The most common and most likely answer to this crossword clue is the 11 letter word JETTISONING
I've seen this crossword clue in The Times
J
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More clues leading to the result JETTISONING
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The straight part
We know that "dumping fuel, say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dumping fuel, say = jettisoning.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 JETTISONING mean?
JETTISONING verb- To eject from a boat, submarine, aircraft, spaceship or hot-air balloon, so as to lighten the load.
- To let go or get rid of as being useless or defective.