Aint is classed as a negative auxiliary verb because it can occur sentence-initially to introduce a polar negative questions as in Example 178 Aint you know say comin back rebel time? This is not possible with na.
Source: Turner [1949] 2002: 260
Source: Turner [1949] 2002: 260
Source: Turner [1949] 2002: 264
Source: Turner [1949] 2002: 262
Source: Turner [1949] 2002: 262