Individually Owned: 150,657
Corporate Owned: 137,281
Fresno-Yosemite International Airport
Aircraft Accident/Incident Report
Fresno, California 93727
Monday, February 21, 2000 9:58 PST
NTSB Narrative Summary Released at Completion of Accident
The elevator trim froze in flight. During the initial descent from 22,000 feet mean sea level (msl) to 14,000 feet msl, the trim wheel moved to the forward stop. The trim wheel made a "snapping" motion midway through the movement, and then moved aft. The trim wheel continued to move back and forth, so the crew disconnected the autopilot and trim. The airplane wanted to pitch up, and the captain had to apply moderate forward pressure to maintain pitch control. The trim wheel was still jammed, but one crewmember could control the airplane. At 12,000 feet msl, and approximately 23 degrees Fahrenheit outside air temperature, the trim remained immovable. Between 5,000 feet msl and 4,000 feet msl, the trim wheel became moveable. By the time the airplane reached the traffic pattern altitude, the trim wheel moved freely. The outside temperature at that time was 46 degrees Fahrenheit. Examination of the elevator trim units revealed that one trim actuator had leaking shaft seals. Its packing had cracked, and a bearing had seized. The second actuator was dirty, and minor corrosion was on the hardware. The shaft seals leaked, and a rigging device was installed. Service Difficulty Report (SDR) data from August 30, 1990, to February 29, 2000, contained 19 reports of the elevator trim freezing at altitude. Nine of the reports noted that the trim operated normally after descent to lower altitudes and warmer temperatures. Eleven additional reports referenced binding or stiffness at altitude. Some of the airplanes experienced multiple events. During some of the events, the airplane pitched violently. The manufacturer discovered moisture and corrosion in some of the actuators that were submitted for repair after these occurrences. They suspected that leaking seals allowed moisture into the actuators, which froze at altitude. They developed a modification that included installation of additional seals inside the actuator. However, Skywest maintenance records indicate that both unmodified (Part Number 5299) and modified (Part Number 5299-1) actuators experienced problems. Both actuators on the incident airplane were unmodified units. Total time on the airplane was 3,757 hours.
NTSB Probable Cause Narrative
Moisture contamination of the elevator trim actuator units resulting in their failure to operate at below freezing temperatures
Event Information
| Type of Event | Incident |
| Event Date | 2/21/2000 |
| Event Day of the Week | Monday |
| Time of Event | 958 |
| Event Time Zone | Pacific Standard Time |
| Event City | FRESNO |
| Event State | CALIFORNIA |
| Event Country | -- |
| Zipcode of the event site | 93727 |
| Event Date Year | 2000 |
| Event Date Month | 2 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | 363430N |
| Event Location Longitude | 1190530W |
| Event Location Airport | Fresno-Yosemite International |
| Event Location Nearest Airport ID | KFAT |
| Indicates whether the acc/inc occurred off or on an airport | Off Airport/Airstrip |
| Distance from airport in statute miles | -- |
| Degrees magnetic from airport | -- |
| Airport Elevation | -- |
| Weather Briefing Completeness | Full |
| Investigator's weather source | Weather Observation Facility |
| Time of the weather observation | 958 Pacific Standard Time |
| Direction of event from weather observation facility (degrees) | 0 |
| Weather Observation Facility ID | FAT |
| Elevation of weather observation facility | 0 |
| Distance of event from weather observation facility (units?) | 0 |
| Time Zone of the weather observation | PST |
| Lighting Conditions | Day |
| Lowest Ceiling Height | -- |
| Lowest Non-Ceiling Height | 5000 |
| Sky/Lowest/Cloud Conditions | Scattered |
| Sky Condition for Lowest Ceiling | None |
| Visibility Runway Visual Range (Feet) | 0 |
| Visibility Runway Visual Value (Statute Miles) | 0 |
| Visibility (Statute Miles) | 10 |
