Air passenger numbers in the US are at their highest level since the COVID-19 pandemic set in.
Nearly 1.67m people were screened at US airport checkpoints on Sunday, the highest number since March 12 last year when air travel began to plummet, said the country's Transportation Security Administration (TSA).
However, it was still 35% below the number of airport travellers reported on the comparable Sunday in 2019, according to TSA figures.
Airlines in the US started to see an increase in bookings in mid-February and since March 11 this year the TSA has been screening at least a million people a day.
The rise in passenger numbers is attributed mainly to domestic travel since international travel to and from the US is still limited.
Vacation destinations have been the most popular, but business travel, which brings in more money for the airlines, is still at very low levels.
In a bid to boost the sector almost 50 US and UK travel industry groups have urged President Joe Biden and British Prime Minister Boris Johnson to lift restrictions on travel between the two countries.
In a letter on Monday, the groups said it would be ideal if the two leaders would announce "the full reopening of the US-UK air travel market for both citizens of both countries before the G7 meeting in early June.
Restrictions slowly lifted amid optimism
The Centers for Disease Control and Prevention says it is safe for vaccinated people to travel within the United States, although it continues to warn against travel to most foreign countries.
But given the fast pace of the US vaccination programme airline executives are cautiously optimistic for summer travel.
Last week, the TSA extended its requirement that airline passengers wear face masks.
That rule was set to expire May 11, but will now run through to mid-September.
Over the weekend, Delta Air Lines stopped blocking off middle seats. It was the last US airline to limit seating as a safety precaution.