(CNN) — London Heathrow, one of the world's busiest airports, has made the extraordinary move of asking airlines to stop selling tickets for outbound travel this summer.
Here's what you need to know about the measure.
Why is it happening?
Like many airports around the world, Heathrow has been struggling to cope with staff shortages and the surge in passenger demand following two years of pandemic disruptions.
Heathrow CEO John Holland-Kaye said in an open letter to passengers on July 12 that "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."
This temporary measure has been introduced as an attempt to minimize further disruption.
When does it start?
The cap is immediately effective from July 12 and will last until at least September 11.
I've already booked my ticket. What should I do?
You don't need to do anything. Your journey will go ahead as planned unless you are contacted by your airline with information to the contrary. Keep an eye on your email and text alerts and check the airline's app or website before you head to the airport.
If you wish to reschedule or to cancel your flight, check the airline's website for guidance.
"The airport will still be busy," said Holland-Kaye in the July 12 letter. "We ask you to bear with us if it takes a little longer to check in, go through security or collect your bag than you are used to at Heathrow. We ask passengers to help, by making sure they have completed all their Covid requirements online before they come to the airport, by not arriving earlier than three hours before their flight, by being ready for security with laptops out of bags and liquids, aerosols and gels in a sealed 100 ml plastic bag, and by using e-gates in immigration where eligible."
I'm transiting via Heathrow. Will I be affected?
Again, your flight will go ahead unless you hear otherwise from your airline. Keep a keen eye on updates as you prepare to travel.
What do I do if my flight is canceled?
Further disruptions are definitely in the cards, and some travelers will be affected by their flights being moved to another day, another airport, or being canceled altogether.
Passengers should be prepared to be flexible and for the eventuality that they may need to change their travel plans or have their flights refunded.
What disruptions have passengers been experiencing?
Last-minute flight cancellations have been a big problem this summer. In June 2022, they were up 188% on outbound flights from the UK, compared to June 2019, according to aviation analytics firm Cirium -- and that's despite scheduled flights being down 22% last month.
Holland-Kaye said in the open letter that while recruitment for the summer season began last November, "new colleagues are learning fast but are not yet up to full speed."
Ground handlers in particular are significantly under-resourced, said Holland-Kaye, explaining that they are the workers who "are contracted by airlines to provide check-in staff, load and unload bags and turnaround aircraft."
How do these numbers compare to pre-pandemic travel?
In 2018, the daily number of passengers going through Heathrow was nearly 220,000, split between arrivals and departures.
Can I still buy a ticket departing from Heathrow?
Heathrow's airline partners have been asked to stop selling summer tickets for unsold seats. So while it's still possible to snap up some last-minute flights, this window of opportunity will likely end soon and you run the risk of cancellation or disruption.
Fares are currently very high for these few remaining flights, due to the strong demand. We recommend that travelers seek alternative options.
What are the alternatives?
The UK capital is served by five other airports besides Heathrow: You can read our guide to them here.
Consider flying out of Britain's other airports -- Birmingham International is just over an hour from London Euston by train -- or traveling by rail or ferry.
When traveling this summer, aim to be flexible, travel early in the day if you can and purchase travel insurance.
Is just Heathrow that's affected or are other airports?
Amsterdam's Schiphol Airport last month became the first in the world to cap flights, but that move was in a bid to limit emissions. Analysis by the online travel agency Hopper has found that Brussels, Frankfurt International and Eindhoven are among the European airports currently experiencing the most delays, but it's been a widespread issue across the Western world as travel opens up more widely.
Holland-Kaye said in the open letter that "Similar measures to control passenger demand have been implemented at other airports both in the UK and around the world." This latest move may encourage other hubs to also take stronger action.
How are airlines responding?
A slot amnesty was implemented last month to encourage airlines to remove flights from the schedules without being penalized.
Holland-Kaye said in the letter that "some airlines have taken significant action, but others have not, and we believe that further action is needed now to ensure passengers have a safe and reliable journey."
CNN has reached out to British Airways, the UK's flag carrier which has its home base at Heathrow, for comment on the situation.