The most common and most likely answer to this crossword clue is the 7 plus 2 plus 3 plus 3 letter word CASTLES IN THE AIR
I've seen this crossword clue in Independent
C
A
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More clues leading to the result CASTLES IN THE AIR
- Flying Fortresses just daydreams?
- Unrealistic hopes of seeing rooks flying?
- Keeps up unrealistic plans
- Intricate hassle having to alter unrealistic plans
- Former minister inherits a messy set of unrealistic plans
- One can get lost in these non-realistic fantasies essentially getting built
- Hates recitals arranged to include popular imaginative items
Buddy explains!

The straight part
We know that "Flying Fortresses/just daydreams?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case flying fortresses/just daydreams? = castles in the air.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.