DC-10 Undifferentiated or Other Model
Maintenance Airframe; Maintenance Avionics; Maintenance Powerplant
Maintenance Avionics 15; Maintenance Technician 10
Communication Breakdown; Confusion; Situational Awareness; Training / Qualification
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Procedure; Manuals; Human Factors
NOTE: This Maintenance report applies to all company DC-10 Aircraft; not just Aircraft X. The Pressure Regulating Shutoff Valve (PRSOV) and Overpressure Shutoff Valve (OPSOV) connections to all TRAS Lock Engine Duel Switcher valves are not connected properly. It has been verified via company Engineering that the PRSOV valve is actually connected to the Dual Switcher Valve OPSOV connection and the OPSOV valve is actually connected to the Dual Switcher Valve PRSOV connection. The connections are backwards. This is causing some Thrust Reversers to stow during Auto Re-Stow Testing in Maintenance. If the lines were properly connected; the Thrust Reverser would not be able to stow during testing. Flight Safety - It has always been my understanding that the OPSOV is solenoid controlled air to the Dual Switcher Valve. A company Engineer recently pointed out that engine air is actually at the Dual Switcher Valve anytime the engine is running. He showed me the [McDonnell-Douglas] LAMM schematic which shows the air flow to the Dual Switcher Valve with no solenoid control. The PRSOV valve could be open in flight as it is on the ground during the Auto Re-Stow test as a result of the lines being connected backwards. [Recommend] to properly connect the lines to the Dual Switcher Valve. Verify if the OPSOV air is still solenoid controlled air. If not; then we must connect the lines to the Dual Switcher Vavle properly. If the OPSOV is solenoid operated; then inform Engineering and change the LAMM [schematic] to reflect this.
Reporter stated he has been working avionics and thrust reversers for over twenty-five years. The Thrust Reverser Actuation System (TRAS) and mechanical Locks are part of an FAA A.D. that also requires installation and testing of a Dual Switcher Valve component on each GE CF6-80 series engines with connections for the Pressure Regulating Shutoff Valve (PRSOV) and Overpressure Shutoff Valve (OPSOV) rigid pneumatic lines. The whole intent of the AD is to reduce the potential for reverser deployment in flight. Three requirements must be met to allow the PSROV air to be available for reverser movement. Reporter stated he believes the engine pneumatic lines to the Dual Switcher Valve were misrouted during the initial Switcher valve installation approximately several years ago. The pneumatic flow line from the OPSOV that should go to the OPSOV on the Dual Switcher Valve actually goes to the PSROV connection on the Switcher Valve which should have air flowing out; not into the Switcher Valve. As a result; the pneumatic air line that should have been connected to the Switcher Valve for 'air flow to' the PRSOV was connected to the OPSOV port on the  Switcher Valve. Pneumatic air pressure was/ is on the wrong side of the Switcher Valve. The Dual Switcher Valves have four lines. Three lines are input and one line for output.  The Boeing LAMM schematic also shows air pressure at all times; but that is not correct; because there is a solenoid that actually interfaces and does not allow the PSROV to open unless the same three conditions are satisfied. Reporter stated he would like to see two issues addressed. 1) switch the pneumatic lines at the Dual Switcher Valve to operate correctly. 2) Revise the Boeing LAMM schematic for the two pneumatic line connections to the Switcher Valve to prevent continued incorrect stowing of reversers during Auto-Re-Stow Testing of the Switcher Valve and reversers.
An Aircraft Maintenance Technician (AMT) with extensive DC-10 Engine Reverser experience describes what he believes to be inaccurate Boeing Lamm schematics that have contributed to engine pneumatic lines being attached at incorrect positions on Dual Switcher Valves on GE-CF6-80 engines. The Switcher Valves are part of the FAAs Thrust Reverser Safety Enhancement System A.D.