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On July 14, 2007, about 1130 Pacific daylight time, a homebuilt Clement Zenith Zodiac CH601 HDS, N239PC, experienced a loss of engine power and descended into a single family residence near Rosamond Skypark Airport, Rosamond, California. The airplane and a portion of the private residence sustained substantial damage. The private pilot, the sole occupant, sustained minor injuries; there were no injuries to people on the ground. The pilot was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The local personal flight departed from Rosamond about 1030.
In a written statement, the pilot reported that he completed building the accident kit airplane in December 2006, after 6 years in process. Prior to the accident, he had started the engine on 11 occasions and had amassed about 2 hours of operational time, which was accumulated with the airplane on the ground, mostly during taxi tests. The accident flight was the airplane's maiden flight, where the pilot planned to complete a series of performance tests.
The pilot further stated that after departure, he flew the airplane to 6,500 feet mean sea level (msl). He performed his predetermined maneuvers, which encompassed mostly shallow banks, but also included four simulated approaches to landing. Thereafter, he descended the airplane to the traffic pattern altitude (about 3,400 msl) and entered the downwind leg for runway 25. As he maneuvered onto the base leg, he reduced the engine power from about 4,500 rpm to 2,000 rpm. The airplane began to lose a significant amount of altitude, and in response, the pilot manipulated the throttle control forward in an effort to increase the engine rpm. The engine then experienced a total loss of power. The airplane descended and impacted the roof of a private residence where it came to rest inverted. The pilot opined that he had reduced power too much.
TESTS AND RESEARCH
Following the accident, National Transportation Safety Board investigators examined the wreckage at the facilities of Aircraft Recovery Services, Pearblossom, California.
Investigators established control continuity of all control surfaces. The left aileron/flap control arm was previously detached by recovery personnel.
The three-bladed controllable pitch propeller IVOPROP remained attached to the engine. All blades were fragmented with two blades split in the middle. The propeller was removed revealing that all the pitch change links were intact.
According to the data plate affixed to the crankcase, the powerplant of the accident airplane was a Rotax 912UL, serial number 4405652. Throughout the examination, the engine was identified and referenced in accordance with Rotax standardization consisting of the number 1 and 3 cylinder in the forward and aft right side of the engine, respectively (perspective from the pilot position); the number 2 and 4 cylinders were referenced in the left forward and aft position, respectively.
An external examination was performed of the engine and accompanying accessories. The engine was attached to the fuselage and appeared intact. Visual examination revealed that the left Bing carburetor was not attached to the intake manifold. The radiator was crushed and leaking fluid, which appeared to be a result of impact damage. The oil sump contained oil, which measured just below the low indication of the dipstick. The battery was broken from the mounts. A film of oil was on the bottom cowling.
Removal of the upper spark plugs revealed that they were all a similar black coloration, which is an indication of a rich fuel/air mixture according to the Champion Check-A-Plug Comparison Chart. The number 4 spark plug was loosely affixed in its respective bore and noticeably finger tight. Upon rotation of the crankshaft, investigators established valve train continuity and obtained thumb compression in all cylinders. The choke cables from the cockpit to the carburetors were frayed, consistent with it making repetitive wear with the outer sleeve.
The right carburetor bowl was removed revealing a small trace of fluid (about a teaspoon), which was brown in color and similar in color to a maple syrup; the odor was consistent with a varnished fuel. The left carburetor bowl contained a small amount of fluid that was similar to that of the fluid found in the right carburetor, though a shade lighter in color. The carburetor bowls were clean from debris. The fuel found in the center fuel tank was similar to that found in the carburetor bowls.
A dark black residue (coating) was found lining the tail pipe exhaust.
The airplane was strapped to a forklift and the left carburetor was secured to the intake. Investigators added oil and fuel and attempted to run the engine. The engine started utilizing normal starting procedures and the oil pressure was observed to stay within the normal operating range. The throttle control was manipulated and the engine responded respective to the command motion. The engine emitted a thick white smoke during operation from the exhaust. The highest rpm obtained was in excess of 4,000 rpm.
Investigators noted that when retarding the throttle toward the idle position, the throttle arms did not move against the idle adjustment screws (stops). Manual manipulation of both throttle arms to the carburetors' adjustment screw resulted in the engine experiencing a loss of power. The same action (moving the throttle arms to their respective stops) was repeated four times, producing the same results. The muffler was removed and found to have about 2 ounces of oil inside. The engine did not emit the smoke following the removal of the muffler.