The five official causes
The Bureau of Transportation Statistics classifies every delay into five categories:
- Carrier (38%) — The airline's fault: maintenance, crew, cleaning, baggage loading, fueling
- Late Aircraft (36%) — The inbound plane arrived late. This is the cascade effect in action.
- NAS / Air Traffic (16%) — Air traffic control restrictions, airport congestion, runway closures
- Weather (9%) — Only directly weather-caused delays. Many weather-affected delays are classified as NAS.
- Security (1%) — TSA, terminal evacuations, security breaches. Rare.
Why this matters for compensation
Carrier delays and late aircraft are the airline's responsibility — these qualify for EU261 compensation. Weather and NAS generally don't (extraordinary circumstances). Security is case-by-case.
The trick: "late aircraft" is often caused by a carrier issue earlier in the chain. If the original delay was the airline's fault, you may still qualify for compensation even if your specific delay is classified as "late aircraft."