I need help remembering the title of a specific movie!!?

It's driving me nuts, i remember the movie but not the title. and i remember loving it as a kid, and i'd like to watch it again! It's animated, probably from the early 90's, and it's about a bunch of woodland creatures that have to run from some gas that has leaked into the forest. i think humans are the cause... and the gas is killing the animals. There is an old badger, and i think his granddaughter gets sick from the gas, so a group of young animals have to travel far away to retrieve some flower that will save the little badger's life. they use a flying machine that the old badger built.... does anyone know what movie i'm talking about???? i also remember they encounter some tractors and think they're some kind of foreign monster.