# NTSB LAX91LA369: Hiller UH12D, N100HH, Sparks, NV, August 25, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: August 24, 1991, 19:50 local (Aug 25, 1991, 02:50 UTC)
- Place: Sparks, NV
- Coordinates: 39.599884, -119.690567 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=39.5999&lon=-119.6906&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report April 8, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 27337
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX91LA369
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27337/pdf
- Page: https://openairdocs.org/ntsb/LAX91LA369

## Probable cause

THE ENCOUNTER WITH ROUGH, UNSUITABLE TERRAIN DURING A PRECAUTIONARY LANDING. CONTRIBUTING TO THE ACCIDENT WAS THE PILOT'S DECISION TO MAKE AN AUTOROTATION AFTER ENCOUNTERING AN AIRFRAME VIBRATION.

## Sequence of events

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

- Airframe/component/system failure/malfunction, cruise - normal
  - rotor drive system,tail rotor drive shaft bearing - vibration (cause)
- Hard landing, landing - flare/touchdown
  - terrain condition - rough/uneven (cause)
  - misc rotorcraft,tail boom - sheared

## Analysis

THE CERTIFICATED PRIVATE HELICOPTER PILOT, THE SOLE OCCUPANT, WAS ON A LOCAL AREA FLIGHT WHEN A STRONG, MEDIUM TO HIGH FREQUENCY VIBRATION DEVELOPED IN THE TAIL SECTION OF HIS HELICOPTER.  THE PILOT ELECTED TO MAKE A PRECAUTIONARY LANDING IN AN OPEN DIRT AREA, AND EXECUTED AN AUTOROTATION.  AFTER TOUCHDOWN THE HELICOPTER SLID ON ROUGH, ROCKY TERRAIN, CAUSING THE MAIN ROTOR BLADES TO CONTACT THE TAIL BOOM.  THREE FEET OF THE TAIL BOOM INCLUDING THE TAIL ROTOR GEAR BOX AND BLADES, AND THE TAIL ROTOR DRIVE SHAFT WERE SEVERED.  AN EXAMINATION OF THE TAIL ROTOR DRIVE SHAFT AT THE POSITION WHERE A SUPPORT BEARING IS MOUNTED, REVEALED SIGNS OF HEAT AND WEAR.  DURING THE IMPACT SEQUENCE, THE DRIVE SHAFT SUPPORT BEARING DEPARTED THE HELICOPTER AND WAS NOT RECOVERED.

## Aircraft

- Registration: [N100HH](https://openairdocs.org/deregistered/N100HH-2018-05-30), registration cancelled 2018-05-30, S/N 1266, built 1961 (OpenAirDocs)
- Reported make and model: HILLER UH12D
- Registry model: [Hiller UH-12D](https://openairdocs.org/model/hiller-uh-12d) (registry code 4360118) (OpenAirDocs)
- Registry engine: [Lycoming VO-435 series](https://openairdocs.org/engine/lycoming-vo-435-series) (registry code 41525, reciprocating) (OpenAirDocs)
- Category: Helicopter
- Serial number: 1266
- Airframe hours: 5868
- Engines: LYCOMING VO-435-AIC 250 horsepower reciprocating
- Damage: Substantial damage
- Flight: Personal, Part 91
- Operator: Pathfinder Technology Inc., doing business as Richard Swartzendruber
- Registered owner: Pathfinder Technology Inc.
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, March 12, 1991, 10 hours before
- Departed: NONE, RENO, NV
- Destination: 45D, STEAD, NV

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 50; private; medical: class 2, valid medical--no waivers/lim.; seat: center; flight hours: 265 total, 265 as pilot in command, 5 in the last 90 days, 2 in the last 30 days, 1 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Dusk
- Wind: 270° at 5 knots
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 81 °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 19910824036649A](https://openairdocs.org/incident/19910824036649A), Aug 24, 1991: Hiller UH12D, Sparks, NV, Substantial damage. Detected vibration. Autorotated to rough shale rock. Chopped tailboom. Bearing on tail rotor shaft heat damage.

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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