The most common and most likely answer to this crossword clue is the 7 letter word CATBIRD
I've seen this crossword clue in Independent
C
A
T
B
I
R
D
More clues leading to the result CATBIRD
Buddy explains!

The straight part
We know that "US flier" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case us flier = catbird.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.
What does CATBIRD mean?
CATBIRD noun- Either of two species of American mockingbird relatives, the grey catbird, Dumetella carolinensis, and the black catbird, Melanoptila glabrirostris.
- Any of four species of Australasian bowerbirds of the genera Ailuroedus and Scenopoeetes.
- A babbler-like bird from eastern Africa, Parophasma galinieri.