What is the most common cause of flight delays?

In the United States, a late-arriving aircraft is the largest single cause. Across 2025, about 39% of the delay minutes that US reporting airlines assigned to a cause came from the previous flight on the same plane arriving late. Air carrier delays, those within the airline's control, came second at about 32%, ahead of National Aviation System delays at about 22%.

How can I tell early that my flight will be late?

Look at the aircraft that will operate your flight. If the plane is still arriving from somewhere else and that inbound flight is late, yours usually leaves late too. Check the airline app for the inbound flight's status and the FAA's NAS Status page for a ground stop or ground delay program at your origin or destination airport.

What is a ground stop?

A ground stop is an FAA traffic management action that holds flights bound for an affected airport at their departure points while it lasts. The FAA's NAS Status guide says it can be used to control traffic volume, to allow time to set up a ground delay program, or when an airport cannot accept any arrivals. It shows on the public NAS Status page.

When does a US airline owe me a refund for a delay?

As of October 2026, under 14 CFR 260.6 a covered carrier that is the merchant of record must refund a nonrefundable ticket on a flight to, from or within the US if the flight is cancelled or significantly delayed and you decline the changed flight, rebooking and any voucher. Significant means 3 hours or more domestic, 6 hours or more international.

Does the airline have to pay me compensation for a delay?

Part 260 is a refund rule: it returns your fare, taxes and ancillary fees, in the original form of payment, with no processing fee. It is a return of what you paid, not an extra payment. For meals, hotels or rebooking on another airline, ask the airline what it will offer for your flight.

Should I cancel a delayed flight right away?

Usually not. Under Part 260 your refund right attaches to a significant delay or change to the itinerary, and a flight that is late but still within the threshold gives you no refund claim. Watch the status, ask what the airline will offer, and only decline the flight once the new schedule clearly crosses the threshold or no longer works for you.

Does Flydar warn me about delays?

No. Flydar watches fares on routes you set and emails you when one drops clearly below what that route normally costs. It does not track flight status, warn about delays or rebook you. For day-of-travel status, use your airline's app, the airport's departures board and a flight tracker.

Why flights get delayed, and when a delay is yours to cancel

Most US flight delays start with the aircraft, and weather is a smaller share than people expect. In 2025 the largest share of delay minutes, about 39%, traced to the previous flight on the same plane arriving late. Airline-controlled problems came next at about 32%. A US airline owes you a refund for a nonrefundable ticket only once the delay is “significant”: 3 hours or more domestic, 6 hours or more international.

At a glance

Largest US cause, 2025: late-arriving aircraft, about 39% of cause-assigned delay minutes (BTS data, January to December 2025).
Second: air carrier delay, about 32%. National Aviation System (NAS) delay about 22%, extreme weather about 6%, security about 0.1%.
Europe, 2025: air traffic control capacity was the main attributed reason for en-route delay (42.1%), ahead of adverse weather (28.5%) and ATC staffing (15.9%), per Eurocontrol.
Early warning: the inbound aircraft’s status, plus ground stops and ground delay programs on the FAA’s NAS Status page.
Refund threshold (14 CFR 260.2, as of October 2026): 3 hours or more domestic, 6 hours or more international, for flights to, from or within the US.
A delay alone does not trigger a refund. You also have to decline the changed flight, rebooking and any voucher offered.

What causes most flight delays in the United States?

The US Bureau of Transportation Statistics (BTS) sorts every late arrival into five cause categories, and the biggest one is the previous flight on the same aircraft. BTS defines late-arriving aircraft as a case where a previous flight with the same aircraft arrived late, which caused the present flight to depart late.

The table below is our own tabulation of BTS’s public monthly on-time performance files for January to December 2025, which BTS also summarises on its delay causes page: 7.0 million scheduled flights by the large US reporting carriers, of which about 22% of flown flights arrived 15 or more minutes late. The shares are of the delay minutes assigned to each cause on those late flights.

BTS cause category	What it covers	Share of 2025 delay minutes
Late-arriving aircraft	Previous flight on the same plane was late	39.2%
Air carrier	Within the airline’s control	32.5%
National Aviation System	Delays within the national air system, outside the airline’s control	21.9%
Extreme weather	Extreme weather only	6.4%
Security	Security-related delays	0.1%

Two points stop the table misleading you. First, “late-arriving aircraft” is a knock-on category. BTS notes airlines do not report why the earlier flight was late, so a share of it started with an airline problem, weather or air traffic delay earlier in the day. Second, BTS’s weather category covers extreme weather only. Weather that slows operations without stopping flights is counted under the National Aviation System, so weather’s real share is larger than 6%.

Monthly numbers move more than annual ones, so treat these shares as a pattern for planning, not a forecast for your flight.

Why are flights delayed in Europe?

Eurocontrol’s 2025 Performance Review Report attributes most of Europe’s en-route air traffic delay to air traffic control capacity. Of en-route ATFM (air traffic flow management) delay in 2025, ATC capacity was 42.1%, adverse weather 28.5%, ATC staffing 15.9%, ATC disruptions 5.0%, other causes 4.5% and projects 4.1%.

Average en-route delay fell from 2.13 minutes per flight in 2024 to 1.67 minutes in 2025, and Eurocontrol still describes network performance as far below expectation. At the 30 busiest European airports, the average pre-departure delay was 14.7 minutes per departure in 2025, and the report says airline delays remain the largest contributor across the year, with en-route delay driving the summer peak.

Knock-on effects matter in Europe too: in 2025 one minute of primary delay generated 0.79 minutes of reactionary delay on later flights, down from 0.82 in 2024. The US and European figures use different methods and thresholds, so do not compare the percentages directly. The shared lesson is that a late start early in the day tends to spread.

