Flight delay reasons: which causes mean the airline owes you

The gate screen changes for the third time. "Delayed - operational reasons." Nobody at the desk can tell you more. Four hours later you land, too tired to argue, with a dinner booking, a hotel night and a morning meeting already written off.

That vague line on the screen matters more than most passengers realise. Under EU and UK law, the reason for your delay decides whether the airline owes you €250 to €600 in cash or nothing at all. Airlines know this. It's why so many delay notices stay deliberately fuzzy, and why so many rejection emails reach for the word "extraordinary".

At Gyro, we test those explanations every day across more than 40 jurisdictions. Plenty of them don't survive contact with the evidence. Here is what really makes flights late, which reasons the law treats as the airline's problem, and how to tell when you're owed money.

What are the main reasons flights get delayed in Europe and the US?

Flights rarely run late for one dramatic reason. Most delays start small: a slow turnaround, a missing crew member, a tight slot through busy airspace. Then they snowball through the rest of the aircraft's day.

Both sides of the Atlantic track this closely. Airlines in Europe attach a standard IATA delay code to every late departure. Eurocontrol's Central Office for Delay Analysis then groups those codes into a handful of causes. Its latest annual digest shows how the average delay per flight breaks down.

Source: Eurocontrol, CODA Digest Annual 2024 (published July 2025). The "Everything else" row is the remainder of the 17.5-minute total.

The picture improved in 2025 without changing shape. Average departure delay fell to 14.6 minutes per flight, according to Eurocontrol's 2025 European Aviation Overview. Reactionary delay stayed the top reason even after a 19% drop. Eurocontrol's Performance Review Commission puts it neatly: every minute of primary delay generated another 0.79 minutes of knock-on delay later in the day.

The US data, which we break down further on, tells almost exactly the same story.

The headline categories hide the detail that matters for a claim, though. "Airline" covers everything from a late fuel truck to a cracked windscreen. "Reactionary" only tells you the trouble started somewhere else. When we build a claim, the first job is always to dig one level deeper than the label.

Can you claim compensation for a knock-on delay caused by an earlier flight under EC 261?

A knock-on delay happens when your aircraft arrives late from its previous trip. Your flight inherits that lateness, plus any time lost to crew duty limits and missed slots. Airlines often call it "late arrival of the inbound aircraft", as if that settles the matter.

It doesn't. The law looks straight through the knock-on effect to whatever started the chain. In Transportes Aéreos Portugueses (C-74/19), the Court of Justice of the EU ruled that an airline may rely on an extraordinary circumstance that hit an earlier flight flown by the same aircraft. It must, however, prove a direct causal link between that event and your delay.

So everything depends on the first domino:

• The morning flight was held by a thunderstorm or an air traffic control restriction. The airline may have a defence for your evening flight too, if it can show the chain clearly.
• The morning flight was late because of a technical fault, a slow turnaround or a crew problem. The knock-on delay is still the airline's responsibility. Compensation stays on the table.
• The schedule had no slack and simply ran out of time. That's a planning decision, not an event beyond anyone's control.

When an airline tells us a delay came from the inbound aircraft, our next question is always what delayed the inbound aircraft. Quite often the trail ends at a maintenance check or a crew swap several sectors back. Those claims stay very much alive.

Do technical problems with the aircraft count as extraordinary circumstances under EC 261?

Almost never. Technical faults are among the most common reasons airlines give for long delays. Yet they make one of the weakest legal defences. To refuse payment, an airline must prove that extraordinary circumstances under EC 261 caused the delay and that all reasonable measures couldn't have prevented it.

The Court of Justice set the rule in Wallentin-Hermann (C-549/07) back in 2008. A technical problem found during maintenance, or caused by a failure to maintain the aircraft, is part of an airline's normal activity. In van der Lans (C-257/14), the court went further. A part that fails out of the blue, despite proper maintenance and routine checks, still doesn't count.

