Side quest 3 · comparison · Jul 2026

Three hubs: who is actually on time?

Istanbul, Heathrow and Frankfurt — measured over the same 86-day window, from the same source, with the same delay definition. Departures only, cargo and cancellations excluded. The result was not what I expected.

Istanbul is the most punctual of the three. 11.7% of IST departures leave 15+ min late, against 16.6% at Heathrow and 19.1% at Frankfurt. A flight is 1.6x more likely to depart late from Frankfurt than from Istanbul. This isn't one bad week skewing an average — the 7-day rolling chart below holds the same ordering for three straight months.

How delay builds through the day (local time)

Share of departures leaving 15+ min late, by each airport's own local hour. Hover the lines to compare all three at once.

This is where the real difference is. Frankfurt climbs from 3.4% in the early morning to 27.9% by midday — the day's delay accumulates and never drops below 21% again until late evening. Heathrow does the same, peaking at 26.3% at 18:00. Istanbul stays flat at 5–16% all day: it doesn't carry morning lateness into the evening. That matters as much as the headline rate — IST absorbs the day instead of compounding it.

Why are the LHR and FRA lines shorter? Both operate under night flight restrictions, so there aren't enough late-night departures to compare (the chart requires at least 150 flights in an hour to plot it). Istanbul runs 24 hours. IST's single spike at 05:00 rests on thin data — don't read anything into it.

Is the gap persistent, or just a bad week?

7-day rolling average, 3 May – 27 July 2026. The ordering never changes across the whole three months.

When it is late, how bad is it?

The full bar is the share of all departures running late; the segments split that by how late. Darker means longer.

Frankfurt is often late but briefly; Heathrow is late less often but harder. 10.3% of FRA departures slip 15–30 min — the highest of the three — yet its share of delays over an hour (2.4%) is nearly identical to Istanbul's (2.2%). Heathrow delays less often but pays more when it does: 3.4% run over an hour, half again as many as IST.

The numbers

The data behind the charts. "Departures in sample / day" is how many flights this dataset captured per day — not the airport's true total traffic.

Method and limits

Delay = aviationstack's gate departure delay; the "late" threshold is 15+ min. Departures only; cargo flights and cancellations excluded. All three airports cover the same window (3 May – 27 July 2026) and run through the same code; partially-collected days were dropped, leaving 83 days for IST and 82 for the other two. This is a snapshot, not live. IST is still collected daily; LHR and FRA were a one-off historical pull.