# NTSB SEA95LA022: Hiller UH-12C, N54594, Twisp, WA, November 28, 1994

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: November 28, 1994, 14:40 local (22:40 UTC)
- Place: Twisp, WA
- Coordinates: 48.319126, -119.930183 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=48.3191&lon=-119.9302&mi=10
- Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report June 29, 1995
- Report: Approved by Office Director
- NTSB case key (mKey): 42088
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA95LA022
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/42088/pdf
- Page: https://openairdocs.org/ntsb/SEA95LA022

## Probable cause

AN UNEXPLAINED LOSS OF POWER AND THE STUDENT PILOT'S DELAYED APPLICATION OF COLLECTIVE DURING THE LANDING FLARE.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Loss of engine power, landing - flare/touchdown
  - reason for occurrence undetermined
- Hard landing, landing - flare/touchdown
  - collective - delayed, pilot in command (cause)

## Analysis

WHEN THE STUDENT PILOT APPLIED POWER DURING THE LANDING FLARE OF A PRACTICE AUTO ROTATION THE ENGINE DID NOT RESPOND. HE THEN TRANSITIONED TO A FULL AUTOROTATION BUT WAS LATE APPLYING COLLECTIVE TO FLARE BEFORE TOUCHDOWN AND A MAIN ROTOR BLADE IMPACTED THE TAILBOOM. NO MECHANICAL MALFUNCTION OF THE HELICOPTER'S POWERPLANT WAS DISCOVERED.

## Factual narrative

On November 28, 1994, approximately 1440 hours Pacific standard time (PST), a Hiller UH-12C helicopter, N54594, registered to and being flown by Ross C. Darling, a student pilot, was substantially damaged during a hard landing following a loss of power at the Twisp Municipal Airport, Twisp, Washington.  The pilot was uninjured. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was an instructional solo flight, was to have been operated under 14CFR91, and originated from the Twisp airport approximately 15 minutes before the accident.

The student pilot reported that he was conducting a practice autorotation from approximately 1000 feet above ground commencing with a 300 RPM split between the engine/rotor tachometers. He reported applying carburetor heat and then reducing power to yield a 500-600 RPM split between the engine/rotor tachometers.

Approaching 150 feet above ground, he began applying power with no effect. He transitioned into a full autorotation and between 50-75 feet above ground began his flare. He stated that he "began to apply collective but was (a) second slow fully levelling (the) helicopter." During the touchdown the tail boom was severed when it was struck by one of the rotor blades.

FAA Inspector Doug Vaubel inspected the helicopter's Franklin engine subsequent to the accident and found no significant mechanical malfunctions.

## Aircraft

- Registration: [N54594](https://openairdocs.org/aircraft/N54594), registered now, S/N 873 (OpenAirDocs)
- Reported make and model: HILLER UH-12C
- Registry model: [Hiller UH-12C](https://openairdocs.org/model/hiller-uh-12c) (registry code 4360116) (OpenAirDocs)
- Registry engine: [Franklin 6VS-335 series](https://openairdocs.org/engine/franklin-6vs-335-series) (registry code 27040, reciprocating) (OpenAirDocs)
- Category: Helicopter
- Serial number: 873
- Airframe hours: 2939
- Engines: FRANKLIN 6V-335-B 210 horsepower reciprocating
- Damage: Substantial damage
- Flight: Instructional, Part 91
- Registered owner: Darling, Ross, C.
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, May 30, 1994, 8 hours before
- Departed: 2S0
- Airport: 2S0, Twisp Municipal, runway 10, 2,690 × 36 ft, asphalt

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 49; student; medical: class 3, valid medical--no waivers/lim.; seat: center; flight hours: 153 total, 147 in this make and model, 115 as pilot in command, 3 in the last 90 days

## Weather

- Conditions: Visual (VMC), Day
- Wind: calm
- Visibility: 20 statute miles
- Lowest ceiling: none
- Temperature: 21 °F

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19941128039569A](https://openairdocs.org/incident/19941128039569A), Nov 28, 1994: Hiller UH12C, Twisp, WA, Substantial damage. Failed to timely flare from practice autorotation. Impacted hard. Main rotors chopped tailboom.

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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