Embraer EMB-120RT N270AS

Summary

On 5 April 1991 at about 19:51 local time, a Embraer EMB-120RT registered N270AS, operated by Atlantic Southeast Airlines, was involved in an accident near Brunswick, Georgia, United States. 23 people were on board and 23 died. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

5 April 1991 at 19:51

Classification

Accident

Location

Brunswick, Georgia, United States

Coordinates

31.1492, -81.4795

Aircraft

Embraer EMB-120RT

Registration

N270AS

Category

Airplane

Engines

2

Operator

Atlantic Southeast Airlines

Operating rule

Part 135: Air Taxi & Commuter

Purpose of flight

Unknown

Phase of flight

Not recorded

Route

Atlanta → Unknown

Aircraft damage

Destroyed

Weather

VMC

Light

Day

NTSB number

DCA91MA033

23 people died.

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)

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.