# NTSB ATL94IA088: Fokker F28 MK 0100, N890US, Charlotte, NC, May 1, 1994 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: May 1, 1994, 13:09 local (17:09 UTC) - Place: Charlotte, NC - Coordinates: 35.230014, -80.9104 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=35.2300&lon=-80.9104&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 94 uninjured - Status: Completed, report April 27, 1995 - Report: Approved by Office Director - NTSB case key (mKey): 3312 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ATL94IA088 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/3312/pdf - Page: https://openairdocs.org/ntsb/ATL94IA088 ## Probable cause THE IMPROPER RIGGING OF THE NOSE WHEEL STEERING SYSTEM BY COMPANY MAINTENANCE PERSONNEL. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Occurrence, landing - flare/touchdown - landing gear,steering system - incorrect (cause) - maintenance - improper, company maintenance personnel (cause) - landing gear,nose gear - jammed ## Analysis THE FLIGHTCREW REPORTED THAT WHILE EXTENDING THE LANDING GEAR, THE NOSE GEAR DID NOT INDICATE DOWN AND LOCKED. AFTER FURTHER ATTEMPTS TO LOWER THE NOSE GEAR WERE UNSUCCESSFUL, THE AIRCRAFT WAS LANDED WITH THE NOSE GEAR NOT DOWN AND LOCKED. INSPECTION REVEALED THAT THE NOSEWHEEL STEERING SYSTEM WAS INCORRECTLY RIGGED; THE NOSE GEAR WOULD NOT PROPERLY CENTER ITSELF, AND THE NOSEWHEEL STEERING CABLE TENSIONS WERE BELOW REQUIRED LIMITS. THIS RESULTED IN A SITUATION WHERE THE NOSE GEAR WOULD IMPINGE ON THE SIDE WALL OF THE GEAR WELL, PREVENTING EXTENSION. THE AIRCRAFT MANUFACTURER REPORTED THAT IT REQUIRED A COMBINATION OF NOSE GEAR MISRIGGING, WITH REDUCED CABLE TENSIONS, TO DUPLICATE THIS SCENARIO. ABOUT TWO WEEKS PRIOR TO THE INCIDENT, THE NOSEWHEEL STEERING CONTROL VALVE WAS REPLACED, WHICH WOULD HAVE REQUIRED A CHECK OF THE NOSE GEAR RIGGING. ## Factual narrative HISTORY OF FLIGHT On May 1, 1994, AT 1309 eastern daylight time, a Fokker F28 MK 100, N890US, landed without the nose landing gear extended at the Douglas International Airport, in Charlotte, North Carolina. Flight 323 was operated under the provisions of 14 CFR Part 121 by USAir, Inc., as a scheduled, domestic, passenger flight. The airline transport pilot and first officer, three flight attendants, and 89 passengers were not injured. There was minor damage to the airplane. Visual meteorological conditions existed at the time, and an instrument flight rules flight plan was filed for the flight to Charlotte. The flight originated in Detroit, Michigan at 1119. The flight crew reported the following: This was the third day of the three-day trip sequence, and the first day in this particular aircraft (N890US). On the day of the incident, the only flights flown by them were a flight to Detroit, and the flight to Charlotte (the incident flight). They reported no minimum equipment list entries regarding the landing gear system. There was an entry from the previous flight crew which stated that the nose wheel steering would occasionally bind while in operation. The nose wheel steering performed normally during the flight to Detroit, and the flight crew was not aware of any maintenance being performed on the aircraft in Detroit. The ground, takeoff, and enroute portions of the incident flight were normal. Approaching Charlotte, the flight was cleared for a visual approach to runway 18R. At 2,000 to 1,700 feet above ground level (agl), the landing gear handle was lowered. At approximately 1,300 feet agl, the main gear "snapped" into position. The nose gear indicated an "in transit" condition. They performed a missed approach, climbed to a higher altitude, and set the autopilot on. They attempted to recycle the gear, and again observed the "in transit" light on the nose gear, with the nose gear indicating that it was not down and locked. The first officer read the checklist, as the captain flew the airplane. The alternate landing gear extension checklist was performed, and the nose gear still did not indicate down and locked. The partial gear checklist was read, and Air Traffic Control personnel informed them that the nose gear appeared to be up. The aircraft was landed on runway 18R, and an emergency evacuation was accomplished. The captain reported that the antiskid switch was on when the aircraft was landed. PERSONNEL INFORMATION Information on the captain is included in this report at the section titled "First Pilot Information." Information on the first officer is included in Supplement E, attached to this report. AIRCRAFT INFORMATION The nose wheel steering (NWS) system on this aircraft consists of the following main components (shown in figures 1, 2, and 3, attached to this report): - The steering handwheel (tiller), which is connected to the rudder interface unit (IFU) through cables. - The rudder pedals, which are connected to the rudder IFU through a lever on the rudder torque tube and a push-pull rod. - The rudder IFU, which controls the NWS control unit through cables. - The NWS control unit, which operates the steering control valve when there is a difference between the selected and actual steering angles. - A nose wheel steering shut off valve which, when closed by the energized solenoid, prevents hydraulic pressure and flow to the steering control valve, and thus prevents the nose gear turning tube from turning. - The steering control valve, which controls the steering motor, which in turn operates the nose landing gear (NLG) turning tube with the sliding member and nose wheels. - A position feedback cable, which controls the steering control valve via the nose wheel steering control unit, such that the steering motor stops operating when the nose wheels are in the selected position. - A centering