Big city training more pilots (10)
I believe the answer is:
metropolis
'big city' is the definition.
(I've seen this before)
'training more pilots' is the wordplay.
'training' is an anagram indicator (to train can mean to grow something into a shape).
'more'+'pilots'='morepilots'
'morepilots' is an anagram of 'METROPOLIS'.
(Other definitions for metropolis that I've seen before include "population centre" , "early film" , "London, say" , "Expressionist movie" , "centre of activity" .)