South Lake Tahoe, CA, USA
N51172
CESSNA 150
Witnesses stated that the airplane lifted off and climbed to about 100 feet above the runway in an unusually high nose-up pitch attitude before turning left and descending into terrain. The pilot transmitted a "mayday" call on the Common Traffic Advisory Frequency just before the airplane entered the left turn. During postaccident testing of the engine, excessive vibration occurred as the rpm increased, and one of the spark plugs became excessively sooty, indicating an overly rich fuel/air mixture. The carburetor was then replaced and the engine ran normally at all power test points; the previously sooty spark plug was normal after this test. The accident carburetor was then examined, and a pin that secures the carburetor’s metal floats to their pivot point in the carburetor bowl was missing. Marks indicating contact on the edge of a float and on the side of the bowl were found, indicative of rubbing interference with the side of the bowl. The float-to-bowl contact likely altered the fuel quantity in the bowl, which likely created an overly rich mixture that would have further reduced available engine power at the high density altitude at which the airplane was being operated. The density altitude was calculated to be 8,708 feet. High density altitude adversely affects airplane climb performance and requires pilot vigilance to maintain adequate airspeed during takeoff and climb.
History of Flight On July 5, 2009, about 1301 Pacific daylight time, a Cessna 150J, N51172, owned and operated by a private individual, experienced a loss of control during initial climb from the Lake Tahoe Airport, South Lake Tahoe, California. Seconds after lifting off from runway 18, the airplane entered an uncontrolled descent and impacted terrain adjacent to the airport. Visual meteorological conditions prevailed at the time of the personal flight, and no flight plan had been filed. The airplane was substantially damaged, and the private pilot was fatally injured. The flight was performed under the provisions of 14 Code of Federal Regulations Part 91, and it was originating at the time of the accident. According to a witness who was preparing to depart on runway 18, the accident airplane accelerated on the runway's centerline, became airborne, and climbed an estimated 100 feet above the runway. During this time the airplane was in an unusually high nose up pitch attitude. No evidence of smoke was observed trailing from the airplane. The accident airplane turned left and appeared to enter a left spin as it rapidly descended from his view. The witness also reported hearing the accident pilot broadcast a "mayday" call seconds prior to the crash. Two other witnesses were interviewed by responding El Dorado County Sheriff deputies. The witnesses were on the airport and their statements were consistent with the witness who was preparing to depart. One witness said the airplane had completed a 90 degree left turn before it entered a nose down turning descent to ground impact. The second witness thought the airplane had completed more of a turn before the descent. Pilot Information Review of Federal Aviation Administration (FAA) airman and medical records for the 41 year old pilot disclosed that he held a private pilot certificate with ratings for airplane single engine land and instrument airplane, the last issuance of which was dated April 25, 2001, when the instrument rating was added to his certificate. The original issuance of the private pilot certificate was dated June 25, 1999. The most recent medical certificate, a second class medical, was issued on July 26, 2005, and contained the limitation that correcting lenses be worn while exercising the privileges of the certificate. No recent personal flight records were found. On the last airman medical application in July of 2005, the pilot reported a total flight time of 430 hours, with 50 hours flown in the last six months. On the medical application immediately prior to the July 2005 and dated May of 2002, the pilot reported a total time of 425 hours, with 25 flown in the last six months. Aircraft Information The pilot purchased the airplane about 2 months prior to the accident flight. The airplane’s maintenance records indicated that the airplane was maintained on an annual inspection basis. On May 25, 2007, at an airplane total time of 6,092.45 hours, the airplane received an annual inspection. A notation in the aircraft’s logbook indicated that this inspection involved, in part, installation of a carburetor that had been overhauled by Central Cylinder Service, Inc., Omaha, Nebraska. A maintenance release tag stapled to the logbook indicated that