# NTSB DEN91LA095: Bell 412, N20703, Grand Junction, CO, July 1, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: July 1, 1991, 15:00 local (21:00 UTC)
- Place: Grand Junction, CO
- Coordinates: 39.08078, -108.549804 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=39.0808&lon=-108.5498&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 3 uninjured
- Status: Completed, report February 8, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 18109
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN91LA095
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18109/pdf
- Page: https://openairdocs.org/ntsb/DEN91LA095

## Probable cause

THE PILOT'S FAILURE TO MAINTAIN ADEQUATE MAIN ROTOR RPM PRIOR TO TOUCHDOWN.  FACTORS WERE:  THE DISCONNECTED ENGINE TO TRANSMISSION DRIVE SHAFT AND THE INADEQUATE INSPECTION BY COMPANY MAINTENANCE PERSONNEL.

## Sequence of events

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

- Airframe/component/system failure/malfunction, cruise
  - rotor drive system,engine to transmission drive - disconnected (contributing factor)
  - maintenance,inspection - inadequate, company maintenance personnel (contributing factor)
- Forced landing, descent - emergency
  - autorotation - performed, pilot in command
- Hard landing, landing - flare/touchdown
  - rotor rpm - not maintained, pilot in command (cause)

## Analysis

DURING CRUISE FLIGHT, THE ENGINE TO TRANSMISSION DRIVE SHAFT FORWARD COUPLING OVERHEATED AND FAILED. THE PILOT EXECUTE AN AUTORATATION. DURING THE LANDING FLARE, THE PILOT DID NOT MAINTAIN ADEQUATE ROTOR RPM AND THE HELICOPTER LANDED HARD RESULTING IN SKID COLLAPSE. COMPANY MAINTENANCE PERSONNEL DISPATCHED THE HELICOPTER WITH A KNOWN DRIVE SHAFT COUPLING GREASE LEAK WHICH THEY HAD ATTEMPTED TO STOP BY USING AN UNAPPROVED SILICON SEALANT. THEY HAD REPACKED THE 500 PLUS HOUR COUPLING TWO TIMES PRIOR TO THE ACCIDENT. THE NORMAL REPACK INTERVAL WAS ONCE EVERY 600 HOURS. EXAMINATION OF THE FAILED DRIVE SHAFT DID NOT REVEAL ANY MISALIGNMENT, BUT DID ISOLATE HEAT RELATED FAILURE AREAS OF THE FORWARD COUPLING END.

## Aircraft

- Registration: N20703 (not matched to a registry record)
- Reported make and model: BELL 412
- Category: Helicopter
- Serial number: 33017
- Engines: P&W PT6T-3B 1350 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Positioning, Part 91
- Operator: Air Methods Corporation
- Registered owner: Air Methods Corporation
- Departed: GJT, GRAND JUNCTION, CO
- Destination: U43, MONTICELLO, UT

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 42; airline transport; airplane ratings: multi-engine land; instrument ratings: helicopter; medical: class 1, valid medical--no waivers/lim.; flight hours: 4,010 total, 300 in this make and model, 2,500 as pilot in command, 40 in the last 90 days, 12 in the last 30 days, 2 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 180° at 7 knots
- Visibility: 70 statute miles
- Lowest ceiling: none
- Temperature: -0 °F, dew point -0 °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 19910701025659A](https://openairdocs.org/incident/19910701025659A), Jul 1, 1991: Bell 412, Grand Junction, CO, Substantial damage. Tranmission main drive shaft disengaged and overheated. Collapsed skids on run on autorotation in soft ground.

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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