Believe it or not there are actually rules for air warfare. I don’t see anyone adhering to it when they are carpet bombing, blowing up schools and hospitals and killing innocent civilians. But there are rules they all try to stick too.
Air warfare, must comply with laws and customs of war, including international humanitarian law by protecting the victims of the conflict and refraining from attacks on protected persons.
These restraints on aerial warfare are covered by the general laws of war, because unlike war on land and at sea—which are specifically covered by rules such as the Hague Regulations and Protocol I additional to the Geneva Conventions, which contain pertinent restrictions, prohibitions and guidelines—there are no treaties specific to aerial warfare.
To be legal aerial operations must comply with the principles of humanitarian law: military necessity, distinction, and proportionality:
An attack or action must be intended to help in the military defeat of the enemy, it must be an attack on a military objective, and the harm caused to civilians or civilian property must be proportional and not excessive in relation to the concrete and direct military advantage anticipated.