Big Pine, CA, USA
N4913Z
Piper PA-22-108
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."
On November 28, 2004, about 1040 Pacific standard time, a Piper PA-22-108, N4913Z, encountered rough terrain and sheared off the landing gear during a forced landing in the Death Valley National Park, approximately 24 nautical miles northeast of Big Pine, California. The commercial pilot, also the registered owner, was operating the airplane under the provisions of 14 CFR Part 91. The pilot was not injured; the airplane sustained substantial damage. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot departed the Bullhead City International Airport, Bullhead City, Arizona, about 0800. The pilot's final destination was the Napa County Airport, Napa, California, and he was planning an en route fuel stop at the Eastern Sierra Regional Airport, Bishop, California. According to the pilot, when he was about 30 miles from Bishop, 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. The pilot reset his transponder to 7700 and tuned his radio frequency to 121.5. He prepared to land on a road; however, on short final he could not apply control pressures that would overcome the crosswind condition. He turned the airplane into the wind and landed in a rough desert field. The main landing gear sheared from the airplane during the landing sequence. The engine was torn down at Performance Aero on January 5, 2005. The aviation maintenance technician reported 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. Post accident teardown did not reveal any other operational anomalies, and there were no indications of a metal component failure throughout the engine. The technician further reported that during flight, the crankshaft case breather tube can become obstructed by ice or other debris. When this occurs, a back pressure forms, which may result in an extrusion of the seal. 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 crankcase breather tube ran from a neoprene tube positioned at the lower left corner of the firewall, aft to the trailing edge of the right main gear strut. When the representative blew air through the tube, water came out of the tube. The aluminum breather tube that ran from the engine to the neoprene tube was absent of the whistle slot. According to the pilot, prior to his purchase, the airplane was a show airplane. The breather tube was designed to drain in a way that would prevent oil and moisture from draining onto the airplane. A review of the maintenance records for the airplane did not reveal when the modification was completed. An excerpt from an edition entitled "The Whistle Slot," of the Lycoming Flyer, a publication produced by Textron Lycoming, states the following: "Moisture is expelled from the engine crankcase through the breather tube which often extends through the bottom of the engine cowling into the air stream. 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." The operator of any aircraft should know which method is used for preventing freezing of the breather tube, and should insure that the configuration is maintained as specified by the airframe manufacturer. Because of its simplicity, the "whistle slot" is often used. Although the end of the tube may extend into the air stream, a notch or hole in the tube is located in a warm area near the engine where freezing is extremely unlikely. When a breather tube with whistle slot is changed, the new tube must be of the same design."
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.
Source: NTSB Aviation Accident Database
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