There is nothing wrong with working on maintenance of the airplanes that transport passengers, and this work is not rendered haraam by the haraam foods and drinks that may be served on board, because the work itself is permissible, which is transporting passengers from one place to another. And this is something that comes under the heading of necessity for many people.
The airline company and the passengers should also refrain from what Allah has forbidden.
Maintenance only becomes haraam work if it is helping a sinner to commit sin, such as working on maintenance of military aircraft for a state that is at war with the Muslims… and the like.
And Allah knows best.