Air traffic control staff shortages across Europe led to more than 11,000 Ryanair flights being delayed last month.
The Irish no-frills carrier blamed problems in France, Germany and Spain for the disruption to 11,346 flights, or 15% of the total, in October.
However, punctuality improved over the same month last year with 93% of flights arriving on time against 90% in October 2018.
Chief marketing officer Kenny Jacobs said: “Ryanair carried close to 14 million customers in October with over 93% of our 76,000 flights arriving on-time excluding ATC delays.
“ATC staff shortages and disruptions are still having a significant impact, delaying 15% of flights – with Germany, France and Spain as the worst ATC providers last month.
“Despite this, our punctuality is up both month-on-month and year-on-year.”
The airline also revealed that 87% of more than 168,000 passengers surveyed last month rated their flight as ‘excellent/very good/good’.
However, the boarding process was only rated highly by 83% while crew friendliness was top at 92%.