According to Cirium’s On-Time Performance Review 2021, December was the biggest month for air travel in 2021, with 2.43 million flights globally.

The Omicron variant’s arrival late last year and operational challenges, including winter weather, resulted in 59,240 global flights being cancelled from December 24 to January 3—the highest number of December cancellations in a decade. Some 20,500 flights were cancelled in just three days on New Year’s Eve and Day.

American Airlines, Delta, Southwest Airlines, and United Airlines all cancelled more than 7,000 flights in the United States during this period. A lack of staffing hampered crew and ground operations.

A week before the onset of Omicron on December 11-17, 2021, Cirium reported an increase of 1.5% in worldwide flights flown week-over-week. Yet, Cirium reported an 8.0% decrease in global flights flown the following week.

Last year’s most popular month for air travel was December, according to Cirium.

Jeremy Bowen, CEO at Cirium, commented:

“Flight disruptions affect airlines and airports differently – it depends on the availability and flexibility of equipment and resources in place to react quickly. Those that plan more conservatively will minimize their operational disruptions. Cirium monitors the level of disruption by measuring completion factor of flights and their on-time performance.”

According to the data, American Airlines had the most flights last year, with around 1,850,050. With 336,890 departing flights in 2021, Hartsfield-Jackson Atlanta International Airport was named the busiest worldwide airport, while Amsterdam Airport was named the busiest airport for international flights, with 123,070 departing flights.

Meanwhile, Heathrow has urged the UK government to discontinue testing for fully vaccinated travellers, citing reports that 60,000 people cancelled flights from the airport last month owing to the impact of Omicron.

Airlines in Europe are also likely to cancel tens of thousands of flights this month and next, with the Lufthansa Group alone cancelling 33,000 flights in the following weeks.