"Extraordinary circumstances" is the airline's favourite phrase. It's often wrong.

It's the two-word answer that makes compensation claims disappear: the delay was extraordinary circumstances, so nothing is owed. Sometimes that's true. But the phrase has a precise legal meaning, the airline carries the burden of proving it, and a long line of court rulings has stripped away the excuses airlines like most. Here is where the line actually sits.

Excuses that have lost in court

• • Technical faults. The classic. Courts settled this years ago: keeping aircraft airworthy is the airline's ordinary business, so breakdowns, warning lights and parts found worn during checks are within its control, however unexpected. Only genuinely exceptional cases, like a hidden manufacturing defect grounding a whole fleet, or sabotage, qualify.
• • The airline's own staff striking. A strike by the airline's pilots or cabin crew is an internal labour dispute, ruled within its control. Wildcat strikes triggered by the airline's own restructuring announcement: same result.
• • "The inbound aircraft arrived late." Not a defence in itself. The airline has to show the original cause of the knock-on was extraordinary, and that it took reasonable measures to break the chain, like using a spare aircraft.
• • Crew out of hours, crew sickness, staffing gaps. Rostering resilience is the airline's job.
• • A bit of bad weather. Weather only counts when it actually prevented safe operation of your flight. If other airlines were landing on the same runway all afternoon, "weather" is a label, not a defence.

Excuses that genuinely hold

• • Severe weather that closed the airport or grounded operations across the board
• • Air traffic control restrictions and airspace closures
• • Strikes by airport staff, baggage handlers or ATC, people the airline doesn't employ
• • Security threats, medical emergencies and diversions, bird strikes
• • Political instability or official travel restrictions

Even then there's a second test: the airline must show it took all reasonable measures to avoid the delay anyway. An ATC restriction that cost 40 minutes doesn't excuse a 5-hour delay if the other 4 hours were the airline scrambling for a crew.

The burden of proof is theirs, not yours

You do not have to prove the delay was the airline's fault. The airline has to prove it wasn't, with evidence: weather reports for the actual airport at the actual time, ATC slot messages, technical logs. A refusal email that just asserts "extraordinary circumstances" with nothing behind it is a first offer, not a verdict. Reply asking for the specific cause and the evidence. A surprising number of refusals fold at that first push-back.

How to challenge a refusal

• • Check what actually happened: flight-tracking history shows whether other flights departed around yours, and where your aircraft had been that day. A "weather" delay that started three rotations earlier is a knock-on, not weather.
• • Ask the airline in writing for the specific cause and supporting evidence.
• • Still refused? Escalate to the relevant aviation dispute scheme or ombudsman, or hand it to a claims firm. They take a cut, but they know exactly which excuses collapse under scrutiny, and they'll take the airline to court when stonewalled. These weather-that-wasn't arguments are precisely the cases they win.