Flight delay propagation or “ripple” is a well-known phenomenon in the National Airspace System (NAS). It is when delay on one flight leg carries forward to a future flight leg for the same aircraft due to the practice of airlines scheduling multiple flight legs per aircraft. The research investigates where delay propagation is occurring in the NAS by analyzing historical data. A backtracking algorithm is proposed to tally delay that is experienced on the ground and in the air for each flight leg, which later becomes observable schedule delay at downstream airports. Results are shown across different time periods, carriers, weather conditions, and airports.