Full grid apart from from the 16 empty cells, 8 of which i have filled( unclued down entries) from the missing wordplay letters. Unsure what's next ...the string, final resting place ,move ??
The 'string' is the everyday name for the 37(I think, I'm out so can't check my copy) entry. It appears in the grid, from near the top left and makes it way along.
Close the trap (this will leave 4 empty cells on either side of the open position). You should then have a 2x4 central rectangle - the final resting place for two things that flew).
You've got the 2 (ex)fliers from the V... and the A... extra letters from clues, and if you've put them in the right order you'll have real words throughout (ignoring gaps).