Sky Pirates

From the introduction: The party becomes caravan guards for a fleet of airships carrying valuable, flammable cargo. ... The party learns of a high-paying job for guarding a caravan, but it turns out the caravan in question is a small fleet of airships transporting valuable, secret cargo. The job is high paying enough that several other groups have taken interest and the party needs to prove they're the best ones for the job. This may involve proving they're the best or convincing the other parties to let them have it.