the previous week, on May 18, 2007, the carburetor had been overhauled and tested by Central Cylinder Service, Inc. The carburetor was listed as being Model MA-3SPA, bearing serial number BE 74-9525. The next annual inspection was due to be performed by May 31, 2008. Maintenance records indicated that on May 31, 2008, the airplane’s recording engine tachometer registered 3,212.98 hours. On June 17, 2008, the tachometer registered 3,233.82 hours. On July 16, 2008, the tachometer registered 3,269.20 hours. On August 5, 2008, the tachometer registered 3,298.03 hours, and on October 9, 2008, the tachometer registered 3,361.95 hours. The aircraft’s logbook additionally indicated that the next annual inspection was performed on November 17, 2008, at an engine tachometer time of 3,362 hours, and at a total airplane time of 6,509.67 hours. No additional evidence of the carburetor having been removed from the airplane or serviced was listed in the maintenance logbooks. By the accident date, the carburetor had been in use about 491 hours following its overhaul. The airplane’s original Continental engine, model O-200-A, serial number 251609, was removed, overhauled, and reinstalled in the airplane. Also, the engine’s recording tachometer had been replaced several times. On the accident date, the engine’s approximate total time was 4,809 hours, and the airplane’s total time was about 6,583.6 hours. The airplane had been operated about 73.9 hours since receiving its last annual inspection. The last maintenance on the engine (oil change) was performed on May 20, 2009. The last maintenance on the airframe (replacement of landing and navigation lights, and fuel strainer O-rings) was performed on May 22, 2009 Meteorological Information The South Lake Tahoe airport METAR observation at 1253 reported clear skies with 10 miles visibility. The temperature and dew point were noted as 79 degrees Fahrenheit (26 Centigrade) and 27 (-3 Centigrade) and the winds were recorded as 200 degrees at 11 with higher gusts to 20. The altimeter setting was 30.19. Based on the airport elevation and the weather observation, the density altitude was calculated to be 8,708 feet. Airport Information The South Lake Tahoe airport is located in a mountain valley at an elevation of 6,264 feet, with a large lake to the north and a narrowing valley to the south. The mountain peaks and ridges that surround the valley rise to elevations in excess of 9,900 feet MSL. It has one asphalt covered runway oriented north and south. Runway 18 - 36 is 8,544 feet long by 150 feet wide. The Airport Facility Directory notes that the preferred arrival runway is 18 and runway 36 is preferred for departures. Wreckage and Impact Information The accident site was in a level mountain meadow on U.S. Forest Service land just east of and adjacent to the airport's runway. The ground was covered in moderate height grass and scrub brush up to 5 feet high. A ground scar was noted about 50 feet in front of the airplane with fragmented elements of the left fiberglass wing tip located in the disturbance. The engine was crushed backwards into the firewall, with rotational crush deformation noted to the spinner. The forward fuselage was at a 45-degree angle to the ground, with lower forward fuselage crush folds consistent with that angle. Both wings exhibit leading edge crush deformation, with the accordion folds oriented about 45 degrees to the longitudinal axis. The crush damage to the left wing extends outboard and aft at a 30-degree angle from the mid span point. The rearward crush damage to the right wing extended from the cabin to the wing tip, with the most outboard 4 feet bent upwards at a 20-degree angle. The empennage was buckled at the rear baggage bulkhead and bent downward and rotationally displaced to the right. The empennage fixed and movable control surfaces remained attached to their hanger and hinge assemblies. With the exception of the rudder, control system continuity was established from the cockpit controls to the control surfaces. Rudder cable continuity was present from just below the pilot’s seat to the rudder bell cranks; the cables were trapped in skin and structure crush folds from the point under the pilot’s seat to the rudder pedals. The fuel selector was found in the “ON” position. Approximately 12 gallons of blue colored liquid with an odor reminiscent of 100 low lead aviation gasoline was drained from the fuel tanks. The gascolator bowl was intact and fuel was present in the bowl, with some sediment found in the bottom of the container along with about 1 ounce of water. The fuel screen was clear. The carburetor was intact. About 2 to 3 ounces of blue colored fuel was