How can you tell early that your flight will be late?

Check the aircraft that will operate your flight, then check the airports on either end. The aircraft is the cause behind roughly two in five US delay minutes, and its status is visible before the airline updates your departure time.

Find the inbound flight. Your plane is arriving from somewhere. If that earlier flight is running late, your flight probably will too. Your airline’s app often shows the status, and FlightAware has added a “Track inbound flight” option for dozens of airlines.
Check the FAA’s NAS Status page. The FAA’s user guide describes it as a public application showing current and forecast traffic management initiatives, including airport delays, closures and airspace delays. It lists ground stops, ground delay programs, arrival and departure delays and deicing.
Know what a ground stop and a ground delay program mean. In a ground stop, flights bound for the affected airport are held at their departure point. In a ground delay program, traffic bound for the airport is delayed at departure until each flight’s expected departure clearance time, used when projected demand is expected to exceed the airport’s acceptance rate for a lengthy period.
Ask the airline for the reason. FlightAware says it does not receive operational details on the specific causes of delays or cancellations, and recommends contacting the airline.

When does a US airline owe you a refund for a delay?

As of October 2026, 14 CFR 260.6 requires a covered carrier that is the merchant of record to give a full and prompt refund of the airfare, including taxes and ancillary fees, on a nonrefundable ticket for a scheduled flight to, from or within the US. The flight must be cancelled or significantly delayed or changed, and you must decline the alternative, whether that is rebooking, a voucher or other compensation offered.

“Significantly delayed or changed” is defined in 14 CFR 260.2. It includes a departure or arrival moved by 3 hours or more on a domestic itinerary, or 6 hours or more on an international one. It also includes a different origin or destination airport, a downgrade in class of service, or an itinerary with more connection points.

Situation	Refund right under Part 260
Domestic flight rescheduled by 3 hours or more	Yes, if you decline the changed flight, rebooking and any voucher
International flight rescheduled by 6 hours or more	Yes, on the same condition
Delay of 90 minutes, flight still goes	No refund claim under Part 260
Flight cancelled, no alternative offered	Automatic full refund
You accept the new flight or the voucher	No refund; you took the alternative

Four details to keep in hand:

How the money comes back. Under 14 CFR 260.10, the refund goes back in the original form of payment unless you agree to a cash equivalent, and the carrier may not keep a processing fee. 14 CFR 260.2 defines “prompt” as within 7 business days for credit card purchases and 20 calendar days for cash, check, debit card or other forms.
Notice. 14 CFR 260.9 requires the carrier to timely notify affected consumers about a cancellation or significant delay or change.
Who pays. The obligation sits with the carrier that is the merchant of record. If you booked through a travel agency, the refund route may differ, so read the booking confirmation first.
Refund only. Part 260 returns what you paid. For meals, hotels or rebooking on another airline, ask your airline what it will offer for your flight.

When should you change your plans because of a delay?

Hold your ticket until the airline’s new schedule crosses a line that matters to you, then act fast. Cancelling early gives up the options a rebooking would have given you, and your refund right under Part 260 depends on the rescheduled times, not on how the delay feels.

Watch first. If the delay is under an hour and your connection has slack, wait and keep checking the status.
Ask what the airline will do. Ask whether it will rebook you on a later flight, or on another airline, at no extra cost.
Do the arithmetic on your connection. Whether a late first flight is covered depends on whether the legs are on one ticket or on separate tickets. What happens if you miss your flight and self-transfer flights cover those two cases.
Only then decline. If the new schedule crosses 3 or 6 hours, or no longer works for your trip, decline the changed flight and the voucher and ask for the refund. Taking the voucher or the new flight ends the refund right.

Rebooking is where a delay turns into a fare decision. A nonrefundable ticket you cancel for a refund puts you back in the market at short notice, which is the situation the one-way vs round-trip trade-off was built for. Flydar does not track flight status or warn about delays, but it does watch fares: set the route before your next trip and you will know what that route normally costs when a replacement ticket is needed.

Which step on that list would have saved you the last time a gate agent got to a long line first?

Sources

US Bureau of Transportation Statistics, TranStats Airline On-Time Performance data files, January to December 2025: https://www.transtats.bts.gov/ONTIME/Index.aspx (tabulated by us; checked October 2026)
BTS, Airline On-Time Statistics and Delay Causes: https://www.transtats.bts.gov/OT_Delay/OT_DelayCause1.asp (checked October 2026)
BTS, Understanding the Reporting of Causes of Flight Delays and Cancellations: https://www.bts.gov/topics/airlines-and-airports/understanding-reporting-causes-flight-delays-and-cancellations (checked October 2026)
Eurocontrol, Performance Review Report 2025: https://www.eurocontrol.int/sites/default/files/2026-03/eurocontrol-performance-review-report-2025.pdf (checked October 2026)
FAA, NAS Status: https://nasstatus.faa.gov/ and the NAS Status User Guide: https://nasstatus-alpha.faa.gov/static/media/NASStatusUserGuide.cccc6d48.pdf (checked October 2026)
eCFR, 14 CFR Part 260 (sections 260.2, 260.6, 260.9, 260.10), text current to 26 October 2026: https://www.ecfr.gov/current/title-14/chapter-II/subchapter-A/part-260 (checked October 2026)
FlightAware, Why was my flight delayed or cancelled?: https://support.flightaware.com/hc/en-us/articles/27638269763351-Why-was-my-flight-delayed-or-cancelled (checked October 2026)
FlightAware, Releases Major Improvements to Airline Flight Tracking: https://www.flightaware.com/news/article/FlightAware-Releases-Major-Improvements-to-Airline-Flight-Tracking/139 (checked October 2026)