Loss of Control in Flight: Eurocopter AS350 B2, N350ST, accident occurred February 18, 2019 in Eureka, Alaska

Additional Participating Entity:
Federal Aviation Administration / Flight Standards District Office; Anchorage, Alaska

Aviation Accident Final Report - National Transportation Safety Board: https://app.ntsb.gov/pdf

Investigation Docket - National Transportation Safety Board: https://dms.ntsb.gov/pubdms 

https://registry.faa.gov/N350ST

Location: Eureka, AK
Accident Number: GAA19CA139
Date & Time: 02/18/2019, 1455 AKS
Registration: N350ST
Aircraft: AIRBUS A350
Aircraft Damage: Substantial
Defining Event: Loss of control in flight
Injuries: 1 None
Flight Conducted Under: Part 135: Air Taxi & Commuter - Non-scheduled

Analysis 

The helicopter pilot reported that, while transporting snow skiers, he landed on a 20º slope below the mountain peak, where he directed the guide and two skiers to unload with the engine running. The pilot saw loose rocks from the peak above fall into the main rotor disk, and after the skiers were clear of the helicopter, he raised the collective and brought the helicopter to a hover. He added that, while hovering, he did not feel any controllability issues, so he repositioned the helicopter up the mountain about 30 ft and "toed in" to unload additional skiers. After the remaining skiers unloaded, the pilot started flying the helicopter down the mountain so that he could shut down the engine and examine the main rotor blades.

The pilot added that, about 10 seconds later, the helicopter began to shake violently. He initiated a forced landing, but about 150 ft above the trees, the "flight controls became progressively hard to control," and the helicopter pitched up. Immediately, he lowered the nose and collective, and about 30 ft above the snow-covered ground, the main rotor disk struck trees, and the helicopter subsequently impacted terrain.

The helicopter sustained substantial damage to the main rotor blades, fuselage, tailboom, and tail rotor blades.

The director of operations reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operation.

Probable Cause and Findings

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
The pilot's selection of unsuitable terrain for landing on snow-covered mountainous terrain with steep rocks above, which resulted in loose rocks damaging the main rotor blades and the subsequent loss of helicopter controllability.

Findings

Aircraft
Performance/control parameters - Attain/maintain not possible (Cause)

Personnel issues
Decision making/judgment - Pilot (Cause)

Environmental issues
Mountainous/hilly terrain - Decision related to condition (Cause)
Tree(s) - Contributed to outcome

Factual Information

History of Flight

Maneuvering-hover
Miscellaneous/other
Off-field or emergency landing
Loss of control in flight (Defining event)
Collision with terr/obj (non-CFIT)

Pilot Information

Certificate: Flight Instructor; Commercial; Private
Age: 54, Male
Airplane Rating(s): Single-engine Land
Seat Occupied: Unknown
Other Aircraft Rating(s): Helicopter
Restraint Used: 4-point
Instrument Rating(s): Airplane; Helicopter
Second Pilot Present: No
Instructor Rating(s): Helicopter
Toxicology Performed: No
Medical Certification: Class 2 With Waivers/Limitations
Last FAA Medical Exam: 04/30/2018
Occupational Pilot: Yes
Last Flight Review or Equivalent: 02/16/2018
Flight Time:  (Estimated) 6000 hours (Total, all aircraft), 2500 hours (Total, this make and model), 4850 hours (Pilot In Command, all aircraft), 8 hours (Last 90 days, all aircraft), 8 hours (Last 30 days, all aircraft), 3 hours (Last 24 hours, all aircraft)

Aircraft and Owner/Operator Information

Aircraft Make: AIRBUS
Registration: N350ST
Model/Series: A350 B2
Aircraft Category: Helicopter
Year of Manufacture: 1993
Amateur Built: No
Airworthiness Certificate: Normal
Serial Number: 2789
Landing Gear Type: Skid
Seats: 6
Date/Type of Last Inspection: 02/09/2019, Annual
Certified Max Gross Wt.: 4960 lbs
Time Since Last Inspection:
Engines: 1 Turbo Shaft
Airframe Total Time: 7085.2 Hours
Engine Manufacturer: Honyewell
ELT: C126 installed, not activated
Engine Model/Series: LTS-101-700D
Registered Owner: Rota Aviation Consulting Llc
Rated Power: 732 hp
Operator: Rota Aviation Consulting Llc
Operating Certificate(s) Held:  Agricultural Aircraft (137); Rotorcraft External Load (133); On-demand Air Taxi (135)
Operator Does Business As: RAVCO
Operator Designator Code: 7RVA 

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual Conditions
Condition of Light: Day
Observation Facility, Elevation: PAAQ, 230 ft msl
Distance from Accident Site: 57 Nautical Miles
Observation Time: 2053 UTC
Direction from Accident Site: 260°
Lowest Cloud Condition:
Visibility:  10 Miles
Lowest Ceiling: Overcast / 4400 ft agl
Visibility (RVR):
Wind Speed/Gusts: 14 knots /
Turbulence Type Forecast/Actual: None / None
Wind Direction: 350°
Turbulence Severity Forecast/Actual: N/A / N/A
Altimeter Setting: 29.67 inches Hg
Temperature/Dew Point: 1°C / -2°C
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: Sutton, AK
Type of Flight Plan Filed: None
Destination: Sutton, AK
Type of Clearance:None 
Departure Time:1215 AKS 
Type of Airspace: Class G

Wreckage and Impact Information

Crew Injuries: 1 None
Aircraft Damage: Substantial
Passenger Injuries: N/A
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries:1 None 
Latitude, Longitude: 61.774167, -147.123333 (est)