The aircraft's day
Where was a late flight's delay born?
Every flown leg with a tail number was put back in order on its aircraft's day. Pick a day, or take the worst day of a month, and an aircraft: the timeline shows each leg's arrival delay and how much of its departure delay it inherited from the leg before, using the propagation coefficient of 1.068 and the minimum turn of 45 min estimated in chapter 4.
The aircraft's day, leg by leg
Pick a day and an aircraft
Source: BTS Reporting Carrier On-Time Performance (real); rotations rebuilt from tail numbers in the warehouse's int_legs.
The buffer curve
About a third of arrival delay was inherited from the aircraft's previous flight, and a scheduled turn of 75 minutes halves what is passed on
Departure delay minutes passed on per minute of late inbound arrival, by scheduled turnaround
Minutes passed on per late minute
Source: BTS Reporting Carrier On-Time Performance, model: the propagation model, scheduled flights 2023 to 2026-07, as of 2026-10-01.
The integrity rules and what they did
A leg is linked to the one before it only when it leaves from the airport that one landed at, after it landed, within 6 h; a longer sit starts a new rotation. Of 72,583,211 legs, 54,431,369 were linked (75.0%), 10,019 were the first leg on their tail, 17,170,752 followed a gap, 369,126 broke the chain and were split rather than joined (most are aircraft swaps the tail number does not show), and 601,945 were impossible sequences, quarantined and counted. That leaves 18,151,842 rotations on 10,019 aircraft.
What the ops director would push back on
Tail numbers miss aircraft swaps, so some links join two aircraft. The chain rules split a pair whenever the next leg does not leave from where the last one landed, which is what most swaps look like; a swap between two aircraft at the same airport inside one turn is invisible to any reconstruction from public data. The worst day of each month is chosen by the inherited minutes per linked leg, so the page shows the days propagation mattered most, not typical days.