History of Flight
On July 20, 2015, about 1740 Pacific daylight time, a Garlick Helicopters UH-1H (N121PT) experienced a hard landing after the pilot sensed the helicopter settling while in a high hover. The accident occurred 10 miles east of Walla Walla, Washington. The commercial pilot received minor injuries, and the helicopter was destroyed by a postaccident fire. The helicopter was registered to LRH Equipment LLC and operated under 14 CFR Part 133 on contract to the Oregon State Department of Forestry for firefighting services. Visual meteorological conditions prevailed, and the flight operated on a company visual flight rules flight plan.
The pilot reported that he was hovering at 165 feet over a shallow creek, filling a fire bucket attached via a long line. The creek bed was in a narrow valley with terrain rising 200 to 400 feet on either side. Approximately one minute into the hover, the pilot sensed the helicopter start to settle. He applied collective to arrest the descent, but the helicopter continued to settle. The pilot noted no yaw, unusual vibration, or noise, only a smooth settling, and the engine system did not respond to collective input. He immediately lowered the collective and performed a hovering autorotation toward the stream embankment. When he applied up collective for landing, the engine did not respond. The main rotor struck trees, the helicopter turned 180 degrees, landed hard, and rolled onto its right side. The engine continued running until the pilot shut off the fuel and secured the battery after the accident. The pilot egressed and hiked out of the area.
Weather Information
Weather conditions at Walla Walla Regional Airport, 10 miles west of the accident site, were reported by the ASOS at 1753 PDT as wind from 250 degrees at 14 knots, visibility 10 statute miles, clear sky, temperature 36°C, dew point -2°C, and pressure 29.83 inHg. About one hour prior, the ASOS recorded wind from 250 degrees at 13 knots gusting to 22 knots. An unofficial weather station 6 miles southwest recorded wind from 239 degrees at 20 knots with gusts of 30 knots at 1743. The pilot stated that winds in the canyon were light and variable, while above the canyon, wind drove smoke from the fire to the north.
Wreckage and Impact Information
The helicopter wreckage was recovered and transported to Auburn, Washington. On October 1, 2015, the wreckage was examined by the NTSB investigator-in-charge (IIC), the pilot, an FAA inspector, and a Honeywell technical representative. The postcrash fire destroyed the fuselage, engine case, and main transmission case. All major components were laid out, including the engine, transmission, main rotor hub and blades, tail boom, and tail rotor hub and blades. The remaining wreckage was sorted from large grain bags. The majority of the helicopter was accounted for, but the fuel control, droop compensator, and half of the KaFlex shaft were missing, presumed destroyed or left at the accident site. No evidence of mechanical malfunctions or failures of the flight control system, main transmission, or rotor systems was found that would have precluded normal operation. Engine components were sent to Honeywell in Phoenix, Arizona, for further examination.
On December 9, 2015, a tear-down inspection was conducted at Honeywell under NTSB oversight. Honeywell determined that gas producer section blade failures resulted from short-term overheating beyond blade material capacity, combined with high rotational speeds causing stress rupture. Metallic splatter adhered to the combustion chamber deflector. The compressor section showed all axial compressor rotor blades separated or missing, and vane assemblies were fractured and bent. Brown earthen debris adhered to flow path surfaces and vanes of the centrifugal compressor impeller. Several vanes were bent opposite the rotation direction at the impeller inlet, and all vanes had leading edge damage. The shroud line edge showed rotational scoring with corresponding scoring on the impeller shroud. Honeywell concluded the damage was indicative of an engine rotating and operating at impact, with no pre-existing condition found that would have prevented normal operation.
Additional Information
The accident report referenced AC-00-57, Hazardous Mountainous Winds and Their Visual Indicators. An excerpt from Section 3.3 noted that aircraft engaged in low-level flight over mountainous terrain in strong winds (20 knots or greater at ridge level) can expect moderate or greater turbulence, strong updrafts and downdrafts, and strong rotor and shear zones, particularly for general aviation aircraft.