The most common and most likely answer to this crossword clue is the 11 letter word AIRCRAFTMAN
I've seen this crossword clue in The Times
A
I
R
C
R
A
F
T
M
A
N
Buddy explains!
The straight part
We know that "Member of service personnel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case member of service personnel = aircraftman.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 AIRCRAFTMAN mean?
AIRCRAFTMAN noun- A member of the lowest rank in the Royal Air Force or the air forces of various other Commonwealth countries.