air means "on" when used as a preposition, but it's also a prepositional pronoun, meaning "on him"/ "on it" - so, as here, the "he" is included in air.
The full list of prepositional pronouns with air is:
orm [air + mi] = on me
ort [air + thu] = on you (sing. inf.)
air [air + e] = on him/ on it
oirre [air + i] = on her / on it
oirnn [air + sinn] = on us
oirbh [air + sibh] = on you (pl. + sing. formal)
orra [air + iad} = on them
As a warning oirre and orra are very difficult/impossible to distinguish in speech!