Pilot Debrief

Piper PA-31-350 near Cooper Landing, AK — 2019-11-30

Final reportANC20FA007
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Date
2019-11-30
Location
Cooper Landing, AK, USA
Aircraft
Piper PA-31-350
Registration
N4087G
Category
Airplane
Highest injury
Fatal
Fatalities
3
Phase of flight
Descent

Probable cause

The pilot’s failure to maintain clearance from terrain during gusty wind and reduced visibility night conditions.

NTSB narrative

Emergency clinic personnel contacted multiple air ambulance companies prior to contacting the accident operator, requesting air ambulance transportation of a patient. The first company contacted turned down the flight due to limited daylight hours. The second company declined the flight due to poor weather conditions. After accepting the flight, the pilot departed at night, destined for an airport about 75 nautical miles away. The route of flight would take the flight across a peninsula and a mountain range. The destination airport was at the north end of a fjord surrounded by mountains ranging from 4,000 ft to 6,000 ft elevation; for this reason, the destination airport prohibited instrument approaches at night. Radar data indicated the accident airplane departed and flew south about 3,000 ft mean sea level (msl) toward a highway. The airplane then descended to 2,200 ft msl while flying a right racetrack pattern before flying into a valley. The last data point indicated the airplane was over the west end of a lake at 2,100 ft msl, on a 127° course, and 122 kts groundspeed. Witnesses reported that they saw the lights of the airplane flying over the highway that night. One witness stated that he saw the airplane west of the mountains turn in a circle as it descended and then entered the valley. Another witness reported seeing the airplane flying low before it impacted the mountain and a post-crash fire ensued. The airplane impacted the mountain at an elevation of about 1,425 ft msl in an area of steep, heavily tree-covered terrain near the southeast end of a lake. The airplane was highly fragmented and burned; however, all major airplane components were accounted for at the accident site. Postaccident examination of the engine revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. Weather simulations conducted after the accident indicated east to southeast winds above the accident site with wind speeds between 30 to 50 knots, downdrafts and updrafts with magnitudes of +/- 1,500 fpm, and relative humidity values above 90% at the mountain tops. Witness reports corroborated this information and also described precipitation and mountain obscuration. Airman's Meteorological Information (AIRMET) reports were active for the accident region that warned pilots of low-level wind shear (LLWS) conditions, moderate icing conditions between 6,000 and 15,000 ft, and occasional instrument flight rules (IFR) and mountain obscuration conditions due to precipitation and clouds. Weather graphics valid at the accident time and before the departure of the accident flight showed IFR conditions along the route of flight, isolated moderate turbulence conditions in LLWS, and moderate icing above 6,000 ft. It is likely the airplane encountered strong mountain wave conditions while traveling across the peninsula and through the end of the accident flight. Additionally, the terrain was likely obscured due to the reduced visibility, clouds, light rain or drizzle and the pilot likely did not see the rising terrain as he flew in the valley toward the destination. While sufficient weather information was available to predict the windy conditions and mountain obscuration for the flight, it is unknown what information the pilot had regarding the weather prior to departure.

Analysis

Primary failure mode
Controlled flight into terrain
First missed decision gate
Pilot could have aborted the flight due to deteriorating weather conditions.

NTSB coding

Evidence available

  • Photos
  • 25 docket documents
View NTSB final reportView NTSB docket

Docket documents25

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