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."
Loss of control
Radar data
Hamilton Standard propeller system Model 14RF
| Status: | Accident investigation report completed and information captured |
| Date: | Friday 5 April 1991 |
| Time: | 14:51 |
| Type: |  Embraer EMB-120RT Brasilia |
| Operated by: | Atlantic Southeast Airlines - ASA |
| On behalf of: | Delta Connection |
| Registration: | N270AS |
| MSN: | 120218 |
| First flight: | 1990 |
| Total airframe hrs: | 816 |
| Cycles: | 845 |
| Engines: | 2 Pratt & Whitney Canada PW118 |
| Crew: | Fatalities: 3 / Occupants: 3 |
| Passengers: | Fatalities: 20 / Occupants: 20 |
| Total: | Fatalities: 23 / Occupants: 23 |
| Aircraft damage: | Destroyed |
| Aircraft fate: | Written off (damaged beyond repair) |
| Location: | 3 km (1.9 mls) W of Brunswick-Glynco Jetport, GA (BQK) ( United States of America)
|
| Phase: | Approach (APR) |
| Nature: | Domestic Scheduled Passenger |
| Departure airport: | Atlanta-William B. Hartsfield International Airport, GA (ATL/KATL), United States of America |
| Brunswick-Glynco Jetport, GA (BQK/KBQK), United States of America | |
| Flightnumber: | 2311 |
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:
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:
 |
|
Classification:
Engine reverse issue Loss of control
Sources:
» NTSB/AAR-92/03Follow-up / safety actions
NTSB issued 6 Safety Recommendations
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Photos
Radar data
Hamilton Standard propeller system Model 14RF
Video, social media
Map
This map shows the airport of departure and the intended destination of the flight. The line between the airports does not display the exact flight path.
Distance from Atlanta-William B. Hartsfield International Airport, GA to Brunswick-Glynco Jetport, GA as the crow flies is 381 km (238 miles).
Accident location: Exact; as reported in the official accident report.
Distance from Atlanta-William B. Hartsfield International Airport, GA to Brunswick-Glynco Jetport, GA as the crow flies is 381 km (238 miles).
Accident location: Exact; as reported in the official accident report.
This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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Embraer EMB-120
- 357 built
- 4th loss
- 4th fatal accident
- The worst accident (at the time)
- 3rd worst accident (currently)
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