Castaway from ship's company dead, so the radio said (6)
I believe the answer is:
crusoe
'castaway' is the definition.
(Robinson Crusoe, from the novel by Daniel Defoe)
'ship's company dead so the radio said' is the wordplay.
I cannot really see how this works, but
'so' is within the answer.
This explanation may well be incorrect...
'from' acts as a link.
(Other definitions for crusoe that I've seen before include "5 down [CASTAWAY]" , "Shipwrecked hero" , "Robinson . . . . . . was a famous fictional castaway" , "One stranded" , "See 9" .)