NTSB Identification: LAX05LA042.
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Accident occurred Sunday, November 28, 2004 in Big Pine, CA
Probable Cause Approval Date: 02/28/2006
Aircraft: Piper PA-22-108, registration: N4913Z
Injuries: 1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The main landing gear sheared from the airplane during a forced landing on rough, desert terrain. When the pilot was about 30 nautical miles from his destination, the oil pressure needle was pegged on the high side of the indicator. He closed the throttle, and the oil pressure appeared to return to normal. Then, the oil pressure needle fell to zero and the oil temperature began to rise. He prepared to land on a road; however, on short final he could not maintain directional control and alignment with the road due to a crosswind condition. He turned the airplane into the wind and landed in a desert field. Post accident examination revealed that the main crankshaft seal was extruded outward and oil was pumped out during the flight. Approximately 1.5 quarts of oil were drained from the engine prior to its teardown. The engine manufacturer's representative examined the engine crankcase, crankshaft nose seal, and breather tube on January 24, 2005. The seal bore exhibited witness marks indicating that the seal had been occupying the bore properly. In addition, the corresponding witness marks on the crankshaft where the seal had been in contact indicated that the seal had been positioned correctly. The engine breather tube extended from the firewall area, aft to the trailing edge of the right main landing gear strut, which was inconsistent with breather tube length. The breather tube did not have a whistle slot installed. The airplane was originally a show airplane. The breather tube was designed to drain in a way that would prevent oil and moisture from draining onto the airplane. However, due to its nonstandard design, the end of the tube was susceptible to icing. An edition of the Lycoming Flyer stated the following, in part: "Under very cold conditions, this moisture may freeze and continue a buildup of ice until the tube is completely blocked. It is normal practice for the airframe manufacturer to provide some means of preventing freeze-up of the crankcase breather tube. The breather tube may be insulated, it may be designed so the end is located in a hot area, it may be equipped with an electric heater, or it may incorporate a hole, notch or slot which is often called a "whistle slot." When a breather tube with whistle slot is changed, the new tube must be of the same design."
The National Transportation Safety Board determines the probable cause(s) of this accident to be: oil exhaustion due to an improper oil breather tube installation, which became plugged in flight due to frozen moisture build-up. The blocked breather tube then created a crankcase over pressure that caused a failure of the crankshaft seal. The rough, uneven terrain and strong crosswind were factors in the accident. Full narrative available
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