GARLICK UH1H near Walla Walla, WA — 2015-07-21

Probable cause

The helicopter’s reduction in aerodynamic lift while operating in variable wind conditions for reasons that could not be determined because postaccident examination did not reveal any evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation.

NTSB narrative

The commercial pilot reported that the helicopter was in a 165-ft hover in a narrow creek valley, over a shallow creek and that he was filling a fire bucket, which was attached to the helicopter via a long line. The terrain rose between 200 and 400 ft on either side of the creek. About 1 minute into the hover, the pilot felt the helicopter start to settle. He applied collective to arrest the settling, but the helicopter continued to settle. The pilot said that there was no yaw or unusual vibration or noise during the event, only a smooth settling of the helicopter and that the engine did not respond when he manipulated the collective. He immediately lowered the collective and performed a hovering autorotation toward an embankment. When the pilot raised the collective for the landing, the engine did not respond. The rotors struck several trees, then the helicopter spun 180°, landed hard, and rolled over onto its right side. After the accident, the engine continued to run until the pilot shut off the fuel and secured the battery. The helicopter was destroyed by postcrash fire. Postaccident examination of the helicopter did not reveal any evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation. Examination of the engine revealed compressor blade damage, rotational scoring witness marks, and metal splatter, consistent with the engine operating at the time of the accident. An automated surface observation system (ASOS) located 10 miles west of the accident reported that, about 1 hour before the accident, the wind was from 250°, gusting to 22 knots. An unofficial weather station located 6 miles southwest of the accident site recorded that, about 3 minutes before the accident, the wind was from 239o at 20 knots, gusting to 30 knots. The ASOS reported that, about 13 minutes after the accident, the wind was from 239o at 14 knots. Given these conditions, orographic wind turbulence could not be ruled out as a factor.

Analysis

Primary failure mode

Engine power loss

First missed decision gate

Pilot could have aborted the hover when sensing settling instead of continuing.

NTSB coding

• Loss of lift · Maneuvering-hover

Evidence available

• Photos
• 9 docket documents

Docket documents9

• Evidence Control Formform
• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Release of Aircraft Wreckage, NTSB Form 6120.15form
• Memorandum for Record - Telephone Interview, Pilotinterview
• Statement of Party Representatives to NTSB Investigationinterview
• Airframe and Engine Examinationother
• Maps or Charts of Accident Areaother
• On-Scene Photos (Courtesy of AvTech)photos
• Weather Reports and Recordsreport

Related mishaps

• MICHAEL R ALEXANDER MOSQUITO XE

  2018-05-02 · Iron Station, NC

• ROBINSON HELICOPTER R22 BETA

  2009-02-25 · O'Donnell, TX