Plane arrivals and take-offs at Britain's two biggest airports have been largely unaffected by Wednesday's strike.
However the RMT transport union reported "rock-solid strike action" that had led to "a total shutdown of key transport services in north-east England".
There were just a few cancellations of inbound transatlantic flights to Heathrow Airport on Wednesday morning.
Heathrow operator BAA, and its busiest carrier, British Airways, both reported near-normal services, with queues at immigration no longer than usual.
At the second-busiest UK airport - Gatwick in West Sussex - the first 22 inbound flights arrived as normal, with departures also running smoothly.
There has been fears that strike action by UK Border Agency (UKBA) staff would lead to chaos at Heathrow, where BAA had asked airlines to fly planes half-full.
A British Airways spokesman said: "We've had a positive start to the day and queues are pretty much as normal. There are reports that around two-thirds of the Border Agency staff are working at Heathrow."
A BAA spokesman said: "Due to the effective contingency plans we have put in place with the airlines and the UKBA over recent days, immigration queues are currently at normal levels. However, there still remains a possibility of delays for arriving passengers later in the day.
"As a result of the whole airport community working together over the past few days, we have more immigration officers on duty and fewer passengers arriving than would otherwise be the case. That puts us in a better place to avoid the serious delays and widespread disruption at Heathrow that were projected last week.
"We have deployed hundreds of additional customer services staff within our terminals. They are giving 24-hour support to passengers, providing information, food, drink and children's activity packs. They are equipped with iPads and BlackBerrys to keep passengers up to date."