Synonyms to air piracy

letters of marque, Pastoral Epistle, aerogram, air letter, airgraph, airplane hijacking, billet-doux, buccaneering, bull, chain letter, dead letter, dimissorial, dimissory letter, drop letter, encyclical, fan letter, form letter, freebooting, letter of credit, letter of introduction, letters credential, letters of request, letters overt, letters patent, letters rogatory, love letter, monitory, newsletter, nixie, open letter, pastoral letter, piracy, poison-pen letter, privateering, round robin, skyjacking