# NTSB CHI89FA071: Sikorsky S-58T, N4247U, Milwaukee, WI, April 11, 1989

- Type: NTSB accident investigation
- Classification: Accident · Serious injuries · Field investigation · Final report
- Date: April 11, 1989, 10:31 local (15:31 UTC)
- Place: Milwaukee, WI
- Coordinates: 42.980186, -87.900184 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=42.9802&lon=-87.9002&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: Serious injuries
- Injuries: 1 serious
- Status: Completed, report June 30, 1992
- Report: Approved by Office Director
- NTSB case key (mKey): 14250
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI89FA071
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/14250/pdf
- Page: https://openairdocs.org/ntsb/CHI89FA071

## Probable cause

DISCONNECT OF THE TAILROTOR DRIVE SHAFT COUPLING.

## Sequence of events

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

- Airframe/component/system failure/malfunction, hover
  - rotor drive system,tail rotor drive shaft coupling - disconnected (cause)
  - rotor drive system,tail rotor drive shaft - bent (contributing factor)
- Loss of control - in flight, hover
  - directional control - restricted, pilot in command (contributing factor)
- In flight collision with terrain/water, descent - emergency
  - terrain condition - dirt bank/rising embankment
  - directional control - restricted, pilot in command (contributing factor)

## Analysis

THE ACCIDENT HELICOPTER DESCENDED INTO SLOPING TERRAIN AND ROLLED OVER WHILE PERFORMING EXTERNAL LOAD OPERATIONS. THE HELICOPTER HAD JUST PICKED UP A LOAD AND WAS MOVING LATERALLY WHEN IT SUSTAINED A LOSS OF ANTI-TORQUE CONTROL AND THE FUSELAGE STARTED AN UNCOMMANDED AND UNCONTROLLED ROTATION TO THE RIGHT. THE PIC WAS ABLE TO JETTISON HIS EXTERNAL LOAD INTO A CLEAR AREA AND MOVE THE HELICOPTER AWAY FROM OBSTRUCTIONS BEFORE INITIATING AN OUT OF GROUND EFFECT HOVERING AUTOROTATION.

## Aircraft

- Registration: N4247U (not matched to a registry record)
- Reported make and model: SIKORSKY S-58T
- Category: Helicopter
- Serial number: 58-1537
- Airframe hours: 4326
- Engines: P&W PT6T-6 970 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Other work use, Part 133
- Registered owner: Midwest Truxton
- Airworthiness certificate: Standard, Transport
- Last inspection: Continuous airworthiness, March 15, 1989, 17 hours before
- Departed: MKE, MILWAUKEE, WI

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 44; commercial; instrument ratings: helicopter; medical: class 2, valid medical--no waivers/lim.; seat: right; flight hours: 9,562 total, 3,400 in this make and model, 8,275 as pilot in command, 99 in the last 90 days, 48 in the last 30 days, 3 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 210° at 10 knots, gusting 20
- Visibility: 7 statute miles
- Lowest ceiling: 25,000 ft overcast
- Temperature: 43 °F, dew point 18 °F
- Altimeter: 30.00 inHg
- Observed at: MKE, 3 nm away

## 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 19890411007609A](https://openairdocs.org/incident/19890411007609A), Apr 11, 1989: Skrsky S58BT, Milwaukee, WI, Substantial damage. Tail rotor driveshaft separated during long line hover. Dropped load and autorotated partial control and crashed.

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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