NTSB Identification: ANC12FA014
Scheduled 14 CFR Part 135: Air Taxi & Commuter
Accident occurred Thursday, December 15, 2011 in Nanwalek, AK
Probable Cause Approval Date: 10/29/2013
Aircraft: CESSNA U206G, registration: N252AL
Injuries: 4 Minor.
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 commercial pilot was taking off on the third leg of a scheduled flight returning to the airplane’s base of operation. Earlier in the day, the weather in the area was not suitable for flight operations, but the pilot, along with another company pilot, performed the company risk assessment and decided that, under the current conditions, flights could depart. The pilot reported that the first two legs were uneventful. However, he noted that, upon landing at the end of the second leg, about 3 inches of slush covered the runway, with as much as 6 inches in some areas, and that the wind was from the east at 12 to 15 knots.
After loading passengers, the pilot decided to taxi from the north parking ramp to the opposite end of the runway for a northerly departure. The pilot and witnesses stated that the airplane’s takeoff performance was degraded due to the runway contamination, but the airplane was still able to lift off just past the midfield point. The pilot stated that after the airplane lifted off in a nose-high attitude, he immediately started a shallow left turn to avoid the rising terrain at the north end of the runway. He said that after the airplane cleared a retaining wall on the west side of the runway, it encountered a downdraft, and the pilot was unable to maintain a climb. The airplane impacted the ocean about 100 yards offshore.
There is no official weather reporting at the airport. About 35 minutes before the accident, the nearest official weather reporting station, located 9 nautical miles northeast of the airport, reported wind from 170 degrees at 3 knots. About 10 minutes after the accident, it reported wind from 170 degrees at 10 knots, gusting to 15 knots. The airport is tightly constrained on both sides by terrain and water, and the runway condition is difficult to maintain due to sea erosion and lack of suitable maintenance equipment. According to the airport manager, there is a contract maintenance provider in the village, and, on the morning of the accident, it was determined that runway conditions did not require maintenance. The contractor stated that the weather was very dynamic that day; he asked the pilot of the first airplane that landed if any maintenance was required on the runway and was told that the runway was fine. However, given the contamination on the runway, the accident pilot likely lifted off farther down the runway than normal. The airplane’s attitude and slow airspeed, combined with the unfavorable wind conditions he encountered after he executed the shallow turn, likely resulted in an aerodynamic stall.
A review of the operator’s flight risk assessment form showed that, for the conditions during the accident flight, the pilot and another company pilot should have assigned three of the five risk areas a value that requires additional management approval before flights could be released. Instead, they agreed that conditions were appropriate for flight and were allowed to exercise operational control to release the flights for departure, which placed the flight at risk for an accident.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot’s decision to takeoff from a contaminated runway with unfavorable wind conditions, and his failure to maintain airspeed during the initial climb, which resulted in an aerodynamic stall. Contributing to the accident was the operator’s inadequate procedures for operational control and dispatch. Full narrative available
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