found in the bowl and no contaminants or water was observed. The finger screen was clear. Metal floats were noted in the bowl. The accelerator pump appeared to be functional and sprayed fuel. The McCauley 1A101 model propeller remained attached to the crankshaft flange. One blade exhibited “S” bending, with leading edge damage and trailing edge scratches. The second blade was bent forward about 10 degrees and also exhibited leading edge damage and trailing edge scratches Medical and Pathological Information The pilot sustained fatal injuries in the accident sequence and an autopsy was arranged by the El Dorado County Sheriff-Coroner. The cause of death was listed as blunt force traumatic injury. Tissue and fluid samples were submitted to the FAA Civil Aeromedical Institute for toxicological analysis. The results were negative for alcohol and all screened drug substances. Tests and Research Between July 23 and 24, 2009, the accident engine from the referenced airplane was examined at TCM's Mobile, Alabama, manufacturing facilities. The examination was performed while under the supervision of the below-listed National Transportation Safety Board investigator. In summary, the engine was initially examined in its "as received" condition. In preparation for the test run, several components were replaced after noting that they were too impact-damaged to be functionally tested. These components included the magneto wiring harness assembly (broken leads), the carburetor air filter box and exhaust manifold (crushed). Additional components that were observed either impact damaged or whose functionality was deemed unnecessary to the engine's operational evaluation, were also removed from the engine. All of the accident spark plugs were removed from the engine. A serviceable set of exemplar spark plugs were inserted into each cylinder for the first test run. The engine was placed into TCM's test cell and was started without difficulty. Measurements of the engine's operational performance were recorded. The engine was run up to about 2,000 revolutions per minute (rpm), which was achieved when the throttle was advanced to about the 3/4-open position. As the rpm accelerated, a pronounced vibration was noted. The frequency of the vibration increased as the rpm increased. Also, the engine's sound exhibited an increased roughness with increasing rpm. When the throttle was increased beyond about 3/4-throttle, the engine began losing rpm. As the throttle was further advanced toward the full throttle position, the engine's rpm decreased. Thereafter, the test run was terminated, and the engine was stopped. The accident carburetor was removed and was replaced with an exemplar carburetor. The exemplar spark plugs were removed and inspected. The exemplar spark plugs were compared to the pictures published in the "Champion Aviation Check-A-Plug" diagram #AV-27" for massive electrode plugs. The appearance of the #4 upper plug was consistent with the "Carbon Fouled" picture. It had black, sooty, deposits on the electrode and over the face of the threaded barrel. The other plugs exhibited an appearance consistent with the "Normal" service diagram. Then, the accident carburetor was removed from the engine and an exemplar serviceable carburetor was installed in place of the accident carburetor. The exemplar spark plugs were reinserted into the cylinders, and the engine was started. The engine operated in accordance with TCM's design specifications up to the full power setting at 2,650 rpm. All test parameters were met and the engine's performance output was consistent with the engine's type certificate. The upper plugs were then removed and reinspected. The #4 upper plug, that was previously observed carbon fouled (sooty), appeared normal. The remaining plugs were removed and inspected. All appeared with normal combustion signatures. The accident plugs were reinserted into the engine and the engine was run up to about 2,600 rpm. After about 3 minutes of operation, the engine was shut down and the plugs were reexamined. The black sooty #4 plug, along with the other plugs exhibited normal combustion signatures. The accident carburetor was disassembled. A pin, which secures its metal floats to their pivot point in the bowl, was missing. Marks indicative of rubbing interference were present on the edge of a float and on the side of the bowl.
A partial loss of engine power due to a malfunctioning carburetor and the pilot’s failure to maintain adequate airspeed while maneuvering to return to the runway. Contributing to the accident was the high density altitude.
Source: NTSB Aviation Accident Database
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