# NTSB LAX91LA320: Sikorsky SK-58, N58WH, Daggett, CA, July 22, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: July 21, 1991, 21:40 local (Jul 22, 1991, 04:40 UTC)
- Place: Daggett, CA
- Coordinates: 34.859153, -116.810943 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=34.8592&lon=-116.8109&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 3 uninjured
- Status: Completed, report April 8, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 27298
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX91LA320
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27298/pdf
- Page: https://openairdocs.org/ntsb/LAX91LA320

## Probable cause

THE FAILURE OF AN ENGINE CONNECTING ROD CAUSING A REDUCTION OF ENGINE POWER TO THE POINT WHERE LEVEL FLIGHT COULD NOT BE MAINTAINED.  A FACTOR IN THE ACCIDENT WAS THE DARK NIGHT CONDITIONS WHICH RESTRICTED THE PILOT'S ABILITY TO SELECT THE BEST LANDING SITE.

## Sequence of events

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

- Loss of engine power(partial) - mech failure/malf, cruise - normal
  - engine assembly,connecting rod - failure,total (cause)
- Forced landing, descent - emergency
  - light condition - dark night (contributing factor)
  - visual/aural detection, pilot in command
  - terrain condition - rough/uneven (contributing factor)
- On ground/water encounter with terrain/water, landing - roll
  - terrain condition - berm
- Roll over, landing - roll

## Analysis

WHILE RETURNING FROM AN EXTERNAL LOAD OPERATION, THE HELICOPTER'S ENGINE STARTED VIBRATING AND THEN STARTED BACK FIRING.  THE PILOT REPORTED HEARING A LOUD 'BANG' AND THEN NOTED A DECREASE IN ENGINE POWER.  HE PERFORMED NECESSARY EMERGENCY PROCEDURES AND ENTERED AN AUTOROTATION.  HE SAID THAT HE TOUCHED DOWN WITH SOME FORWARD SPEED.  THE HELICOPTER HIT A DIRT BERM.  THE ROTOR BLADES CONTACTED THE GROUND AND THE AIRCRAFT ROLLED OVER.  AN ENGINE TEARDOWN WAS PERFORMED UNDER THE SUPERVISION OF AN FAA AIRWORTHINESS INSPECTOR.  A BROKEN ROD WAS FOUND DURING THE TEARDOWN. THE TEARDOWN WAS TERMINATED AT THAT POINT AND THE REASON FOR THE BROKEN ROD WAS NOT DETERMINED.

## Aircraft

- Registration: N58WH (not matched to a registry record)
- Reported make and model: SIKORSKY SK-58
- Category: Helicopter
- Serial number: 11
- Engines: WRIGHT R-1820 1200 horsepower reciprocating
- Damage: Substantial damage
- Flight: Other work use, Part 133
- Operator: Associated Helicopter Services
- Last inspection: Unknown, January 2, 2000
- Departed: DAG, BARSTOW, CA

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 42; flight instructor, commercial; medical: class 1, valid medical--w/ waivers/lim; flight hours: 6,000 total, 1,778 in this make and model, 49 in the last 90 days, 10 in the last 30 days

## Weather

- Conditions: Visual (VMC), Night/dark
- Wind: 270° at 9 knots
- Visibility: 30 statute miles
- Lowest ceiling: none

## 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 19910722029099A](https://openairdocs.org/incident/19910722029099A), Jul 22, 1991: Skrsky S58H, Daggett, CA, Substantial damage. Lost partial power,engine backfiring. Autorotated to land. Hit berm. Rolled over. Found broken connecting rod.

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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