The most common and most likely answer to this crossword clue is the 6 plus 5 letter word FLYING START
I've seen this crossword clue in The Times
F
L
Y
I
N
G
S
T
A
R
T
More clues leading to the result FLYING START
- Initial advantage / Wrights gave us?
- Initial success as gnat, firstly, squished
- Wonderful first part, second parts pie in the sky?
- Fraudulent celebrity in paper getting initial advantage
- Getting both feet off the ground in initial movement?
- Get to taxi before this promising beginning?
- Beginning of aerial race?
Buddy explains!

The straight part
We know that "Initial success" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case initial success = flying start.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.