# NTSB LAX91LA079: Robinson R-22 HP, N21439, Scottsdale, AZ, January 25, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: January 25, 1991, 08:40 local (15:40 UTC)
- Place: Scottsdale, AZ
- Coordinates: 33.610881, -111.890846 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=33.6109&lon=-111.8908&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report March 31, 1993
- Report: Approved by Office Director
- Safety recommendations: Yes
- NTSB case key (mKey): 27098
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX91LA079
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27098/pdf
- Page: https://openairdocs.org/ntsb/LAX91LA079

## Probable cause

THE FAILURE OF THE DRIVE BELTS DUE TO EXCESSIVE WEAR OF THE CLUTCH ASSEMBLY UPPER SHEAVE AND THE PILOT'S INACCURATE FLARE DURING THE TERMINATION OF THE AUTOROTATION.  A FACTOR IN THE ACCIDENT WAS THE INADEQUATE DESIGN OF THE CLUTCH ASSEMBLY UPPER SHEAVE.

## 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,main rotor drive belt - failure,total (cause)
  - acft/equip,inadequate design, manufacturer (contributing factor)
  - rotor drive system,main rotor driving pulley - worn (cause)
- Forced landing, descent - emergency
  - autorotation - performed, pilot in command
- On ground/water encounter with terrain/water, landing - flare/touchdown
  - flare - inaccurate, pilot in command (cause)
- Roll over, landing - flare/touchdown

## Analysis

THE PILOT, AFTER SEEING THE HELICOPTER'S CLUTCH CAUTION LIGHT ILLUMINATE, HEARD A LOUD 'BANG'. HE LOWERED THE COLLECTIVE AND ENTERED AN AUTOROTATIVE DESCENT. HE TERMINATED LOW TO THE TERRAIN, AND THE AIRCRAFT STRUCK TAIL STINGER FIRST, CAUSING IT TO BOUNCE AND THEN ROLL OVER. A VISUAL INSPECTION OF THE HELICOPTER REVEALED TWO OF THE DRIVE BELTS HAD FAILED, CAUSING A DRIVE TRAIN SEPARATION. THE HELICOPTER MANUFACTURER DISCOVERED THE BELTS FAILED AS A RESULT OF EXCESSIVE WEAR ON THE CLUTCH ASSEMBLY UPPER SHEAVE. THE EXCESSIVE WEAR ON THE SHEAVE WAS CAUSED BY THE BELTS, GRITS, AND SAND. THIS CREATED A SHARP EDGE ON THE SHEAVE WHICH CAUSED THE FAILURE OF THE BELTS.

## Aircraft

- Registration: [N21439](https://openairdocs.org/deregistered/N21439-1994-02-04), registration cancelled 1994-02-04, S/N 0096 (OpenAirDocs)
- Reported make and model: ROBINSON R-22 HP
- Registry model: [Robinson Helicopter R22](https://openairdocs.org/model/robinson-helicopter-r22) (registry code 7640102) (OpenAirDocs)
- Category: Helicopter
- Serial number: 0096
- Engines: LYCOMING O-320-B2C 160 horsepower reciprocating
- Damage: Substantial damage
- Flight: Instructional, Part 91
- Operator: Arizona Wing & Rotor, Inc.

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 25; student; medical: class 2, valid medical--no waivers/lim.; flight hours: 58 total, 58 in this make and model, 58 in the last 90 days, 48 in the last 30 days, 2 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: calm
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 55 °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 19910125001109A](https://openairdocs.org/incident/19910125001109A), Jan 25, 1991: Robsin R22, Scottsdale, AZ, Substantial damage. Rotor drive belts came off pulley. Autorotated but entered dynamic rollover on landing. Belts worn from gritty sand

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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