New Delhi,  Air travellers are facing chaos across the globe. Since May, US airlines have cancelled more than 21,000 flights, or about 2.7 per cent of the scheduled total.

Winding queues and piles of abandoned luggage are becoming an increasingly common sight in airports across Europe, Euro News reported.

Airlines have cancelled tens of thousands of flights since May, leaving passengers stranded, while airports have struggled with industrial action and technical glitches.

The July 4 weekend -- an American holiday -- has seen hundreds of flights cancelled and more than 12,000 delayed.

However, the number of cancellations still pales in comparison to the European total.

Europe had more than double the cancellations of US carriers between April and June, data from flight tracking company RadarBox.com revealed, Euro News reported.

Between April 1 and June 29, Europe's top 10 worst performing airports cancelled a mammoth 64,100 flights.

The reason has partly to do with staffing. US airlines also slashed staff during the pandemic, making 90,000 workers redundant. However, most American carriers -- including big hitters American, Delta, United and SouthWest -- started recruitment in the middle of 2021, in line with the return of domestic travel.

Another key point is that due to less vigorous and varying Covid restrictions between states, US flight numbers didn't drop as significantly as those in major European countries, Euro News reported.

European airports are struggling to cope with an extreme staffing deficit.

At the peak of the Covid-19 pandemic, airports and airlines made roughly 191,000 European aviation workers redundant.

According to a study published in January 2021 by the European Transport Workers Federation, 58.5 per cent of airport ground staff were at work at the time. At least 23 per cent of them were made redundant, Euro News reported.

Airports like Heathrow and Schiphol have begged airlines to cut flights, while many carriers have been forced to pre-emptively cull their schedules by thousands of trips.

"Making these cancellations is not something we take lightly," former Chief Operating Officer of easyJet, Peter Bellew, had told the staff after cutting dozens of flights.

Heathrow Airport earlier this month introduced an unprecedented 100,000 limit on daily departing passengers until September and ordered airlines to stop selling summer tickets as the airport battles against a staffing crisis, Daily Mail reported.

The dramatic move will impose a maximum limit on the number of passengers allowed to leave the airport between July 12 and September 11.

Airlines had planned to operate flights with a daily capacity averaging 104,000 seats over that period -- meaning further cancellations are likely, Daily Mail reported.

Heathrow said it has ordered airlines to "stop selling summer tickets to limit the impact on passengers".

The measure will lead to more cancellations on top of the thousands of flights axed in recent months.

Passengers have been hit by delays and cancellations at airports across the UK due to a shortage of staff after thousands were laid off or left the industry during Covid, Daily Mail reported.

Announcing the passenger cap, Heathrow Chief Executive John Holland-Kaye said: "Over the past few weeks, as departing passenger numbers have regularly exceeded 100,000 a day, we have started to see periods when service drops to a level that is not acceptable."

Problems include long queue times, delays for passengers requiring assistance, bags not travelling with passengers or arriving late, low punctuality and last-minute cancellations, Holland-Kaye said, Daily Mail reported.

Emirates airline blasted one of the world's busiest airports for its "incompetence" in failing to handle a surge in passengers, CNN reported.

The Dubai-based airline slammed demands made by London's Heathrow airport earlier this week that carriers stop selling any more tickets for this summer.

The airline, which operates six daily flights from Heathrow, has rejected the new limits and called them "entirely unreasonable and unacceptable", CNN reported.

Heathrow, like other airports, has struggled to cope with a bounce back in travellers after two years of pandemic restrictions and staff cuts. The airport said on Tuesday that it would cap daily passenger numbers at 100,000 until September 11.

"Heathrow chose not to act, not to plan, not to invest. Now faced with an 'airmageddon' situation due to their incompetence and non-action, it is pushing the entire burden - of costs and the scramble to sort the mess - to airlines and travellers," the airline said in a statement, CNN reported.