28 parses as 1-3 (a term for FBI agents - coincidentally it appears in today’s ‘Speedy’) inside 3 letters for group.
16d def is the first four words. 3 letters reversed for airline’s, then an anagram.
17d. an anagram.
21. 6 letter author missing first two letters. Def is sack
27. One letter from ‘ultimately the’’ and 3 letters for tin all inside 4 letter word for herb (I didn’t know this). Def is VIPs team.
Hope that helps