The most common and most likely answer to this crossword clue is the 4 plus 2 plus 8 letter word BIRD OF PARADISE
I've seen this crossword clue in The Daily Telegraph
B
I
R
D
O
F
P
A
R
A
D
I
S
E
More clues leading to the result BIRD OF PARADISE
Buddy explains!
The straight part
We know that "flier" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case flier = bird of paradise.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.