Date: 201505
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Aircraft: MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Aircraft component: Horizontal Stabilizer Trim
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Technician
Human factors: Troubleshooting; Situational Awareness; Fatigue
Second reporter function: Technician
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
When detected: Other Maintenance Personnel
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Aircraft had been placed AOG (aircraft on ground) after landing. Pilot stated that horizontal stabilizer was in a runaway nose down position and felt heavy during landing. Another mechanic and I were sent to repair the aircraft and make serviceable. When we landed we got a turnover from the pilot and reviewed the logbook write up. Once we reviewed everything we attempted to operate the stabilizer primary trim system and try and duplicate the fault; during the operation of the stabilizer primary trim we discovered the trim was no longer on a runaway nose down and in fact would operate normally in the nose down position; however it would not operate in a nose up position. Contract maintenance personnel that had been on the aircraft when it landed confirmed the pilot's original defect of a runaway nose down situation. My partner and I agreed we would replace the primary trim motor as our first step; when we opened the packaging with the new trim motor we realized it had been removed as a serviceable unit from another aircraft and was missing half the gasket needed between the motor and the gearbox assembly. We notified maintenance control of the missing gasket and all agreed we would install the motor with the used gasket for troubleshooting purposes and verify if that would be a positive fix; maintenance control agreed to order a gasket AOG and concurred with the installation of the motor; which was carried out per the aircraft maintenance manual using the old gasket and documented into the aircraft logbook. The access panel that was removed in order to access the trim motor; referred to as the 'doghouse'; remained off the aircraft during the troubleshooting for the remainder of the day. Once the motor was installed; we ops checked the system and found the fault was not fixed; all that occurred was that now we could actuate the stabilizer trim approximately 1/8' and it would return approximately 1/16'. We contacted maintenance control and stated our find and we agreed we would leave the motor installed and wait for the gasket to arrive the following morning. We continued to troubleshoot the system into the night. Prior to our duty time reaching 16 hrs we contacted maintenance control and gave a pass down of what had been accomplished for the day and agreed we would install the 'doghouse' panel to protect the motor and metal structure from the elements and temp secure it so as to allow quick access in the morning for the replacement of the gasket. The following morning when we arrived at the aircraft we contacted maintenance control as requested to notify them we were on the aircraft; and were asked to continue troubleshooting the system; at which point we followed the troubleshooting tree; and performed power checks at the primary nose up contactor; where power was confirmed to be found. In order to find power this required us to move the stabilizer nose up and nose down and no damage occurred during this time. Once we confirmed the presence of power at the contactor; we replaced the primary nose up contactor and performed an ops check of the stabilizer and found the fault to remain. We contacted maintenance control to report our progress; it was at this time we were asked by the maintenance controller to inspect the jackscrew assembly. Due to the fact the stabilizer was in a nose up position; we needed to move the stabilizer into a nose down position. During the movement of the stabilizer nose down position past the 0 detent we heard a noise and stopped the movement of the stabilizer. We looked around for the culprit of the noise and found nothing so continued to slowly move the stabilizer nose down; once it reached a 1 detent; we heard and felt the aircraft jump; at this point I realized the culprit was the stabilizer and believed the jackscrew had been damaged. Once I exited the aircraft and looked towards the tail section I immediately realized the 'doghouse' panel had been forcefully dislodged from the aircraft. I put on asafety harness and went to assess the damage and see what had caused the damage. Once I reached the horizontal stabilizer I realized the right elevator fairing had managed to lodge itself into the 'doghouse' panel and then be crushed by the panel while forcing it to come off the structure and ripping the screws securing it out. Once I assessed the damage we notified maintenance control of the incident along with my supervisor on duty; and was told to take detailed pictures of the damage and submit them to maintenance control along with a written statement of the incident.Only preventative measure I can think of is that we should have secured the doghouse panel with all the required screws; gone to the hotel and gotten some rest and the next morning first thing should have been remove the doghouse panel and installed the gasket before continuing the troubleshooting of the system.


Second narrative: [Report contained no additional information.]


Synopsis: Two Maintenance Technicians reported that while moving the stabilizer on an MD80 for troubleshooting; it contacted and damaged the 'Dog House' panel because the panel was not properly secured.