B757-200
Maintenance Airframe; Maintenance Powerplant
Communication Breakdown; Confusion; Situational Awareness
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
MEL; Human Factors; Aircraft; Procedure
While reviewing the B757 MEL; I read [Chapter] 49-Xs [language add-on] for APU Pneumatic issues and I then went to MEL 36-12; APU Shutoff Valve; and was trying to distinguish the difference between the two MELs. They refer you to the same diagram; and [I] wanted to know exactly what APU Pneumatic function meant. The second issue is that [MEL Chapter] 36-12; Paragraph-A; Subsection-1; refers you to the APU Shutoff Air switch; of which does not exist on a B757. An APU Bleed Air switch; does however reside in the cockpit. Please clarify; as I would hate to use the wrong MEL for placarding an APU Pneumatic System. On that note; which MEL would be proper to use when placarding the APU Air?
A Line Mechanic requests clarification of add-on language to their MEL Chapter-49 APU pneumatic issues for B757 aircraft; in order to understand the difference between that chapter and MEL Chapter 36-12 APU Shutoff Valve. Concerns about applying an improper MEL for an APU Pneumatic System deferral were also noted.