Which Airline Has Most Delays? What the Data Shows

Which airline has most delays?

There is no single airline that permanently holds the title. The Bureau of Transportation Statistics (BTS) publishes on-time and delay data for U.S. carriers every month, and the carrier with the worst record shifts from one reporting period to the next. What BTS data does show consistently is why flights run late, and that breakdown is more useful for a traveler than chasing a moving target.

In BTS's national delay-cause figures for June 2026, the single biggest reported category was not weather and not even an airline's own operations directly. It was aircraft arriving late from an earlier flight, which triggered 9.94% of tracked operations that month.

What actually causes flight delays

BTS tracks reported U.S. flight delays in five categories. The table below shows the national percentages BTS reported for June 2026.

Delay category	June 2026 (national)	Plain-English meaning
Aircraft arriving late	9.94%	The plane due to operate the flight is still finishing a delayed earlier trip.
Air carrier delay	7.36%	Problems inside the airline's control, such as crew or maintenance issues.
National Aviation System (NAS) delay	6.42%	Broader system conditions: non-extreme weather, airport operations, and traffic volume.
Weather delay	1.03%	Extreme weather at the affected airport or along the route.
Security delay	0.04%	Checkpoint or security-related holds.

Two things stand out. First, late-arriving aircraft outranked every other category, including delays BTS classifies as directly airline-caused. A knock-on delay from an earlier leg is still frustrating for the passenger on the later flight, even though it did not start as that flight's own problem. Second, extreme weather was a comparatively small share of the national total that month — the popular assumption that storms drive most delays does not match BTS's own monthly breakdown for June 2026.

Airline-caused delays versus everything else

When people ask which airline has most delays, they usually mean one of two different questions: which airline's own operations cause the most trouble, or which airline's passengers experience the most delayed arrivals overall, regardless of cause. BTS's air carrier delay category is the closer match to the first question, since it isolates problems inside the airline's control, such as crew scheduling, aircraft cleaning, baggage handling, and maintenance. Late-arriving aircraft, NAS conditions, weather, and security are tracked separately because they are not purely an airline's own operating failure, even though the passenger still lands late.

This distinction matters when comparing carriers. An airline that runs a tight hub-and-spoke schedule can absorb more knock-on delays from late-arriving aircraft simply because one late inbound flight can push back several outbound departures. That is a scheduling exposure, not necessarily a sign of poor airline management, and it is a different signal than a high air-carrier-delay percentage caused by repeated maintenance or staffing issues.

How to check a specific airline's on-time record

BTS TranStats is the public tool behind these numbers, and it lets you query results for one airline instead of the whole system.

1. Open BTS TranStats Airline On-Time Statistics. Data are available from January 1995 through June 2026, reported in local time on a 24-hour clock.
2. Choose how you want to search. TranStats supports lookups by individual airline, origin airport, destination airport, or flight number.
3. Pull the departure and arrival detail. Results include scheduled versus actual times, delay length, cancellations, and diversions.
4. Compare more than one month. A single bad-weather week can distort a one-month snapshot, so check a few reporting periods for the route or carrier you care about.
5. Cross-check the cause mix. Put the airline's own numbers next to the national cause breakdown above to see whether its delays look more like scheduling knock-on effects, weather exposure, or airline-controlled issues.

Why the ranking keeps moving

On-time data reported to BTS in 2026 covers 17 U.S. air carriers that each have at least 0.5% of total domestic scheduled-service passenger revenue — the group of airlines large enough to be tracked consistently, not every operator flying in the country. BTS also cautions that arrival-delay figures shown in some of its lookup tools may not match figures published elsewhere, so a fair comparison means using the same tool, the same time period, and the same carrier definition for every airline you compare.

Airline schedules also change seasonally. A carrier that leans on a hub vulnerable to summer thunderstorms or winter snow can look worse in some months and average out over a full year. That is one reason a single ranking rarely stays put for long, and why checking the current month's data matters more than remembering last year's headline.

What air traffic control does and does not control

It helps to know who actually makes the call when a flight runs late. The FAA has stated plainly that air traffic control does not cancel flights — travelers are directed to contact their airline to find out why a specific flight was canceled or delayed. The FAA does manage traffic flow across the National Airspace System, which handles an average of 44,360 flights a day, and system-wide congestion or a ground-delay program can still be the underlying reason a flight is held. But the decision to cancel, rebook, or hold a specific flight sits with the airline operating it, not with air traffic control.

That split matters when your own flight is delayed: the airline can tell you the cause and your rebooking options; FAA status pages can tell you whether the wider airspace system is congested that day. For what to do next, see why your flight is delayed and what to do during cancellations and delays.

Using this before you book

A monthly cause breakdown will not predict your specific flight, but it can inform how you choose between two similar itineraries. A nonstop avoids the extra failure point a connection adds. A flight scheduled early in the day has fewer opportunities to inherit a late-arriving aircraft from earlier rotations, since delays tend to compound as a travel day goes on. If you want the current single-airline leaderboard rather than the cause breakdown covered here, DOT's monthly ranking of individual carriers is the more direct answer — see how DOT ranks carriers each month and the latest single-airline result.

Delay data, carrier rankings, and FAA traffic conditions change constantly. Confirm the current month's numbers on BTS TranStats and check your operating airline's status page before you travel, rather than relying on an old ranking. If a delay does happen, see what happens if a delay causes a missed connection for the next steps.