There are narrow exceptions. A hidden manufacturing or design defect that the manufacturer or an aviation authority reveals can qualify, as can damage caused by an outsider, such as debris on the runway. Think of the line this way: if the problem lives inside the airline's hangar, it's the airline's problem.

Rejection letters that cite a "technical issue" rarely survive a request for detail. Ask the airline which component failed and whether the fault surfaced during a check or came from a manufacturer's warning. A vague or slow answer is usually good news for your claim.

Is a flight delayed by crew shortages or an airline staff strike eligible for compensation?

In most cases, yes. Staffing is part of the job of running an airline. The courts have been strict about that for years.

The starkest example came in 2023. A TAP Portugal co-pilot was found dead in his hotel less than two hours before departure. The shocked crew declared themselves unfit to fly. Even so, the Court of Justice ruled that the unexpected absence of an essential crew member, through illness or death, is inherent in an airline's normal activity. If a sudden death doesn't qualify, a pilot calling in sick won't either.

Strikes split into two camps:

• Strikes by the airline's own staff usually mean compensation. In Krüsemann (C-195/17), a "wildcat" wave of sick calls after a surprise restructuring announcement didn't count as extraordinary. In Airhelp v SAS (C-28/20), neither did a lawful pilots' strike called by a union.
• Strikes by outsiders usually don't. The European Commission's Your Europe guidance treats strikes external to the airline, such as air traffic controllers or airport staff, as potentially extraordinary.

UK passengers should note one wrinkle. UK courts follow EU rulings made before Brexit took full effect at the end of 2020. That brings Krüsemann into UK261 claims. The SAS and TAP rulings came later, which means UK judges can weigh them without being bound by them.

Airlines sometimes file staff shortages under "operational reasons" or even "air traffic control". If one airline cancelled dozens of flights on the same day while its rivals flew normally, that's a strong hint the problem was internal.

Does bad weather mean the airline doesn't have to pay compensation for a delayed flight?

Sometimes, but far less often than airlines suggest. EC 261 itself names weather that's incompatible with operating the flight as a typical extraordinary circumstance. A blizzard that shuts the runway or thunderstorms parked over your destination will usually qualify.

The word "weather" on a delay notice is still a claim, not proof. The airline has to show that the weather actually hit your flight and that reasonable measures couldn't have avoided the delay. Watch for these gaps:

• The storm passed hours before you were due to leave. The airline then has to explain why its recovery took so long.
• Other airlines flew the same route close to schedule. That undermines the idea that conditions made flying unsafe.
• The conditions were routine for the season. An ordinary winter de-icing queue is much harder to pass off as extraordinary than a once-a-decade storm.

If snow is the culprit, our guide to what airlines owe after a winter storm cancellation walks through the rulings that tip those cases either way. And remember that weather never cancels your right to care. When volcanic ash grounded Europe in 2010, the Court of Justice later confirmed in McDonagh (C-12/11) that airlines still had to provide meals and hotels.

The weather claims we win usually share one feature: the clock. When the airline's own timeline shows the aircraft sitting ready long after the weather cleared, the defence starts to wobble.

Is an air traffic control delay or ATC strike the airline's responsibility under EC 261?

Generally, no. Recital 15 of EC 261 says an air traffic management decision affecting a particular aircraft on a particular day counts as extraordinary. Strikes by air traffic controllers fall outside the airline's control as well.

This cause is real. It's just smaller than its reputation. Europe's en-route air traffic flow delay averaged just 1.7 minutes per flight in 2025, down 21% on 2024, according to Eurocontrol. Strikes were also less disruptive in 2024 than in 2023, when French controllers' industrial action hit nine months of the year.

The catch is arithmetic. In Pešková (C-315/15), the court ruled that only the time actually caused by an extraordinary event is excused. Any extra delay from ordinary causes still counts towards the 3-hour threshold. A 50-minute air traffic slot, for example, can't explain a flight that lands four hours late.

