The most common and most likely answer to this crossword clue is the 4 plus 7 letter word TREE SURGERY
I've seen this crossword clue in The Times
T
R
E
E
S
U
R
G
E
R
Y
Buddy explains!
The straight part
We know that "working on a plane, perhaps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case working on a plane, perhaps = tree surgery.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.