| Air Temperature at event time (in degrees celsius) | 15 |
| Dew Point at event time (in degress fahrenheit) | 7 |
| Wind Direction (degrees magnetic) | 120 |
| Variable Wind Indicator | Wind direction could be determined |
| Wind Speed (knots) | 9 |
| Wind Velocity Indicator | -- |
| Wind Gust Indicator | Not Gusting |
| Wind Gust (knots) | -- |
| Altimeter Setting at event time (in. Hg) | 29 |
| Density Altitude (feet) | -- |
| Intensity of Precipitation | -- |
| METAR weather report | -- |
| Event Highest Injury | None |
| On Ground, Fatal Injuries | 0 |
| On Ground, Minor Injuries | 0 |
| On Ground, Serious Injuries | 0 |
| Injury Total Fatal | -- |
| Injury Total Minor | -- |
| Injury Total None | 20 |
| Injury Total Serious | -- |
| Injury Total All | -- |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 15289 |
| NTSB Notification Source | -- |
| NTSB Notification Date | Feb 21 2000 12:00AM |
| NTSB Notification Time | 1443 |
| Fiche Number and/or location -used to find docket information | DMS |
| Date of most recent change to record | Apr 28 2004 3:34PM |
| User who most recently changed record | NTSB\MONR |
| Basic weather conditions | Visual Meteorological Cond |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N566SW |
| NTSB Number | LAX00IA106 |
| Missing Aircraft Indicator | N |
| Federal Aviation Reg. Part | Part 121: Air Carrier |
| Type of Flight Plan filed | IFR |
| Flight plan Was Activated? | Yes |
| Damage | None |
| Aircraft Fire | None |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | Embraer |
| Aircraft Model | 120 |
| Aircraft Series Identifier | 120 |
| Aircraft Serial Number | 120341 |
| Certified Max Gross Weight | 26433 |
| Aircraft Category | Airplane |
| Aircraft Registration Class | U.S. Registered/U.S. Soil |
| Aircraft is a homebuilt? | No |
| Flight Crew Seats | -- |
| Cabin Crew Seats | -- |
| Passenger Seats | -- |
| Total number of seats on the aircraft | 33 |
| Number of Engines | 2 |
| Fixed gear or retractable gear | Retractable |
| Aircraft, Type of Last Inspection | Continuous Airworthiness |
| Date of Last Inspection | Feb 19 2000 12:00AM |
| Airframe hours since last inspection | 18 |
| Airframe Hours | 3768.4 |
| ELT Installed | Yes |
| ELT Activated | No |
| ELT Aided Location of Event Site | No |
| ELT Type | -- |
| Aircraft Owner Name | SKYWEST AIRLINES, INC. |
| Aircraft Owner Street Address | 444 RIVER ROAD |
| Aircraft Owner City | ST. GEORGE |
| Aircraft Owner State | UT |
| Aircraft Owner Country | USA |
| Aircraft Owner Zipcode | 84770 |
| Operator is an individual? | No |
| Operator Name | -- |
| Operator Same as Owner? | Yes |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | Yes |
| Operator Street Address | -- |
| Operator City | -- |
| Operator State | -- |
| Operator Country | -- |
| Operator Zip code | -- |
| Operator Code | SWIA |
| Owner has at least one certificate | -- |
| Other Operator of large aircraft? | -- |
| Certified for Part 133 or 137 Operation | -- |
| Operator Certificate Number | -- |
| Indicates whether an air carrier operation was scheduled or not | Scheduled |
| Indicates Domestic or International Flight | Domestic |
| Operator carrying Pax/Cargo/Mail | Passenger Only |
| Type of Flying (Per_Bus / Primary) | Unknown |
| Second Pilot on Board | Yes |
| Departure Point Same as Event | No |
| Departure Airport Code | LAX |
| Departure City | LOS ANGELES |
| Departure State | CA |
| Departure Country | USA |
| Departure Time | 0 |
| Departure Time Zone | PST |
| Destination Same as Local Flt | -- |
| Destination Airport Code | FAT |
| Destination City | Fresno-Yosemite |
| Destination State | CA |
| Destination Country | USA |
| Specific Phase of Flight | Cruise |
| Report sent to ICAO? | -- |
| Evacuation occurred | No |
| Date of most recent change to record | Feb 3 2004 4:20PM |
| User who most recently changed record | COOS |
| Since inspection or accident | -- |
| Event Location Runway Number and Location | NA |
| Runway Length | -- |
| Runway Width | -- |
| Sight Seeing flight | No |
| Air Medical Flight | No |
| Medical Flight | -- |