Abdelmalik Petitjean, 19, “easily” passed security checks to work at Chambery airport near his home in Aix-les-Bains in the French Alps.
He worked there from December to April after getting his high school baccalaureate.
Chambery Airport handles 250,000 passengers a year, many of them Britons heading for the ski slopes.
His job gave him access to the luggage of thousands of travellers.
But in the spring Petitjean quit his job and in June was caught by Turkish intelligence trying to join IS in Syria.
Earlier this week he and fellow IS fanatic Adel Kermiche, also 19, stormed into a church near Rouen and slit the throat of 86-year-old priest Father Jacques Hamel before being gunned down by police.
It is the latest security lapse to hit France which is reeling from a spate of IS terror attacks.
Both fanatics were known to the security services and Kermiche had been released early from jail after twice trying to join IS in Syria.
He was electronically tagged and supposed to be living under curfew with his parents.