Individually Owned: 150,657
Corporate Owned: 137,281
Aircraft Accident/Incident Report
Atlanta, Georgia 30320
Sunday, November 11, 1990 18:10 EST
NTSB Narrative Summary Released at Completion of Accident
DURING DESCENT THE AFCAS STABILIZER TRIM & AUTOPILOT DISENGAGED. BOTH WERE RESET WITH A 2ND DISENGAGEMENT. NOSE DOWN CONTROL PRESSURES WERE ENCOUNTERED & THE FLT CREW ATTEMPTED TO USE MANUAL TRIM, FOLLOWED BY A JAMMED STABILIZER MASTER WARNING. AFCAS STABILIZER TRIM WAS LEFT OFF IAW ABNORMAL PROCEDURES. FDR DATA SHOWED THE STAB THEN CREEPED TO A FULL ACFT NOSE DOWN POSITION & HYD PRES TO THE STAB ACTUATOR WAS AUTOMATICALLY REMOVED, PER DESIGN. SUBSEQUENT TESTING OF THE HORIZONTAL STABILIZER CONTROL UNIT ASSEMBLY SHOWED THAT, AFTER SPRAYING THE SERVO VALVE WITH WATER AND COLD SOAKING, ICE WOULD FORM INSIDE THE END CAP AND A JAMMED SERVO VALVE CONDITION WOULD OCCUR. THE END CAP AND SPRING EXHIBITED SUBSTANTIAL RUST CORROSION. CREW MOVEMENT OF THE MANUAL TRIM RESULTED IN THE JAMMED STAB WARNING.
NTSB Probable Cause Narrative
FROZEN MOISTURE IN THE STABILIZER ACTUATOR HYDRAULIC SERVO VALVE WHICH RESULTED IN REDUCED MOVEMENT OF THE SERVO VALVE AND LIMITED ITS ABILITY TO RESPOND TO FLIGHT CONTROL INPUTS. THE LACK OF RESPONSE FROM THE SERVO VALVE RESULTED IN THE JAMMED STABILIZER MESSAGE. A FACTOR WAS THE INADEQUATE DESIGN OF THE SERVO VALVE WHICH PRECLUDED MOISTURE DRAINAGE.
Event Information
| Type of Event | Incident |
| Event Date | 11/11/1990 |
| Event Day of the Week | Sunday |
| Time of Event | 1810 |
| Event Time Zone | Eastern Standard Time |
| Event City | ATLANTA |
| Event State | GEORGIA |
| Event Country | -- |
| Zipcode of the event site | 30320 |
| Event Date Year | 1990 |
| Event Date Month | 11 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | |
| Event Location Longitude | |
| Event Location Airport | |
| Event Location Nearest Airport ID | |
| Indicates whether the acc/inc occurred off or on an airport | Off Airport/Airstrip |
| Distance from airport in statute miles | 0 |
| Degrees magnetic from airport | 0 |
| Airport Elevation | 0 |
| Weather Briefing Completeness | Full |
| Investigator's weather source | Weather Observation Facility |
| Time of the weather observation | 1750 Eastern Standard Time |
| Direction of event from weather observation facility (degrees) | 0 |
| Weather Observation Facility ID | ATL |
| Elevation of weather observation facility | 1026 |
| Distance of event from weather observation facility (units?) | 0 |
| Time Zone of the weather observation | EST |
| Lighting Conditions | Dusk |
| Lowest Ceiling Height | 0 |
| Lowest Non-Ceiling Height | 0 |
| Sky/Lowest/Cloud Conditions | Clear |
| Sky Condition for Lowest Ceiling | None |
| Visibility Runway Visual Range (Feet) | 0 |
| Visibility Runway Visual Value (Statute Miles) | 0 |
| Visibility (Statute Miles) | 20 |
| Air Temperature at event time (in degrees celsius) | 16 |
| Dew Point at event time (in degress fahrenheit) | 4 |
| Wind Direction (degrees magnetic) | 300 |
| Variable Wind Indicator | Unknown |
| Wind Speed (knots) | 4 |
| Wind Velocity Indicator | Unknown |
| Wind Gust Indicator | Not Gusting |
| Wind Gust (knots) | 0 |
| Altimeter Setting at event time (in. Hg) | 30 |
| Density Altitude (feet) | 800 |
| Intensity of Precipitation | Unknown |
| 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 | 75 |
| Injury Total Serious | -- |
| Injury Total All | -- |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 5051 |
| NTSB Notification Source | -- |
| NTSB Notification Date | Nov 11 1990 12:00AM |
| NTSB Notification Time | 1910 |
| Fiche Number and/or location -used to find docket information | 45538 |
| Date of most recent change to record | Dec 12 2000 5:33PM |
| User who most recently changed record | dbo |
| Basic weather conditions | Visual Meteorological Cond |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N850US |
| NTSB Number | ATL91IA017 |
| Missing Aircraft Indicator | N |
| Federal Aviation Reg. Part | Part 121: Air Carrier |
| Type of Flight Plan filed | IFR |
| Flight plan Was Activated? | -- |
| Damage | None |
| Aircraft Fire | None |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | FOKKER |
| Aircraft Model | F28 MK0100 |
| Aircraft Series Identifier | F28 MK0100 |
| Aircraft Serial Number | 11276 |
| Certified Max Gross Weight | 98100 |
| 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 | 109 |
| Number of Engines | 2 |
| Fixed gear or retractable gear | Retractable |
| Aircraft, Type of Last Inspection | Continuous Airworthiness |
| Date of Last Inspection | Oct 10 1990 12:00AM |
| Airframe hours since last inspection | 147 |
| Airframe Hours | 2674 |
| ELT Installed | No |
| ELT Activated | No |
| ELT Aided Location of Event Site | No |
| ELT Type | -- |
| Aircraft Owner Name | |
| Aircraft Owner Street Address | |
| Aircraft Owner City | |
| Aircraft Owner State | |
| Aircraft Owner Country | |
| Aircraft Owner Zipcode | |
| Operator is an individual? | -- |
| Operator Name | USAIR |
| Operator Same as Owner? | No |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | No |
| Operator Street Address | 2345 CRYSTAL PARK DRIVE |
| Operator City | ARLINGTON |
| Operator State | VA |
| Operator Country | |
| Operator Zip code | 22227 |
| Operator Code | USAA |
| Owner has at least one certificate | Yes - certificate holder |
| Other Operator of large aircraft? | No |
| Certified for Part 133 or 137 Operation | Unknown |
| 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 | PHL |
| Departure City | PHILADELPHIA |
| Departure State | PA |
| Departure Country | |
| Departure Time | 1632 |
| Departure Time Zone | EST |
| Destination Same as Local Flt | -- |
| Destination Airport Code | ATL |
| Destination City | ATLANTA |
| Destination State | GA |
| Destination Country | |
| Specific Phase of Flight | Descent |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | Jan 2 2001 10:30AM |
| User who most recently changed record | dbo |
| Since inspection or accident | -- |
| Event Location Runway Number and Location | 0 |
| Runway Length | 0 |
| Runway Width | 0 |
| Sight Seeing flight | No |
| Air Medical Flight | No |
| Medical Flight | -- |