The most common and most likely answer to this crossword clue is the 9 letter word UNFLEDGED
I've seen this crossword clue in Financial Times
U
N
F
L
E
D
G
E
D
More clues leading to the result UNFLEDGED
Buddy explains!
The straight part
We know that "not able to fly yet" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not able to fly yet = unfledged.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.
What does UNFLEDGED mean?
UNFLEDGED adjective- Not having feathers; (of a bird) not yet having developed its wings and feathers and become able to fly.
- Not yet fully grown or developed; not yet mature.
- Inexperienced, like a tyro or novice.