B767-300 and 300 ER
Maintenance Airframe; Maintenance Powerplant
Maintenance Inspector 5; Maintenance Lead Technician 5; Maintenance Technician 29
Training / Qualification; Situational Awareness; Fatigue; Confusion; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Maintenance
General Maintenance Action
Aircraft; Human Factors; MEL; Procedure
After successfully deferring Left Engine Thrust Reverser; crew reported Left Engine Thermal Anti-Ice EICAS Status message. I reported problem to my maintenance supervisor and he assigned 3 other mechanics to help me with the deferral. Maintenance Control decided the best course of action was to defer the left thermal anti-ice valve to MEL in the open position. The MEL has you comply with 2 additional MELs; 1 Cat downgrade and several procedures to be complied with.After deactivating the nose cowl thermal ant-ice valve in the open position the MEL has you open both Engine fan cowls and thrust reverser halves and lock the HPSOV (High Pressure Shut-Off Valve) in the closed position per maintenance procedure. The procedure only references a picture of the valve. By mistake we locked the PRV (Pressure Reducing Valve) in the closed position by accident. This valve is located just above the HPSOV. The aircraft departed. When the aircraft landed the pilot reported they had no Left Engine Bleed air.One thing I would also comment on is our MEL does not have any page numbers making it confusing and easy to make a mistake when you have such an involved deferral with multiple maintenance procedures and bounces you all around the manual making it easy to miss something. This is something that bothers most AMTs. With the pressure of making service; the confusion of the MEL; 4 mechanics working on the same job and fatigue all added to the problem.
Maintenance Technician reported when they deferred a nose cowl anti-ice valve on a B767 they mistakenly locked-out the incorrect valve.