This document covers the recommended procedure for replacing the carbon brushes incorporated within an Airmaster sensor-brush assembly (A0120 or A0122).
The brushes that run on the slipring will progressively wear down during service. Once they have become so worn that the springs behind them are at full extension, the brushes will no longer provide sufficient contact with the slipring. This may be observed during an inspection of the propeller or may become apparent as an open circuit alarm (as indicated by all three lamps flashing red on the controller).
Carbon Brush Replacement R1a 
