N3755ZBell 47G-2 · 1955

On January 11, 2019, about 1440 mountain standard time, a Bell 47G-2 helicopter, N3755Z, collided with terrain while maneuvering near Belen, New Mexico. The pilot and passenger were not injured, and the helicopter was substantially damaged. The helicopter was owned by the pilot and operated under Title 14 Code of Federal Regulations (CFR) Part 91 as a personal flight without a flight plan. Day visual meteorological conditions prevailed for the local flight that departed Belen Regional Airport (BRG), near Belen, New Mexico, about 1400.The pilot stated that shortly before the accident he had maneuvered the helicopter into an out-of-ground effect hover about 50 ft above the ground. The pilot reported that the carburetor heat was not engaged while he flew the helicopter in the hover. The pilot stated that he "got complacent about maintaining main rotor speed" and subsequently observed an unsafe main rotor speed. The pilot lowered the collective control for an immediate landing and engaged the carburetor heat. He attempted to reduce the helicopter's descent rate before impact by increasing the collective control, but the helicopter landed hard in the soft terrain. The main rotor blades subsequently impacted the tail boom and tail rotor. The pilot reported that after impact the engine continued to run at about 1,500 rpm, and that he secured the engine by turning the fuel valve to OFF. The pilot reported no preimpact mechanical anomalies with the helicopter that would have precluded normal operation. The pilot postulated that an insufficient main rotor speed had precluded him from making a normal flare and landing. The pilot stated that the engine might have encountered carburetor icing as he maneuvered the helicopter into the out-of-ground effect hover at a decreased engine power setting, which, in turn, might have contributed to his failure to maintain adequate main rotor speed while hovering.

A postaccident review of available meteorological data established that day visual meteorological conditions prevailed at the accident site. The nearest aviation weather reporting station was located at Belen Regional Airport (BRG), about 3 miles north of the accident site. At 1435, about 5 minutes before the accident, the BRG automated surface observing system reported: wind 310° at 8 knots, 10 miles surface visibility, clear sky, temperature 8°C, dew point 1°C, and an altimeter setting 29.96 inches of mercury.

According to a carburetor icing probability chart contained in FAA Special Airworthiness Information Bulletin CE-09-35, entitled "Carburetor Icing Prevention", the recorded temperature and dew point were in the range of susceptibility for the formation of carburetor icing at all engine power settings.

On December 1, 2012, about 1420 central standard time, a Bell 47G-2 helicopter, N3755Z, collided with trees and impacted terrain near Walkerville, Michigan. The commercial pilot was fatally injured and the passenger was seriously injured. The helicopter was substantially damaged. The helicopter was owned and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which operated without a flight plan. The flight originated from private property at an undetermined time.According to information provided by local law enforcement and the responding Federal Aviation Administration inspectors, the helicopter travelled at a low altitude when a loud noise was heard by the passenger. The helicopter descended and impacted trees and a marsh.

The pilot, age 49, held a commercial helicopter pilot certificate. On May 2, 2000, the pilot was issued an unrestricted second class medical certificate. On the medical application, the pilot reported having accumulated 4,000 hours of total time. The pilot's logbook was not available for review during the investigation. It is unknown when the pilot accomplished his most recent flight review.

The single engine, low skid, full bubble canopy, three-seat helicopter, serial number 1698, was manufactured in 1957. It was powered by a 200-horsepower Lycoming VO-435-A1 engine. The log books were not available for review and the helicopter's last annual inspection is unknown.

At 1414, an automated weather reporting facility at Fremont Municipal Airport, located 17 nautical miles to the south-southeast of the accident location, reported wind from 110 degrees at 7 knots, visibility 4 miles, haze, ceiling broken at 1,000 feet, broken at 1,600 feet, temperature 43 degrees Fahrenheit (F), dew point 37 F, and a barometric pressure of 30.03 inches of mercury.

The wreckage was located in a wooded marsh in the Manistee National Forest, also known as Tanner's Swamp. Only the trees within about a rotor disk circumference of the helicopter exhibited blade strikes. The helicopter came to rest on its left side. All parts of the helicopter were accounted for at the accident site and the helicopter was recovered and transported to a hanger for an examination.

Inspectors from the Federal Aviation Administration and representatives from Scott's Bell 47 attended the examination. The main rotors were fractured a few feet from the rotor mast with corresponding impact damage to the leading edge of the blades. The flight controls were fractured in several locations, but exhibited no preimpact malfunctions. Several of the engine cooling fan blades had leading edge damage with signatures consistent with the fan being driven at the time of impact. Engine control continuity was established from the controls to the carburetor throttle shaft. The main fuel strainer and carburetor fuel inlet finger screen contained an unmeasured amount of fuel.

An autopsy was conducted on the pilot by Spectrum Health, Grand Rapids, Michigan. The cause of death was blunt force injuries of the chest and abdomen. The manner of death was ruled an accident.

Forensic toxicology was performed on specimens from the pilot by the FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma. The specimens tested negative for carbon monoxide, ethanol, and drugs.

Bell 47 Flight Characteristics

Scott's Bell 47 representatives reported the following concerning turns in a Bell 47:

A characteristic of the Bell 47 is a best power to airspeed combination encountered in level flight at 45 miles per hour (MPH), indicated airspeed (IAS.) This characteristic is often demonstrated in flight training and may be validated when in level flight at 45 MPH IAS increasing or decreasing airspeed by cyclic input alone results in loss of altitude. For this reason pilots must always be mindful of airspeed and power when maneuvering at low level and reduced airspeed. As 45 MPH is the best power / airspeed combination and also the target airspeed for best autorotational descent, this is also the best and safest airspeed selected for low level observation and reconnaissance flight. When turning downwind from stabilized flight into wind at 45 MPH IAS, if no control input is made, the turn into downwind will result in reduced airspeed and the aircraft will tend to settle. The settling tendency is avoided by a coordinated management of increased power and airspeed control to maintain the desired altitude.