B767-300 and 300 ER
Maintenance Airframe; Maintenance Powerplant
Communication Breakdown; Confusion; Situational Awareness; Troubleshooting
Aircraft Equipment Problem Critical
General Maintenance Action
Aircraft; Procedure; Manuals; Human Factors; Chart Or Publication
While performing other tasks; I noticed the 'Module Fault' fault ball tripped on a Rudder Ratio Changer Module (RRCM). Following the Fault Isolation Manual (FIM); a Step seems to be missing/not making sense; or possibly could use an additional decision block. Block-3 asks if fault ball is currently set after System Test (in this case; 'No'). Block-4 asks if fault ball was set prior to test; (in this case; 'Yes') and if 'Yes'; the FIM doesn't afford the ability to determine the system 'OK' via the previously performed test; but instead requires; regardless of subsequent decision; Block-56 (in this case; 'No'); further tests/troubleshooting even with no faults current on the [RRCM Module] box. This [RRCM] fault ball being set is fairly common on initial power-up of the B-767 fleet; (along with the 'STAB TRIM' EICAS message as well). Perhaps add a block to the Fault Isolation Tree to determine if the fault/fault ball has recurred in the last XX days/flights before mandating additional Checks/Tests? or a block; checking if the aircraft was just 'powered up'; and if so; the system is 'OK'.
Reporter stated the stab trim and rudder ratio changer are probably the most reliable systems on the B767 aircraft. Both modules however; have a common tendency to latch EICAS messages and set fault balls during initial power-up of the aircraft if hydraulics pumps are not running; due to the Stab Trim Control Module (STCM) and Rudder Ratio Changer Module (RRCM) sense low hydraulic pressure. He consistently uses the Fault Isolation Manual (FIM) for troubleshooting and wishes more Maintenance personnel would also. But his issue is with the procedure in the (FIM) for addressing EICAS Status Level Fault messages on the EICAS Maintenance Page that requires further tests and/or troubleshooting of the very faults he has already cleared. Reporter stated his Engineering Department agrees with him and has sent a suggested revision change request to Boeing for consideration after recognizing that unnecessary departure delays could have been avoided.
A Line Aircraft Maintenance Technician (AMT) suggests a revision that would add another Block Decision Step to Boeing's Fault Isolation Manual (FIM) for B767 aircraft. The revision would reduce the required additional tests for Rudder Ratio Changer Module faults that commonly appear after initial aircraft power-up.