Inertial separator and method of use

A method of processing air flow into an operating engine, the method comprising:

• passing air into an inlet of an inertial separator comprising
• (a) an inlet tube having the inlet at an inlet end, an outlet at an opposite outlet end, the outlet end including an undercut, and a central passage between the inlet end and the outlet end;
• the outlet end including the undercut;
• (b) a deflector coaxially mounted in the central passage, the deflector having a plurality of spaced centrally joined helical vanes abutting the wall of the central passage;
• (c) a coaxially arranged outlet tube positioned within the outlet end of the inlet tube, the outlet tube having a first end and an opposite second end, the first end having an inlet, the second end having an outlet, and an outlet tube central passage between the inlet and the outlet in fluid communication with the central passage of the inlet tube, the outlet tube including first and second pairs of first and second anti-rotation tabs, wherein first and second anti-rotation tabs of the first pair of anti-rotation tabs are spaced further apart than first and second anti-rotation tabs of the second pair of anti-rotation tabs,
• the inlet of the outlet tube being of lesser diameter than the central passage of the inlet tube, the outlet tube having an outer surface having a spiral ramp having a first ramp end and a second ramp end, the spiral ramp having a portion angled downwardly toward the second ramp end and the undercut;
• and,
• (d) a scavenge flow outlet adjacent the undercut and the second ramp end;
• and,
• passing scavenge-depleted air from the outlet of the outlet tube into the operating engine, and passing scavenge flow from the inertial separator through the scavenge flow outlet.