The most common and most likely answer to this crossword clue is the 14 letter word ALLÂ SYSTEMSÂ GO
I've seen this crossword clue in The Guardian
A
L
L
Â
S
Y
S
T
E
M
S
Â
G
O
Buddy explains!

The straight part
We know that "Everything ready" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case everything ready = all systems go.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.