The most common and most likely answer to this crossword clue is the 8 letter word AUTOGYRO
I've seen this crossword clue in The Daily Telegraph
A
U
T
O
G
Y
R
O
More clues leading to the result AUTOGYRO
Buddy explains!
The straight part
We know that "Heavier than air machine" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case heavier than air machine = autogyro.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 AUTOGYRO mean?
AUTOGYRO noun- An aircraft in which lift is provided by unpowered rotating wings and thrust is provided by a conventional propeller.