DC-10 Undifferentiated or Other Model
Maintenance Airframe; Maintenance Powerplant
Confusion; Troubleshooting; Situational Awareness; Communication Breakdown
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Other / Unknown
Aircraft Aircraft Damaged; General Maintenance Action
Aircraft; Human Factors; MEL
DC-10 aircraft had an inbound write-up for '#3 THRUST REVERSER WOULD NOT UNLOCK U/L TURNS AMBER; BUT NOT GREEN. REV 3 PRESS FAULT ILLUMINATES.'  Was unable to determine cause of malfunction and deferred Number 3 Thrust Reverser using MEL 78-30-01.  Step-6 of MEL 'Install Lockout Tool in both Right and Left Center Gearbox unused pads of Fan Reverser.'  Was complied with (c/w) under the fan cowls.  Step-7: 'Tag and mark each deactivation tool to indicate the tool must be removed prior to system activation.' Was interpreted as meaning to install the red 'DO NOT OPERATE' 'signal plates' on the outside of the Thrust Reverser as a visual indicator that the lockout tool has been installed; the reverser has been locked out and the thrust reverser can't be deployed.  From reading the write up and Maintenance entries; the ZZZ1 AMT's reactivated the thrust reverser for troubleshooting; the external red 'DO NOT OPERATE' 'signal plates' were not removed and the thrust reverser was damaged during deployment.    [Contributors are] Human error and inconsistencies in procedures.  ALL of our CF6 Thrust Reverser MELs [for our other fleets] call out [for] the installation of the 'stow bolts' and red 'DO NOT OPERATE' 'signal/warning plates;' EXCEPT the DC-10.  Conversely; none of our CF6 Thrust Reverser MELs use the verbiage 'Tag and mark each deactivation tool to indicate the tool must be removed prior to system activation;' EXCEPT the DC10.  All of our CF6 Engine Thrust Reversers use a similar deactivation tool that is inverted on the Center Drive Actuator Unit (CDU) and remains with the aircraft.  Since all other CF6 thrust reversers require 'stow bolts'; red 'DO NOT OPERATE'; 'signal/warning plates' and the exact same red 'DO NOT OPERATE' 'signal/warning plates' are installed on the DC-10 fleet; it made sense to install the red 'DO NOT OPERATE' 'signal/warning plates' to satisfy Step-7: 'Tag and mark each deactivation tool to indicate the tool must be removed prior to system activation.'  [Recommend to] standardize the procedure within the CF6 Thrust Reversers.  Installing the 'stow bolts' and the red 'DO NOT OPERATE' 'signal/warning plates' takes a couple of minutes to install.  Our other fleets currently use the procedure and the DC-10 has the identical thrust reversers and could be used as the validation for the procedure.  If standardization isn't the solution; a clarification or a rewrite would be another solution; like a note in the current MEL that the 'stow bolts' and red 'DO NOT OPERATE' 'signal/warning plates' are not to be used [on DC-10 CF6 Thrust Reversers].
A Line Aircraft Maintenance Technician (AMT) describes how human error and inconsistencies in MEL procedures contributed to a company DC-10 aircraft incurring damage to Number 3 Engine Thrust Reverser during Maintenance troubleshooting.