mechanism, to center the NLG when the landing gear lever has been selected to the up position. An input in the NWS system can be given by the tiller (up to 76 degrees either side). The steering input is supplied via the IFU to the NWS control unit. The tiller can override rudder pedal steering commands. On the NWS control unit are the pulleys for the input cables (from the rudder IFU) and the position feedback cables (from the NLG turning tube). The pulley system controls the steering control valve through an idler bar. When there is a steering input, the idler bar starts to turn. When the idler bar moves, it gives an input to the steering control valve, which allows hydraulic pressure to the NLG steering motor. When the NLG starts to turn, the position feedback cables move pulleys A and B (which are connected to each other). As a result, the idler bar turns back to the neutral position. The steering control valve is back in the neutral position when the nose wheels are in the selected position. The centering mechanism centers the NLG after a gear up selection, through the use of a centering cam and cam rollers (see figure 3). When the NLG moves during steering, the feedback input moves the cam. From the moment the landing gear lever is selected to the up position (pressure in the up lines), the centering actuator is pressurized, and extends, pushing the cam against the cam follower, through rollers. When the nose wheels are not in the centered position, the cam and follower are not aligned, and the cam contacts the rollers as the centering actuator is extended. This gives an input to the steering control valve. Because the NWS system is still pressurized, the NLG moves to the centered position during retraction. Hydraulic pressure in the up lines maintains the NLG in the retracted and centered position during flight. From the moment the landing gear lever is selected to the down position, (1) an electrical circuit energizes the nose wheel steering shut off valve solenoid, and thus depressurizes the NWS system, and (2) the hydraulic up lines and thus the centering actuator are depressurized, and the centering actuator is retracted by spring force. This causes the cam to disengage from the cam follower, and deactivates the centering mechanism. Via ground flight switches and a time delay relay, the nose wheel steering shut off valve solenoid remains energized, and thus the nose wheel steering system remains depressurized, until five seconds after touchdown. The aircraft maintenance records revealed that on April 14, 1994, a leaking nosewheel steering control valve was found. The steering control valve was replaced on April 20, 1994, during scheduled maintenance. According to the Fokker 100 Aircraft Maintenance manual (Procedure 32-52-02, Steering Control Valve Removal/Installation), an operational test of the steering control valve (after replacement) includes two checks if the nose wheels return to the center position: the first after the hydraulic system is pressurized, and the second after the steering handwheel and thus the NLG has been turned left and right. An inspection of the aircraft maintenance records revealed that an incorrect procedure number was entered after the steering control valve was replaced. Procedure number 32-52-01 (Steering Shut-off Valve Removal and Installation) was entered instead of procedure number 32-52-02. The mechanic who performed the work reported that although procedure number 32-52-01 was entered in the records, he used procedure number 32-52-02, the correct procedure. It was noted that procedure number 32-52-01 calls for a visual inspection of the nose wheel operation to the center position, and does not require the use of the rigging indicator tool, as does procedure number 32-52-02. Two flights prior to the incident flight, the flight crew entered into the aircraft maintenance logbook that the nosewheel steering would occasionally bind, when turning. The corrective maintenance action was to lubricate the nose landing gear. During ## Aircraft - Registration: [N890US](https://openairdocs.org/deregistered/N890US-2005-07-08), registration cancelled 2005-07-08, S/N 11365, built 1991 (OpenAirDocs) - Reported make and model: FOKKER F28 MK 0100 (F28 MK 010) - Registry model: [Fokker F.28 MK 0100](https://openairdocs.org/model/fokker-f-28-mk-0100) (registry code 4990807) (OpenAirDocs) - Registry engine: [Rolls-Royce TAY-650-15](https://openairdocs.org/engine/rolls-royce-tay-650-15) (registry code 54557, turbo-fan) (OpenAirDocs) - Category: Airplane - Serial number: 11365 - Airframe hours: 5845 - Engines: Rolls-Royce TAY MK650-15 15100 lbs thrust turbo fan - Damage: Minor damage - Flight: Part 121 - Operator: Usair, Inc. - Registered owner: Usair, Inc. - Airworthiness certificate: Standard, Transport - Last inspection: AAIP, April 29, 1994, 10 hours before - Departed: DTW, DETROIT, MI - Destination: CLT, NC - Flight plan: IFR - Airport: CLT, Douglas International, runway 18R, 10,000 × 150 ft, concrete ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 41; flight engineer, airline transport, commercial, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 9,000 total, 1,000 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: 240° at 12 knots - Visibility: 25 statute miles - Lowest ceiling: none - Temperature: 82 °F, dew point 55 °F - Altimeter: 29.00 inHg - Observed at: CLT ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Incident 19940501020739I](https://openairdocs.org/incident/19940501020739I), May 1, 1994: Fokker F28MK0100, Charlotte, NC, Minor damage. Pilot landing with nose gear in up position. Found nose landing steering system was improperly rigged. From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.