Russian aircraft helping mass movement (9)

I believe the answer is:

migration

'mass movement' is the definition.
(I've seen this before)

'russian aircraft helping' is the wordplay.
'russian aircraft' becomes 'mig' (I've seen this before).
'helping' becomes 'ration' (I've seen this before).
'mig'+'ration'='MIGRATION'

(Other definitions for migration that I've seen before include "Periodic movement of groups of animals" , "Mass movement" , "Roaming it? (anagram)" , "Annual movement from one place to another" , "Periodic passage of animals from one place to another" .)

I've seen this clue in The Telegraph.

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