‘plus ça change, plus c'est la même chose’. In English, we say "The more things change, the more they stay the same". That's what it means.
"The more, the merrier"; "The more expensive the item, the more you have to pay", "The more you eat, the fatter you become."
The sentence means, "If a plane is heavier, then it will need more fuel." or "A heavier plane needs more fuel."
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