Accident Overview
On June 24, 2008, at approximately 1345 mountain daylight time, a Schweizer 269C helicopter, registered as N432MS, collided with terrain during takeoff near Buffalo, Wyoming. The helicopter was operated by Northern Skies Aviation, Inc., under 14 Code of Federal Regulations Part 135. The certificated airline transport pilot and the passenger were not injured; the helicopter sustained substantial damage.
Flight Details
The local passenger-repositioning flight departed from a landing zone located 22 miles east of Buffalo just prior to the accident. Visual meteorological conditions prevailed, and no flight plan had been filed. The purpose of the flight was to pick up a biologist conducting land surveys.
Pilot Report
In a written statement, the pilot reported arriving at the landing zone and circling to assess wind conditions. The landing zone was within a 3/4-mile diameter bowl-like depression. After landing to pick up the passenger, the pilot noted that he transitioned out of effective translational lift (ETL) earlier than expected, attributing this to a reduced headwind caused by the enclosed terrain. During acceleration to ETL speed after departure, the rotor speed began to decay. The pilot observed that his ground speed was faster than anticipated. He lowered the collective and added forward cyclic, but could not maintain enough rotor speed for sustained flight. He flew the helicopter approximately 1/4 mile further trying to locate a safe landing area. With airspeed and rotor speed decaying, the pilot elected to land on a 30-degree uphill slope. After landing, the helicopter rolled back, causing the tail rotor to contact the ground and resulting in substantial damage to the tail rotor drive system.
Post-Accident Observations
After the accident, the pilot walked up an embankment above the accident site to observe wind conditions. He noted that the winds had shifted 180 degrees from his initial pre-accident observation.
Environmental Conditions
The accident occurred at an altitude of approximately 4,300 feet mean sea level (msl). The closest official weather observation station was at Johnson County Airport, Buffalo, located about 24 miles west of the accident site, at an elevation of 4,968 feet msl. An aviation routine weather report issued at 1353 reported winds from 010 degrees at 13 knots, gusting to 19 knots; visibility 10 statute miles; clear skies; temperature 28 degrees Celsius; dew point 12 degrees Celsius; altimeter 30.01 inches of mercury.
Mechanical Status
The pilot stated that the helicopter and engine had no mechanical failures or malfunctions during the flight.