What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Narrative: on December 26, 1995 mesaba records show extensive maintenance on fairchild SA-227 aircraft N159MC in the area of the elevator quadrant. During the maintenance, a mechanic following maintenance manual procedures, removed the upper elevator bolt and related hardware. With the quadrant removed and on a bench, another mechanic loosely installed the hardware back on the quadrant, so the hardware would not be lost. "Loosely installed" as used here means, the elevator bolt and related hardware were installed, with the self locking nut tightened manually only, it was not properly torqued. The self locking feature of the nut was deteriorated. The nut presented to FAA by mesaba, as the nut removed from N159MC could be run down on the bolt to the point where one thread extended beyond the nut. This position of the nut, with the deteriorated locking feature, hand tightened on the bolt, I.e. one thread showing past the nut, is close to the appearance of a nut installed with the proper torque. In contrast, a new nut could only be run down a few turns on the bolt. Subsequently, mechanics installed the quadrant, with the improperly installed stop bolt on the aircraft. An inspector, po ssibly because the nut appeared torqued, did not notice the improper installation. The elevator quadrant could not be removed in the manner specified by maintenance manual procedures. The procedures called for the upper elevator stop (bolt, nut , eccentric) to be removed, with the quadrant to be rotated down through the casting stop and then removed from the aircraft. Thickness of the quadrant material at the elevator stop bolt holes prevented rotation of the elevator quadrant through the narrower stop casting. Therefore, operator personnel removed the stop casting before removing the quadrant. In removing the quadrant by first removing the stop casting, its not necessary to remove the upper elevator stop hardware. Some operator personnel were aware of this, others were not. On December 28, 1995, 16 flights after the above maintenance, on the approach of flight 3237 (msp) (minneapolis)-bji (Bemidji, MN) into bji, the crew reported the aircraft pitched down excessively and the elevator could not be moved to full up by the control column. Subsequently the crew initiated a go-around and used power to control pitch for landing. Excessive descent rate and airspeed at landing resulted inheavy landing. Maintenance investigation found a worked out upper elevator stop bolt in the elevator quadrant prevented elevator movement from about neutral to full up. The bolt worked out about 2". Upon movement of the control column for up, the worked out bolt, moving upward with the elevator control quadrant contacted the underside of a stringer (the first stringer just above the related access panel on the right side of the vertical stabilizer). This contact prevented further movement of the elevator in the up direction. The bolt appears to be bent from this contact and force exerted by the crew when pulling the control column back. Mesaba completed a fleet campaign to check upper and lower elevator stop bolts and to replace the self locking nuts. They are working with fairchild to correct the maintenance manual, and are initiating and/or evaluating other corrective actions.
As the FAA filed it
