Shoot all of the engines off of a Zeppelin. It will stop dead in its tracks. You can also write words on them with gunfire. You can make the Zeppelin kill itself by finding one that shoots rockets and spraying it with gunfire. Then, fly underneath and wait until it shoots. Then, do a 90 degree turn upwards and watch it explode. When you get to the Lost City, fly by the tourist's Zeppelin and you can hear them cursing softly.