Accident Embraer EMB-120ER Brasilia N288SW, Sunday 25 February 2001
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Date:Sunday 25 February 2001
Time:23:55 LT
Type:Silhouette image of generic E120 model; specific model in this crash may look slightly different    
Embraer EMB-120ER Brasilia
Owner/operator:Skywest Airlines
Registration: N288SW
MSN: 120316
Total airframe hrs:11650 hours
Engine model:Pratt & Whitney Canada PW-118B
Fatalities:Fatalities: 0 / Occupants: 33
Other fatalities:0
Aircraft damage: None
Category:Accident
Location:Monterey Regional Airport, CA (MRY/KMRY) -   United States of America
Phase: Unknown
Nature:Passenger - Scheduled
Departure airport:Los Angeles International Airport, CA (LAX/KLAX)
Destination airport:Monterey Regional Airport, CA (MRY/KMRY)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
Narrative:
The lone cabin attendant in the aft end of the airplane sustained a broken ankle when she was thrown to the floor after the airplane experienced an abrupt pitch change during descent. The captain had the autopilot engaged as the airplane descended through 10,000 feet mean sea level. The nose pitched down violently about 10 degrees, and then the nose pitched back up. The captain disengaged the autopilot and hand flew the airplane to touchdown. The Brasilia has two elevator trim actuators. The manufacturer discovered moisture and corrosion in some of the actuators submitted for repair after similar occurrences. They suspected that leaking seals allowed moisture into the actuators, which froze at altitude. In numerous instances, the actuators functioned properly after descent to lower altitudes and warmer temperatures, where the units thawed. One unit was dirty, corroded, and had overspray on it. It leaked from the shaft seals and autoloc seal. It failed the non-jamming stop test. It's two shaft housings contained moisture. The chain and pins were corroded, the packing had deteriorated, and the springs were weak. One side of the rollers was not chamfered, and staking warped some screws. The hub was worn and not functioning properly. The second unit was dirty and had overspray on it. The actuator leaked from the shaft seals. The actuator had excessive backlash and failed the tangential free play test. It's two shaft housings contained moisture. The chain, pins, shafts, and housings were corroded. The packing had deteriorated, and the bearings were rough and binding. The rollers only had one chamfered side. The shim was not with the unit.

Probable Cause: moisture contamination of the elevator trim actuators, which allowed the units to freeze at altitude resulting in an abrupt pitch change when the units thawed at lower altitudes.

Accident investigation:
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Investigating agency: NTSB
Report number: LAX01LA105
Status: Investigation completed
Duration: 3 years 1 month
Download report: Final report

Sources:

NTSB LAX01LA105

Location

Revision history:

Date/timeContributorUpdates
25-Mar-2024 11:26 ASN Update Bot Added

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