Accident Embraer EMB-120RT Brasilia N270AS,

ASN Wikibase Occurrence # 325792

Date:	Friday 5 April 1991
Time:	14:51
Type:	Embraer EMB-120RT Brasilia
Owner/operator:	Delta Connection
Registration:	N270AS
MSN:	120218
Year of manufacture:	1990
Total airframe hrs:	816 hours
Cycles:	845 flights
Engine model:	Pratt & Whitney Canada PW118
Fatalities:	Fatalities: 23 / Occupants: 23
Aircraft damage:	Destroyed, written off
Category:	Accident
Location:	3 km W of Brunswick-Glynco Jetport, GA (BQK) - United States of America
Phase:	Approach
Nature:	Passenger - Scheduled
Departure airport:	Atlanta-William B. Hartsfield International Airport, GA (ATL/KATL)
Destination airport:	Brunswick-Glynco Jetport, GA (BQK/KBQK)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
Atlantic Southeast Flight 2311 was scheduled initially for Embraer EMB-120RT Brasilia N228AS to depart at 13:24 EST. Because of mechanical problems an airplane change was made to N270AS. The flight departed Atlanta at 13:47 and arrived in the Brunswick area about 14:44. At 14:48 the flight was cleared for a visual approach to runway 07. The Embraer had just turned from base leg to final approach when the aircraft was seen to pitch up about 5 degrees and roll to the left until the wings were vertical. The airplane then nosed down into the ground, 9975 feet short of the runway.

The left propeller blade angle at the time of impact was about 3 degrees, which is below the range for normal flight. The right propeller blade angle was above the flight idle low pitch stop.
It was determined that the left propeller actuator did not respond to a PCU action to increase blade angle because the PCU quill spline teeth were severely worn and could not engage the transfer tube spline. The extreme and rapid wear of the nitrided quill spline teeth was the result of the sliding contact with the titanium nitrided surface of the transfer tube spline.
This harder titanium-nitrided coating on the transfer tube was selected by the manufacturer, Hamilton Standard, to improve manufacturing efficiency compared to the originally certificated nitrided transfer tube.

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."

Accident investigation: