The most common and most likely answer to this crossword clue is the 8 plus 4 letter word BOARDING PASS
I've seen this crossword clue in The Sunday Telegraph
B
O
A
R
D
I
N
G
P
A
S
S
More clues leading to the result BOARDING PASS
- Examination body in good successful result means to get on
- Needed to fly when staying with Dad and sisters on vacation
- Swine, big noise, doctor and idiot get authorisation to fly
- Living-in pupil’s exam success – needed for high-fliers
- For getting on plane: directors get in first, then doctor, then an American behind
- Sad OAP brings invalid travel document
- Requirement for a jet-setter to get on?
- British and Spaniards go astray — it’s necessary to take flight
- Possibly drop in bags as requirement if you’re flying
- In residence at college, I don’t know what’s needed to get through the gate
Buddy explains!
The straight part
We know that "it’s necessary to take flight" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s necessary to take flight = boarding pass.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.