When vowel A is in an unaccented syllable, it can change to a schwa sound. 

When vowel A is in an open syllable at the end of a word, most of the time it becomes a schwa, as in “hula”.

/ə/, /ə/, /ə/, hula

When vowel A is in an unaccented syllable, closed or glued, it can also become a schwa, as in “human”

/ə/, /ə/, /ə/, human