CEN13LA086

The passenger reported that the pilot was maneuvering the helicopter over an area of tree-covered marsh at a low altitude when the helicopter entered a descent, collided with trees, and impacted the ground on its left side. An examination of the wreckage found damage consistent with the main rotor blades being driven by the engine when they contacted the trees. Although the passenger reported hearing a loud sound before the helicopter started descending, postaccident examination of the helicopter revealed no evidence of preimpact mechanical malfunction or failure that would have precluded normal operation. The circumstances of the accident are consistent with the pilot failing to maintain altitude while maneuvering at low airspeed and low altitude, which resulted in the helicopter descending into trees.

HISTORY OF FLIGHT 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. PERSONNEL INFORMATION 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. AIRCRAFT INFORMATION 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. METEOROLOGICAL INFORMATION 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. WRECKAGE AND IMPACT INFORMATION 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 thecarburetor throttle shaft. The main fuel strainer and carburetor fuel inlet finger screen contained an unmeasured amount of fuel. MEDICAL AND PATHOLOGICAL INFORMATION 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. ADDITIONAL INFORMATION 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.