NTSB Identification: LAX05LA160.
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Accident occurred Saturday, May 07, 2005 in Grand Canyon, AZ
Probable Cause Approval Date: 02/28/2006
Aircraft: Cessna 172RG, registration: N4970V
Injuries: 3 Minor.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
During an attempted takeoff, the airplane settled back to the ground and impacted a field about 1 mile south of the airport. The pilot reported that prior to the flight he performed performance calculations for the airplane to ensure that it was capable of departing the higher altitude airport. Performance calculations indicated that with the gross weight near the specified maximum, the airplane would need about 4,500 feet to take off. Prior to departure, the pilot configured the airplane with the flaps retracted and the mixture control in the full forward (rich) position. The Safety Board calculated gross weight of the airplane was 2,767 pounds (117 pounds over the airplane's maximum certified gross weight of 2,650 pounds). The pilot reported that his instructor told him to use an airplane empty weight of 1,624 pounds in his calculations, which the instructor said was typical for the airplane type and could be used for this specific airplane. Using this weight, the airplane would still have been 47 pounds in excess of the maximum gross weight. Performance calculations using the Pilot Operating Handbook (POH) for the airplane indicated a ground roll of 3,118 feet (zero wind 3,464 feet) and the distance to clear a 50- foot obstacle was 3,741 feet (zero wind 4,157 feet) with a predicted 327 feet per minute rate of climb. The POH notes that prior to takeoff from fields above 3,000 feet elevation, the mixture should be leaned to give maximum power in a full throttle, static run-up. The runway the pilot attempted to depart from was 8,999 feet in length with an elevation of 6,609 feet mean sea level (msl). The density altitude was calculated to be 7,728 feet msl. Following the accident, the spark plugs were removed and were black and sooty, an indication that the engine was running rich. The engine was then test-run with no operational anomalies noted.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the pilot-in-command's failure to properly lean the mixture, which resulted in a power deficiency, a degraded climb capability, and the inability to attain/maintain an adequate airspeed that led to a stall/mush condition while departing during high density altitude conditions. Also causal, was the pilot-in-command's inaccurate preflight performance and weight and balance calculations. Full narrative available
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