# NTSB DCA91MA033: Embraer EMB-120RT, N270AS, Brunswick, GA, April 5, 1991

- Type: NTSB accident investigation
- Classification: Accident · Fatal · Class 1 · Major · Final report
- Date: April 5, 1991, 14:51 local (19:51 UTC)
- Place: Brunswick, GA
- Coordinates: 31.149225, -81.479545 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=31.1492&lon=-81.4795&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Highest injury: Fatal
- Injuries: 23 fatal
- Status: Completed, report August 5, 1993
- Report: Board-adopted at Board Meeting
- Investigation class: Class 1
- NTSB office: Major Investigations Division
- Safety recommendations: Yes
- NTSB case key (mKey): 15951
- NTSB case page: https://www.ntsb.gov/investigations/Pages/DCA91MA033.aspx
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/15951/pdf
- Board report AAR9203 (PDF): https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR9203.pdf
- Page: https://openairdocs.org/ntsb/DCA91MA033

## Probable cause

THE LOSS OF CONTROL IN FLIGHT AS A RESULT OF A MALFUNCTION OF THE LEFT ENGINE PROPELLER CONTROL UNIT WHICH ALLOWED THE PROPELLER BLADE ANGLES TO GO BELOW THE FLIGHT IDLE POSITION. CONTRIBUTING TO THE ACCIDENT WAS THE DEFICIENT DESIGN OF THE PROPELLER CONTROL UNIT BY HAMILTON STANDARD AND THE APPROVAL OF THE DESIGN BY THE FEDERAL AVIATION ADMINISTRATION. THE DESIGN DID NOT CORRECTLY EVALUATE THE FAILURE MODE THAT OCCURRED DURING THIS FLIGHT, WHICH RESULTED IN AN UNCOMMANDED AND UNCORRECTABLE MOVEMENT OF THE BLADES OF THE AIRPLANE'S LEFT PROPELLER BELOW THE FLIGHT IDLE POSITION. (NTSB REPORT AAR-92/03)

## Sequence of events

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

- Airframe/component/system failure/malfunction, approach
  - propeller system/accessories,prop control unit - inadequate (cause)
  - acft/equip,inadequate design, manufacturer (contributing factor)
  - inadequate substantiation process, faa(organization) (contributing factor)
  - propeller system/accessories,prop control unit - failure,partial (cause)
- Loss of control - in flight, approach
- In flight collision with terrain/water, approach

## Analysis

WITNESSES REPORTED THAT THE AIRPLANE SUDDENLY TURNED OR ROLLED LEFT UNTIL THE WINGS WERE PERPENDICULAR TO THE GROUND. THE AIRPLANE THEN FELL IN A NOSE-DOWN ATTITUDE. EXAM OF THE LEFT PROP COMPONENTS INDICATED A BLADE ANGLE OF ABOUT 3 DEG, WHILE THE LEFT PROP CONTROL UNIT (PCU) BALLSCREW POSITION WAS CONSISTENT WITH A COMMANDED BLADE ANGLE OF 79.2 DEG. EXTREME WEAR ON THE PCU QUILL SPLINE TEETH, WHICH NORMALLY ENGAGED THE TITANIUM-NITRIDED SPLINES OF THE PROP TRANSFER TUBE, WAS FOUND. THE TITANIUM-NITRIDED SURFACE WAS MUCH HARDER AND ROUGHER THAN THE NITRIDED SURFACE OF THE QUILL. THEREFORE, THE TRANSFER TUBE SPLINES ACTED LIKE A FILE AND CAUSED ABNORMAL WEAR OF THE GEAR TEETH ON THE QUILL. WEAR OF THE QUILL WAS NOT CONSIDERED DURING THE CERTIFICATION OF THE PROPELLER SYSTEM.

## Aircraft

- Registration: [N270AS](https://openairdocs.org/deregistered/N270AS-1991-07-30), registration cancelled 1991-07-30, S/N 120218 (OpenAirDocs)
- Reported make and model: EMBRAER EMB-120RT
- Registry model: [Embraer EMB-120RT](https://openairdocs.org/model/embraer-emb-120rt) (registry code 3260202) (OpenAirDocs)
- Category: Airplane
- Serial number: 120-218
- Airframe hours: 816
- Engines: P&W PW-118 1800 horsepower turbo prop
- Damage: Destroyed
- Fire: On-Ground
- Flight: Part 135
- Operator: Atlantic Southeast Airlines
- Airworthiness certificate: Standard, Transport
- Last inspection: Continuous airworthiness, April 1, 1991, 26 hours before
- Departed: ATL, ATLANTA, GA
- Flight plan: IFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 34; airline transport, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; toxicology performed; flight hours: 11,724 total, 5,720 in this make and model

## Weather

- Conditions: Visual (VMC), Day
- Wind: 160° at 10 knots
- Visibility: 7 statute miles
- Lowest ceiling: 10,000 ft broken
- Temperature: 79 °F, dew point 70 °F
- Altimeter: 30.00 inHg
- Observed at: BQK, 2 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 19910405009019A](https://openairdocs.org/incident/19910405009019A), Apr 5, 1991: Emb EMB120RT, Brunswick, GA, Destroyed, 23 fatal. Severe asymmetric thrust on final approach caused loss of control. Result of left propeller control unit malfunction

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.

---
OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.