Accident Summary WPR15LA101

Belfair, WA, USA

Aircraft #1




The pilot reported that the airplane was at 1,500 ft mean sea level as he was returning to the departure airport when the engine "abruptly quit." When all attempts to restart the engine failed, the pilot chose to land on a gravelly split. During the landing roll, the airplane's small tires sunk into the gravel, which resulted in the airplane nosing over. A postaccident examination of the engine revealed that the crankshaft had fractured adjacent to the aft radius of the No. 3 rod journal. Examination of the crankshaft revealed that it failed due to fatigue cracking that had initiated at locations on either side of a preexisting longitudinal crack. The radius also contained several circumferential cracks, including ones in the region corresponding to the relative location of the fatigue origins of the fracture. Examination also revealed that the No. 3 rod journal had been chromium-plated to regain lost material; however, according to the engine manufacturer, chromium plating on bearing journals was not an approved repair. Although the fatigue did not initiate in the plating, it did start near the edge of the replating in an area likely reworked (ground) following the unapproved plating. The multiple circumferential cracks noted in the radius likely resulted from the repair grinding and may have contributed to the fatigue initiation. A review of the engine logbooks revealed that the engine had been overhauled and subsequently inspected by the "magnaflux method" three times in a 14-month period about 15 years before the accident, during which the extensive cracking would have been present, indicating that the magnaflux inspections of the crankshaft were not effectively performed.

Factual Information

On February 10, 2015, at 1330 Pacific standard time, a Vans RV-7 amateur-built experimental airplane, N513BW, was substantially damaged following a total loss of engine power and subsequent forced landing near Belfair, Washington. The airplane was owned and operated by the airline transport pilot, the sole occupant, who received a minor injury. Visual meteorological conditions prevailed for the local personal flight, which was being conducted in accordance with 14 Code of Federal Regulations Part 91. A flight plan was not filed. The flight had departed the Tacoma Narrows Airport (TIW), Gig Harbor, Washington, about 1315, with the destination being the Bremerton National Airport (PWT), Bremerton, Washington. In a report submitted to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the pilot reported that on the day of the scenic flight, and while he was en route back to PWT at about 1,500 feet mean sea level, "…the engine abruptly quit running." The pilot stated that he then pushed the nose down to maintain airspeed, switched fuel tanks, and turned on the boost pump, and pressed the starter button repeatedly, but the engine would not turn over. The pilot reported that during the descent he continued to try to start the engine; however, as this was unsuccessful he elected to land on a gravelly split. During the landing roll the airplane's small tires sunk into the pea-sized gravel, which resulted in the airplane nosing over onto its back and substantially damaging the rudder. On March 2, 2015, under the supervision of the NTSB IIC and representatives from the Federal Aviation Administration, the engine was examined at the facilities of Avian Aeronautics, Bremerton, Washington. The examination revealed that the crankshaft was fractured adjacent to the aft radius of the #3 cylinder rod journal. The crankshaft was subsequently shipped to the NTSB Materials Laboratory, Washington, D.C., for further examination and analysis. An examination of the failed crankshaft, serial number L-2079-36, by a Senior NTSB Metallurgist revealed that both fracture faces received post fracture rotational damage, and the beach marks and other fracture face marking were visible and consistent with fatigue cracking through about two-thirds of the journal cross section. The fracture markings indicated fatigue initiation had occurred in the vicinity of the aft radius of the journal, with additional fractures confined to the forward fracture face. Additionally, the metallurgist reported that closer magnified optical examinations found a large ratchet mark, which indicated fatigue initiation at two locations near or at the surface of the aft journal radius, however, the exact origin locations could not be determined. A radial metallographic section was cut through the forward fracture face and journal. The section uncovered a cracked bright white layer on the journal surface, which was consistent with electroplated chromium. The plated layer blended smoothly into the journal surface before the journal-to-cheek radius. At its maximum, the plated layer measured 0.0037 inches thick. An engineering representative from Lycoming Engines stated that chromium plating on bearing journals was not an approved repair. Overall, the radius appeared non-uniform with a flattened region near the middle and contained several circumferential cracks, including ones in the region corresponding to the relative location of the fatigue origins of the fracture.The cracks ranged in size from less than 0.002 inch to more than 0.020 inch. Some cracks revealed intergranular features, some were transgranular, and the longer ones show both crack paths. In the least damaged locations, the overall radius measured between 0.1559 inch and 01578 inch. The rod cap and bearing were heavily damaged on the aft side consistent with damage during continued rotation subsequent to the fracture of the crankshaft. As received, the bearing insert was displaced forward in the rod cap with deformation to the locating tab. Contact shadows both within the bolt cut out and on the edge of the insert indicated a previous position further aft in the rod cap. The aft location was consistent with normal placement of the bearing. The undamaged portions of the bearing surface showed minimal wear. The bearing shell was stamped on the outer diameter "SL-13521-M06' and date marked "9-99", indicating a 0.006 inch oversized bearing manufactured in 1999. The bearing size was consistent with the markings on the propeller flange "M006MP", which indicates that the rod and main bearings were all undersized by 0.006 inch. Measurements of all main and rod journals were within specification for 0.006 inch undersize diameters. (Refer to the Materials Laboratory Factual Report, Report No. 15-078, which is located in the public docket for this accident.) As all engine logbooks were not available during the investigation, a partial review of the maintenance records for the engine revealed the following: May 20, 1980: major overhaul performed, with a new crankshaft installed; a serial number was not recorded in the maintenance log entry. Tach times records were 5.99 and 4.99 hours. Also annotated, "Engine logs lost." September 1, 1999: a major overhaul was performed on the engine at a recorded tach time of 90.0 hours. Crankshaft 74251 installed, which was the same number steel stamped on the accident propeller flange. January 7, 2000: a major overhaul was performed at a tach time of 95.0 hours since the most recent overhaul. All non-ferrous metal parts inspected by Zygloe Method. November 1, 2000, major overhaul performed. No tach time noted. All ferrous metal parts inspected by Magnaflux Method. All non-ferrous metal parts inspected by Zygloe Method.

Probable Cause and Findings

A total loss of engine power during cruise flight due to the fatigue failure of the engine crankshaft. Contributing to the accident was the unapproved repair and improper inspection of the engine crankshaft.


Source: NTSB Aviation Accident Database

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