Yes, you use an airlock as long as it is in a fermenter--primary, secondary or tertiary.
"Cast your bread upon the waters for after many days you will find it again. Give portions to seven, yes to eight, for you do not know what disaster may come upon the land." Ecclesiastes 11:1f
Who knew there was an ancient recipe for beer in the Bible?
My paraphrase: "Since you don't know what disasters might befall you , when you make beer share it with friends. Someday you might need them to share with you."