NTSB Identification: WPR10FA384
14 CFR Part 91: General Aviation
Accident occurred Thursday, August 05, 2010 in Roche Harbor, WA
Probable Cause Approval Date: 06/20/2011
Aircraft: CESSNA 172, registration: N9730H
Injuries: 2 Minor,1 Uninjured.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The pilot departed from an uphill runway, with 10 to 15 degrees of flaps extended for takeoff, which was contrary to the manufacturer's guidance in the Pilot Operating Handbook (POH). The pilot stated that after liftoff, while trying to achieve and maintain an appropriate airspeed, the airplane encountered a downdraft, and he then heard a “pop” that he believed to be an engine problem. The airplane struck trees and terrain about 1,500 feet from the departure end of the runway, and incurred substantial damage to the wings and fuselage. Two separate post accident examinations, including a brief engine run, did not reveal any anomalies that would have precluded normal engine operation, and propeller cuts to tree limbs at the accident site indicated that the engine was developing power. According to the pilot, he selected the departure direction based on his observation of a windsock nearest the runway threshold. He had flown into the airport about 10 times previously, and was aware the runway sloped uphill and that there were trees about 1,000 feet beyond the departure end.
The lack of an airport wind information recording system precluded determination of the wind conditions at the time of the accident, but calculations based on wind direction and speed information from the three weather observation stations nearest the accident site yielded values that ranged from a 4-knot headwind to an 8-knot tailwind. The POH stated that normal and obstacle clearance takeoffs were to be performed with wing flaps retracted, and specified the use of takeoff flaps only for soft or rough fields. The operator developed checklist used by the pilot did not include any specific guidance on the use of flaps for takeoff. The performance data in the POH did not enable a takeoff distance calculation that accounted for the runway slope or the use of flaps; calculations that used the available POH data indicated that with a tailwind of 8 knots, about 2,000 feet were required to clear a 50-foot obstacle. The accident site terrain elevation was approximately 100 feet higher than the departure threshold, and the trees at the site were approximately 50 feet tall.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot’s failure to attain an adequate climb airspeed due to his use of flaps for takeoff, and his selection of a runway, which resulted in an uphill, and possibly downwind, takeoff and subsequent collision with a known obstacle. Contributing to the accident was the operator's cockpit checklist that did not accurately reflect the manufacturer's takeoff procedures. Full narrative available
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