Come down on fire (6)
I believe the answer is:
alight
This clue is a double definition.
'come down' is the first definition.
(alighting is a kind of coming down)
'on fire' is the second definition.
('alight' can be a synonym of 'on fire')
(Other definitions for alight that I've seen before include "Disembark; on fire" , "Come down - on fire" , "Come to rest on the ground" , "Small restaurant" , "in flames" .)