1 across: they're used when surveying aircraft schedules (5-6) flight something?
11 across: Get in a tangle with a composer (5)
16 across: A saving grace ? (6)
7 down: suitable to take possession of (11)
3 down:Book Five in Christmas setting (5) Beginning with G I think!
12 down: Invite P.O.W to give an opinion (9)
Novel is correct, thanks.
17 across: One of the ways in which urban life can be seen (6)
:15 across"Elementally disturbed, in the main (5-6)
11 The captain is one who can handle a rope (7)