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N181W accident description

Arkansas map... Arkansas list
Crash location 34.230556°N, 94.059722°W
Nearest city Umpire, AR
34.278998°N, 94.050753°W
3.4 miles away
Tail number N181W
Accident date 24 Aug 2004
Aircraft type Bell 212
Additional details: None

NTSB Factual Report

On August 24, 2004, about 1430 central daylight time, a Bell BH212 twin-engine helicopter, N181W, was substantially damaged during loss of control shortly after departure, approximately five miles south of Umpire, Arkansas. The commercial pilot, the sole occupant, sustained minor injuries. The helicopter was registered to and operated by Weyerhaeuser Company of SeaTac, Washington. Visual meteorological conditions prevailed, and a flight plan was not filed for the local 14 Code of Federal Regulations Part 137 agricultural flight.

In a written statement, the 3,807-hour pilot reported that while spraying, his "Satloc" spray navigation system computer "crashed." He returned to the heliport, landed, and after rebooting the "Satloc" system, was able to recover his spray data. While at the heliport, the helicopter was fueled for a total of 600 pounds, and chemical mix was added for a total of 392 gallons. The helicopter departed approximately 70 pounds under it's certified gross weight, which was 11,200 pounds. The pilot reported, "the take-off was normal with speed building normally and the helicopter climbing slowly." He then increased the climb rate with "slight" rearward cyclic movement. The helicopter responded by initially climbing then "immediately" it began to descend. During the descent, the pilot attempted to dump the chemical load, but reported that the dump doors failed to operate until his fourth try. Shortly thereafter, the main rotor blades struck trees and the helicopter descended to the ground and came to rest in an upright position.

A Federal Aviation Administration (FAA) aviation safety inspector performed an on-scene examination of the helicopter. He reported that the helicopter came to rest in heavily wooded terrain and sustained structural damage. The four chemical dump valves were examined by the FAA inspector and the operator's lead mechanic. The examination revealed no mechanical deficiencies with the valves.

Interpolation of the published Hover Ceiling In-Ground Effect performance chart revealed that the helicopter was within the performance envelope.

At 1453 central daylight time, the weather observation facility at Helms Sevier County Airport (DEQ), De Queens, Arkansas, which is located approximately 20 miles southwest of the accident site, reported wind variable at six knots, visibility 10 statute miles, few clouds at 4,600 feet, temperature 91 degrees Fahrenheit, dew point 73 degrees Fahrenheit, and a barometric pressure setting of 29.86 inches of Mercury. The investigator-in-charge (IIC) calculated the density altitude at 3,155 feet.

According to the Federal Aviation Administration (FAA) Rotorcraft Flying Handbook, pages 11-5 to 11-7, Vortex Ring State (Settling with Power), "Vortex ring state describes an areodynamic condition where a helicopter may be in a vertical descent with up to maximum power applied, and little, or no cyclic authority. The term 'settling with power' comes from the fact that the helicopter keeps settling even though full engine power is applied. In a normal out-of-ground effect-hover, the helicopter is able to remain stationary by propelling a large mass of air down through the main rotor. Some of the air is recirculated near the tips of the blades, curling up from the bottom of the rotor system and rejoining the air entering the rotor from the top. However, when the helicopter begins to descend vertically, it settles into its own downwash, which greatly enlarges the tip vortices. In this vortex ring state, most of the power developed by the engine is wasted in accelerating the air in a doughnut pattern around the rotor. In addition, the helicopter may descend at a rate that exceeds the normal downward induced-flow rate of the inner blade sections. As a result, the airflow of the inner blade sections is upward relative to the disc. This produces a secondary vortex ring in addition to the normal tip-vortices. The secondary vortex ring is generated about the point on the blade where the airfoil changes from up to down. The result is an unsteady turbulent flow over a large area of the disc. Rotor efficiency is lost even though power is still being supplied from the engine."

NTSB Probable Cause

The pilot's encounter with settling with power resulting in a loss of control. A contributing factor was the high density altitude.

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