The initial idioms of the letter A

be on the bum	be on the cards
be on the case	be on the crest of a wave
be on the edge of (something)	be on the fritz
be on the front foot	be on the gravy train
be on the hook	be on the horn
be on the horns of a dilemma	be on the hush
be on the march	be on the mend
be on the ragged edge	be on the right lines
be on the right track	be on the rocks
be on the ropes	be on the run
be on the same wavelength	be on the sick list
be on the side of the angels	be on the skids
be on the square	be on the table
be on the threshold of (something)	be on the warpath
be on the wing	be on the wrong end of (something)