LAS VEGAS, NV, USA
N512AK
North American NAVION B
The pilot completed a run-up with no malfunctions noted, and was cleared for a left downwind departure. As he was departing from the downwind he felt a vibration on the yoke and was returning to land. About 10 seconds later the vibration on the yoke became violent. An explosion occurred and the cabin reportedly filled with smoke. A second explosion followed and the cowling departed the right side of the aircraft and struck the windshield. The pilot made a landing in a residential area, striking a tree and a vehicle during the landing sequence. Examination of the engine revealed that the No. 3 cylinder had separated from the engine, and the hold down nuts to the No's. 1 and 5 cylinders were hand tight. Review of the maintenance records disclosed no evidence of cylinder removals since the last overhaul in 1982, which was 55 hours prior to the accident.
On August 10, 1997, at 0740 hours Pacific daylight time, a North American Navion B, N512AK, crashed in a residential area while attempting to make an emergency landing at the North Las Vegas, Nevada, airport. The residential area is approximately 1.5 miles away from the airport. The pilot reported flames and smoke in the cockpit to the air traffic control tower. The aircraft was destroyed in the ground collision sequence. The pilot/owner sustained minor injuries, and pilot rated passenger was seriously injured. There was no ensuing postimpact fire, and nobody on the ground was injured. Visual meteorological conditions existed for the local personal flight, and no flight plan was filed. The flight originated from the North Las Vegas airport at 0740. The pilot reported that after his preflight was completed he attained a clearance to taxi to runway 7. He completed the run-up with no malfunctions noted and was cleared for a left downwind departure. He reported that on climbout everything was normal. As he was departing from the downwind he felt a vibration on the yoke. He contacted the tower to inform them of the problem and that he was turning back to land. Approximately 10 seconds later he reported that the vibration on the yoke became violent. The pilot stated that there was an explosion and smoke was present in the cabin. A second explosion followed and the cowling departed the aircraft and struck the windshield. He saw a road and, ". . .made a left turn to line up on [the] road. This is the last I remember." An engine examination was conducted by the Safety Board on August 15, 1997, with technical assistance provided by two airworthiness inspectors from the Federal Aviation Administration (FAA) Las Vegas Flight Standards District Office, and a representative from Textron Lycoming engines. The engine was separated from the firewall, but remained attached to the aircraft. The left side cylinders No's. 2, 4, and 6 showed little damage. The right side of the engine, cylinders No's. 1, 3, and 5 exhibited more damage. The No. 1 cylinder showed ground impact signatures. A push rod tube was bent as well as the rocker box cover. The No. 5 cylinder also showed impact damage less severe than the others. The hold down nuts of the No's. 1 and 5 cylinders were checked for breakaway torque. According to the Lycoming technical representative who performed the work, the hold down nuts were hand tight. The No. 3 cylinder and it's connecting rod was broken off and found at the accident site. No cylinder hold down nuts were found on the studs and through bolts. Cylinder studs found in the 11, 8, and 7 o'clock positions were bent up, bent out, and broken off respectively. The cylinder crankcase through bolt in the 4 o'clock position was broken off. The mounting pad of the No. 3 cylinder had evidence of peening from contact with the cylinder base and the connecting rod. The bottom of the mounting pad, where it was in contact with the crankcase, also showed evidence of peening. The inside of the barrel and the valves appeared to be undamaged. The cylinder skirt had damage to the inside portion. After removal of the oil sump, pieces of the No. 3 piston, piston rings, and the piston pin were recovered. One of the connecting rod bolts was broken in two without necking signatures, but the nut remained attached. The other bolt was intact, but the nut was not attached. The upper portion of the connecting rod showed damage in the piston pin bearing area. The connecting rod bearings showed no evidence of lubrication. The Textron Lycoming representative reported that the No. 3 cylinder appeared to have come off first due to the lack of damage to the inside of the cylinder. This resulted in the piston and piston pin assembly to break off, with the connecting rod bolt overloading, which allowed the connecting rod to come off the crankshaft. No other anomalies were noted with the engine. Flight control continuity could not be established due to the extent of the impact damage. The maintenance records were reviewed and the engine was found to have been overhauled in 1982, 55 operating hours prior to the accident. Subsequent to the engine overhaul in 1982, no entries were noted where the cylinders were removed. The mechanic who was performing the recent maintenance on the engine was interviewed. No evidence of recent cylinder removals not recorded in the logbooks was found.
The separation of the number 3 cylinder due to improper overhaul procedures, and the failure to adequately torque the cylinder hold down nuts and through bolts to specification.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