NARRATIVE: ON DECEMBER 26, 1995 MESABA RECORDS SHOW EXTENSIVE MAINTENANCE ON FAIRCHILD SA-227 AIRCRAFT N159MC IN THE AREA OF THE ELEVATOR QUADRANT. DURING THE MAINTENANCE, A MECHANIC FOLLOWING MAINTENANCE MANUAL PROCEDURES, REMOVED THE UPPER ELEVATOR BOLT AND RELATED HARDWARE. WITH THE QUADRANT REMOVED AND ON A BENCH, ANOTHER MECHANIC LOOSELY INSTALLED THE HARDWARE BACK ON THE QUADRANT, SO THE HARDWARE WOULD NOT BE LOST. "LOOSELY INSTALLED" AS USED HERE MEANS, THE ELEVATOR BOLT AND RELATED HARDWARE WERE INSTALLED, WITH THE SELF LOCKING NUT TIGHTENED MANUALLY ONLY, IT WAS NOT PROPERLY TORQUED. THE SELF LOCKING FEATURE OF THE NUT WAS DETERIORATED. THE NUT PRESENTED TO FAA BY MESABA, AS THE NUT REMOVED FROM N159MC COULD BE RUN DOWN ON THE BOLT TO THE POINT WHERE ONE THREAD EXTENDED BEYOND THE NUT. THIS POSITION OF THE NUT, WITH THE DETERIORATED LOCKING FEATURE, HAND TIGHTENED ON THE BOLT, I.E. ONE THREAD SHOWING PAST THE NUT, IS CLOSE TO THE APPEARANCE OF A NUT INSTALLED WITH THE PROPER TORQUE. IN CONTRAST, A NEW NUT COULD ONLY BE RUN DOWN A FEW TURNS ON THE BOLT. SUBSEQUENTLY, MECHANICS INSTALLED THE QUADRANT, WITH THE IMPROPERLY INSTALLED STOP BOLT ON THE AIRCRAFT. AN INSPECTOR, PO SSIBLY BECAUSE THE NUT APPEARED TORQUED, DID NOT NOTICE THE IMPROPER INSTALLATION. THE ELEVATOR QUADRANT COULD NOT BE REMOVED IN THE MANNER SPECIFIED BY MAINTENANCE MANUAL PROCEDURES. THE PROCEDURES CALLED FOR THE UPPER ELEVATOR STOP (BOLT, NUT , ECCENTRIC) TO BE REMOVED, WITH THE QUADRANT TO BE ROTATED DOWN THROUGH THE CASTING STOP AND THEN REMOVED FROM THE AIRCRAFT. THICKNESS OF THE QUADRANT MATERIAL AT THE ELEVATOR STOP BOLT HOLES PREVENTED ROTATION OF THE ELEVATOR QUADRANT THROUGH THE NARROWER STOP CASTING. THEREFORE, OPERATOR PERSONNEL REMOVED THE STOP CASTING BEFORE REMOVING THE QUADRANT. IN REMOVING THE QUADRANT BY FIRST REMOVING THE STOP CASTING, ITS NOT NECESSARY TO REMOVE THE UPPER ELEVATOR STOP HARDWARE. SOME OPERATOR PERSONNEL WERE AWARE OF THIS, OTHERS WERE NOT. ON DECEMBER 28, 1995, 16 FLIGHTS AFTER THE ABOVE MAINTENANCE, ON THE APPROACH OF FLIGHT 3237 (MSP) (MINNEAPOLIS)-BJI (BEMIDJI, MN) INTO BJI, THE CREW REPORTED THE AIRCRAFT PITCHED DOWN EXCESSIVELY AND THE ELEVATOR COULD NOT BE MOVED TO FULL UP BY THE CONTROL COLUMN. SUBSEQUENTLY THE CREW INITIATED A GO-AROUND AND USED POWER TO CONTROL PITCH FOR LANDING. EXCESSIVE DESCENT RATE AND AIRSPEED AT LANDING RESULTED INHEAVY LANDING. MAINTENANCE INVESTIGATION FOUND A WORKED OUT UPPER ELEVATOR STOP BOLT IN THE ELEVATOR QUADRANT PREVENTED ELEVATOR MOVEMENT FROM ABOUT NEUTRAL TO FULL UP. THE BOLT WORKED OUT ABOUT 2". UPON MOVEMENT OF THE CONTROL COLUMN FOR UP, THE WORKED OUT BOLT, MOVING UPWARD WITH THE ELEVATOR CONTROL QUADRANT CONTACTED THE UNDERSIDE OF A STRINGER (THE FIRST STRINGER JUST ABOVE THE RELATED ACCESS PANEL ON THE RIGHT SIDE OF THE VERTICAL STABILIZER). THIS CONTACT PREVENTED FURTHER MOVEMENT OF THE ELEVATOR IN THE UP DIRECTION. THE BOLT APPEARS TO BE BENT FROM THIS CONTACT AND FORCE EXERTED BY THE CREW WHEN PULLING THE CONTROL COLUMN BACK. MESABA COMPLETED A FLEET CAMPAIGN TO CHECK UPPER AND LOWER ELEVATOR STOP BOLTS AND TO REPLACE THE SELF LOCKING NUTS.THEY ARE WORKING WITH FAIRCHILD TO CORRECT THE MAINTENANCE MANUAL, AND ARE INITIATING AND/OR EVALUATING OTHER CORRECTIVE ACTIONS.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.
Other reports on N159MC · 5
Matched to the same aircraft by N-number and date.