Air traffic flow restrictions are logged, which means they can be checked. When the timing of a restriction doesn't line up with your departure, or only covers a fraction of your delay, the airline's defence falls apart.

Which other flight delay reasons count as extraordinary circumstances under EC 261 and UK261?

A handful of events sit genuinely outside an airline's control. The courts have accepted several of them:

• Bird strikes. Pešková (C-315/15) confirmed they're extraordinary. However, if the airline insists on a second safety check after an authorised engineer has already cleared the aircraft, the extra time is on the airline.
• Debris or fuel on the runway. A stray screw that burst a tyre counted in Germanwings (C-501/17). So did spilt fuel that closed a runway in Moens (C-159/18).
• Unruly passengers who force a diversion. Transportes Aéreos Portugueses (C-74/19) accepted this, unless the airline contributed to the behaviour or ignored clear warning signs at boarding.
• Security threats and political instability. Both appear in EC 261's own list of typical examples.
• Medical emergencies on board. From October 2027 these join the official list. Until then, courts weigh them case by case.

Not everything that looks like bad luck qualifies, though. In Siewert (C-394/14), mobile boarding stairs crashing into the aircraft was ruled part of normal airport operations. The airline still had to pay.

Of these, "bird strike" is the label we test hardest. We ask whether the strike hit your flight or an earlier one, and how long the inspection really took. The answer often leaves hours of delay that no bird can explain.

Which flight delay reasons qualify for EC 261 and UK261 compensation?

Here is how the most common reasons usually play out once you strip away the airline's wording. Every verdict assumes the airline still has to prove all reasonable measures were taken.

Source: Regulation (EC) No 261/2004, recitals 14 and 15; Court of Justice of the EU judgments as cited. Under UK261, Airhelp v SAS (2021) and TAP Portugal (2023) are persuasive rather than binding.

If your delay crossed 3 hours and the reason falls in a "yes" row, the amount depends on distance. Under EC 261 that means €250 for flights up to 1,500 km, €400 for most flights between 1,500 and 3,500 km and €600 beyond that. The UK Civil Aviation Authority applies the same bands under UK261 at £220, £350 and £520.

Treat the table as a starting point, not a verdict. Two delays with the same label can end very differently once the timeline is laid out, which is exactly the work we do on every claim.

What do US airlines report as the reasons for flight delays, and what are you owed under DOT rules?

US airlines report every delay of 15 minutes or more to the Bureau of Transportation Statistics, sorted into five cause categories. The 2026 figures so far look remarkably like Europe's.

Source: BTS Airline On-Time Statistics and Delay Causes, January to August 2026, all reporting carriers. Over the same period, 74.66% of flights arrived on time, 2.27% were cancelled and 0.33% were diverted. Share of delayed flights is a Gyro calculation from the BTS figures.

One quirk deserves a mention. The BTS weather category only covers extreme weather. Everyday rain, wind or low cloud that slows air traffic control gets filed under the National Aviation System instead. Weather's true share is therefore bigger than 0.88% suggests.

What you're owed in the US is much thinner than in Europe. There's no federal cash compensation for delays, even when the airline is at fault. The Department of Transportation formally withdrew its proposal for one in November 2025. Two protections still matter:

• A refund if you don't travel. If your flight's arrival or departure moves by 3 hours or more domestically, or 6 hours internationally, and you decide not to fly, the airline must refund you. That applies whatever caused the delay.
• Meals and hotels for delays the airline controls. On the DOT's Airline Customer Service Dashboard, the major carriers list their commitments, such as a meal or voucher once you've waited 3 hours and a hotel for an overnight delay. Commitments vary by airline. DOT still expects each one to honour what it publishes.

Flying between the US and Europe? EC 261 covers every flight departing an EU airport and flights into the EU on an EU airline. A delayed Lufthansa flight from New York to Frankfurt can therefore pay up to €600.

When a US airline admits a delay was its own doing, its dashboard promises kick in. Ask the gate agent directly whether the delay is "controllable". That one word can decide whether you get a meal voucher or a shrug.

