- Date
- November 11, 1990, 18:10 local (23:10 UTC)
- Place
- Atlanta, GA
- Injuries
- 75 uninjured
- Damage
- No damage
- Phase of flight
- Enroute
- Aircraft
- N850USFokker F28 MK0100
- Weather
- Visual (VMC) · Dusk
- Status
- Completed · report May 10, 1993
- Report
- Approved by Office Director
- FAA report
- 19901111057209I
- Case key
- 8341
From the NTSB’s public API. By law, NTSB reports can’t be used as evidence in lawsuits over the incident.
On this page
Probable cause
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.
Sequence of events
NTSB’s coding before 2008: each occurrence and phase of flight, and the causes and factors under it. The codes are defined in NTSB’s coding manual.
Analysis
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.
Aircraft
- Registration
- N850US
- Reported as
- Fokker F28 MK0100
- Category
- Airplane
- Serial number
- 11276
- Airframe hours
- 2,674
- Engine
- Rolls-Royce TAY650715, 15,000 lbs thrust, turbo jet
- Damage
- No damage
- Flight
- Part 121
- Operator
- Usair
- Airworthiness certificate
- Standard, Transport
- Last inspection
- Continuous airworthiness · October 10, 1990 · 147 hours before
- Departed
- PHL · Philadelphia, PA
- Destination
- ATL · Atlanta, GA
- Flight plan
- IFR
Matched to the registry by N-number and the event date; the registry’s history has gaps, so older matches can be wrong. Compare the reported make and model.
Flight crew
As NTSB recorded them. NTSB leaves out names.
- Role
- Pilot
- Age
- 41
- Certificate
- Airline transport
- Airplane ratings
- Multi-engine land
- Instrument ratings
- Airplane
- Medical
- Class 1, Valid Medical--no waivers/lim.
- Seat
- Left
- Flight hours
- 15,127 total
Weather
- Conditions
- Visual (VMC) · Dusk
- Wind
- 300° at 4 knots
- Visibility
- 20 statute miles
- Lowest ceiling
- None
- Temperature
- 61 °F, dew point 39 °F
- Altimeter
- 30.00 inHg
- Observed at
- ATL
FAA reports on this event · 1
The FAA’s own accident and incident reports, matched to the aircraft by N-number and date.