Surviving crew no longer appearing to be getting on (5)
I believe the answer is:
aging
'be getting on' is the definition.
(get on can mean to get older)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for aging that I've seen before include "Getting older" , "in decline" , "Growing older" , "development" , "Becoming more grown-up" .)