# NTSB DEN92IA074: Embraer EMB-120 RT, N221YV, Denver, CO, July 21, 1992

- Type: NTSB incident investigation
- Classification: Incident · No injuries · Incident investigation · Final report
- Date: July 21, 1992, 17:45 local (23:45 UTC)
- Place: Denver, CO
- Coordinates: 39.760925, -104.920112 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=39.7609&lon=-104.9201&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 26 uninjured
- Status: Completed, report May 26, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 18173
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN92IA074
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18173/pdf
- Page: https://openairdocs.org/ntsb/DEN92IA074

## Probable cause

OPEN AIR GROUND CIRCUIT BREAKERS THAT ALLOWED THE PROPELLERS TO OVERSPEED. A FACTOR WAS:  CLEAR AIR TURBULENCE.

## 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 - base leg/base to final
  - weather condition - turbulence,clear air (contributing factor)
  - electrical system,circuit breaker - open (cause)
  - throttle/power control - inadvertent, pilot in command
  - propeller system/accessories,blade - overspeed

## Analysis

THE CAPTAIN WAS FLYING THE AIRPLANE WITH HIS RIGHT HAND RESTING ON THE POWER CONTROLS.  AS THE AIRPLANE TURNED ONTO FINAL APPROACH, IT ENCOUNTERED TURBULENCE OF SUFFICIENT INTENSITY THAT THE CAPTAIN'S FEET CAME OFF THE RUDDER PEDALS. HE FELT A 'CLICK' IN HIS HAND AND 'THERE WAS AN INSTANTANEOUS PROPELLER OVERSPEED.'  THE ENGINE WAS EVENTUALLY SECURED BY CLOSING THE FUEL SHUTOFF VALVE AND AN UNEVENTFUL NO FLAP LANDING WAS MADE.  POST INCIDENT EXAMINATION DISCLOSED BOTH AIR GROUND CIRCUIT BREAKERS WERE OPEN.  THE LEFT ENGINE WAS FOUND TO BE FUNCTIONALLY DESTROYED.  A READOUT OF THE DIGITAL FLIGHT DATA RECORDER DISCLOSED THE MAXIMUM LEFT AND RIGHT PROPELLER RPM VALUES ATTAINED WERE 150.49% AND 120.4%, RESPECTIVELY.  VERTICAL ACCELERATION VALUES RANGED FROM .647 TO 1.26 G'S, AND LONGITUDINAL ACCELERATION VALUES RANGED FROM .037 TO .096 G'S.  THE RIGHT ENGINE TORQUE PEAKED AT 37%, WHILE THE LEFT ENGINE TORQUE REMAINED AT 0%. RIGHT ENGINE FUEL FLOW WAS 16% TO 19% LOWER THAN LEFT ENGINE FUEL FLOW, AND PROPELLER IMBALANCE VALUES FOR THE LEFT ENGINE WAS APPROXIMATELY 50% HIGHER THAN THOSE RECORDED FOR THE RIGHT ENGINE.

## Aircraft

- Registration: [N221YV](https://openairdocs.org/deregistered/N221YV-2013-08-15), registration cancelled 2013-08-15, S/N 120.221, built 1990 (OpenAirDocs)
- Reported make and model: EMBRAER EMB-120 RT
- Registry model: [Embraer EMB-120RT](https://openairdocs.org/model/embraer-emb-120rt) (registry code 3260202) (OpenAirDocs)
- Registry engine: [Pratt & Whitney Canada PW118](https://openairdocs.org/engine/pratt-whitney-canada-pw118) (registry code 52116, turbo-prop) (OpenAirDocs)
- Category: Airplane
- Serial number: 120.221
- Airframe hours: 3928
- Engines: P&W PW-118A 1273 horsepower turbo prop
- Damage: No damage
- Flight: Part 135
- Operator: Mesa Airlines, Inc., doing business as United Express
- Registered owner: Chemical Trust Company Of Ca
- Airworthiness certificate: Standard, Transport
- Last inspection: Continuous airworthiness, July 20, 1992, 7 hours before
- Departed: DRO, DURANGO, CO
- Destination: DEN
- Flight plan: IFR
- Airport: DEN, Stapleton International, runway 26, 8,599 × 150 ft, concrete

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 34; airline transport, flight instructor, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 6,950 total, 179 in this make and model, 5,920 as pilot in command, 190 in the last 90 days, 100 in the last 30 days, 5 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 20° at 6 knots
- Visibility: 40 statute miles
- Lowest ceiling: none
- Temperature: 84 °F, dew point 54 °F
- Altimeter: 29.00 inHg

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Incident 19920721037959I](https://openairdocs.org/incident/19920721037959I), Jul 21, 1992: Emb EMB120RT, Denver, CO. Prop overspeed on both engines on approach. Landed safely. Found open circuit breakers for flight idle stop system.

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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