The most common and most likely answer to this crossword clue is the 7 plus 7 letter word BEIJING AIRPORT
I've seen this crossword clue in The Guardian
B
E
I
J
I
N
G
A
I
R
P
O
R
T
Buddy explains!
The straight part
We know that "One of 4’s" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one of 4’s = beijing airport.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.