How will the EU261 reform change the reasons airlines can use to refuse compensation?

The rules on delay reasons are about to get much more specific. Regulation (EU) 2026/2202 was published in the EU's Official Journal on 2 October 2026 and applies from 23 October 2027. Until then, today's EC 261 and the court rulings above govern every flight.

The compensation itself barely moves. Amounts stay at €250, €400 and €600. Compensation is due when you arrive more than 3 hours late. What changes is how an airline has to defend a refusal:

• A legal definition. An extraordinary circumstance must be both outside the airline's normal activity and beyond its actual control.
• A non-exhaustive list. The annex covers events such as weather incompatible with safe flight, air traffic restrictions and airspace closures, strikes at airports, air navigation providers and ground handlers, hidden manufacturing defects, unruly passengers and medical emergencies, security threats, and damage by third parties or wildlife.
• A narrower strike rule. A strike at the airline only counts when the strikers' demands are ones the airline itself can't meet, such as changes only public authorities can make.
• A direct causal link. The airline must prove the event caused your specific disruption and that all reasonable measures couldn't have avoided it.
• A named reason. Within 30 days of your claim, the airline must pay or explain its refusal, naming the exact circumstance it relies on.

There's a catch for passengers too. Claims must reach the airline within nine months of the flight. UK261 isn't part of this reform. UK flights keep today's rules and today's longer limitation periods.

The nine-month window is the change we'd circle in red. Right now, most passengers can still claim years after the flight under national time limits. From late 2027, anyone who waits risks losing an EU claim they would otherwise win.

How do you find out the real reason your flight was delayed?

The airline won't always volunteer the truth. Collect it yourself while you're still at the airport. Five minutes of effort at the gate can be worth hundreds of euros later.

• Ask for the reason in writing. Note the exact words used at the desk and screenshot every app notification and email.
• Photograph the departures board. Capture the delay, the stated reason and the time.
• Note your aircraft's registration. Flight-tracking sites show which aircraft flew your route and how late its previous trip landed.
• Check what other flights did. If other airlines left on time from the same airport, a weather excuse looks shaky.
• Record the time the doors opened at your destination. That's the arrival time compensation is measured against.
• Keep every receipt. Meals, taxis and hotels you paid for are claimable on top of compensation.

When the airline replies, ask it to name the event, the flight it affected and the measures it took. If it still refuses and the explanation doesn't hold up, escalating to the right regulator or enforcement body is the next step, whether that's a national enforcement body in the EU, a CAA-approved dispute scheme in the UK or the DOT in the US.

The single most useful detail is the aircraft's registration. With it, we can trace the inbound flight, spot knock-on delays and test whether the airline's story holds together. It takes seconds to note and can save weeks of back and forth.

So which flight delay reasons actually get you compensation?

More of them than airlines would like you to believe. The two biggest causes of delay on both sides of the Atlantic are knock-on effects and the airline's own operations. Those are precisely the categories most likely to end in a payout. Weather, air traffic control and security events are real. They simply account for a smaller share of delay than their reputation suggests. Even then, the law only excuses the time they actually caused.

That leaves you with a simple rule. Treat every explanation as the airline's opening position, not the final word. Pin down what started the chain of delay, check the timeline and remember that the burden of proof sits with the airline. You may also have a separate claim under the Montreal Convention for proven losses, such as a missed hotel night, if the airline can't show it took all reasonable measures.

Don't wait for the 2027 reform to tighten the clock either. If a flight in the last few years landed 3 hours or more late, we'll check what caused it and what it's worth for free. Start a claim with Gyro. Or connect your inbox to Autopilot and we'll scan three years of flights for compensation you didn't know you were owed.

Find out if your delay reason pays

If your flight landed 3+ hours late, you may be owed €250 to €600 under EC 261 or £220 to £520 under UK261, or potentially more under the Montreal Convention. Gyro checks your eligibility for free. You keep 100% of whatever the airline pays.

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