The most common and most likely answer to this crossword clue is the 11 letter word OPERATIONAL
O
P
E
R
A
T
I
O
N
A
L
More clues leading to the result OPERATIONAL
- Frank, mostly sensible, is running
- Working out initially sensible following PE
- Working to create a large base for theatre event
- Working off energy on allotment, breaking up stone
- Working not compulsory, having a lot of time?
- Functional Old English sound involves piano
- Working time’s voluntary outside
- Working is a matter of choice — about time!
- Running musical piece’s characterised by notes, I gathered
Buddy explains!

The straight part
We know that "Running" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case running = operational.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 OPERATIONAL mean?
OPERATIONAL adjective- Of or relating to operations, especially military operations.
- Functioning and ready for use.
- Effective or operative.
- Determined by means of practical measures.