# NTSB CHI84FA226: Hiller UH-12E, N93431, Merrimac, WI, June 10, 1984

- Type: NTSB accident investigation
- Classification: Accident · Fatal · Field investigation · Final report
- Date: June 10, 1984, 13:36 local (18:36 UTC)
- Place: Merrimac, WI
- Coordinates: 43.370269, -89.619346 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=43.3703&lon=-89.6193&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Highest injury: Fatal
- Injuries: 1 fatal
- Status: Completed
- Report: Approved by Office Director
- NTSB case key (mKey): 12402
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI84FA226
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/12402/pdf
- Page: https://openairdocs.org/ntsb/CHI84FA226

## Sequence of events

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

- Airframe/component/system failure/malfunction, approach - vfr pattern - final approach
  - electrical system,voltmeter - improper (cause)
  - maintenance,replacement - improper, other maintenance personnel (cause)
  - emergency procedure - not selected, pilot in command (cause)
  - electrical system,battery - exploded (cause)
- In flight collision with terrain/water, descent - uncontrolled
  - fluid,fuel - fire (cause)

## Analysis

THE ACFT CRASHED AND BURNED AFTER AN IN-FLT EXPLOSION AT ABOUT 75 FT AGL AS THE ACFT APPROACHED TO LAND. THE ACFT HAD EXPERIENCED ELECTRICAL PROBLEMS OF OVERHEATING GENERATORS AND IRREGULAR VOLTAGE OUTPUTS ON 2 PREVIOUS OCCASIONS. THE PLTWAS TOLD AFTER SOME REPAIRS THAT IF HE SMELLED ANYTHING HOT TO PULL THE GENERATOR CIRCUIT BREAKER. POST-ACCIDENT ACFT EXAMINATION SHOWED A CONDITION OF THE VOLTAGE REGULATOR WHICH WOULD HAVE CAUSED CONTINUOUS CHARGING OF THE BATTERY. THE GENERATOR SHOWED SIGNS OF OVERHEATING AND THE BATTERY HAD EXPLODED AWAY FROM THE WRECKAGE WITH THE TERMINAL POLES MELTEDOFF.

## Aircraft

- Registration: N93431 (not matched to a registry record)
- Reported make and model: HILLER UH-12E
- Category: Helicopter
- Serial number: 1768
- Airframe hours: 1837
- Engines: LYCOMING VO-4540-C2A 305 horsepower reciprocating
- Damage: Destroyed
- Fire: Both
- Flight: Public aircraft, Part 91
- Registered owner: Sauk County Emergency Govt.
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, December 19, 1983, 4 hours before
- Departed: BARABOO, WI
- Flight plan: VFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 38; commercial, private; airplane ratings: single-engine land; medical: class 2, valid medical--no waivers/lim.; seat: left; toxicology performed; flight hours: 781 total, 567 in this make and model, 687 as pilot in command, 50 in the last 90 days, 25 in the last 30 days, 10 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 230° at 23 knots, gusting 33
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 75 °F, dew point 57 °F
- Altimeter: 29.00 inHg
- Observed at: MSN, 30 nm away

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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