Dozens of Heathrow flights were cancelled on Monday despite the suspension of a planned strike by the airport’s workers.
Thousands of air passengers suffered disruption as 37 of the day’s departures and arrivals were cancelled, representing around 3% of all flights.
This is despite Monday’s strike being suspended on Sunday night to allow further talks on resolving a pay dispute at the UK’s busiest airport.
A 24-hour walkout is still scheduled to take place on Tuesday.
Airlines affected include Virgin Atlantic, American Airlines, Air France and Qatar Airways.
Around 177 flights across all airlines were initially cancelled on Monday and Tuesday.
British Airways reinstated its Monday flights, but some of the carrier’s passengers reported being warned there would be a “significantly reduced catering offering” due to the “late postponement” of the strike.
Virgin Atlantic said it would continue with its plan to switch a small number of flights to Gatwick.
Passengers are being urged to check with their airline for updates.
Members of the Unite union were due to walk out from one minute past midnight on Monday for 48 hours.
The two sides met throughout the weekend under the chairmanship of the conciliation service Acas, and further talks will take place on Monday.
Unite said on Sunday that talks will involve senior directors from Heathrow and senior officials from the union “with the aim of averting a second day of planned strike action”.
The union’s members, including security staff, firefighters and engineers have voted against a pay offer Heathrow said was worth 7.3% over two-and-a-half years.
Heathrow said in a statement: “We remain hopeful that we can find a resolution and stop this disruptive and unnecessary threat of strike action.
“Airlines may choose to reinstate impacted flights.
“We regret that passengers have been inconvenienced by this and urge them to contact their airline for up-to-date information on the status of their service.”
On Tuesday’s planned strike, Heathrow said it has been working with airlines to identify departures which will need to be cancelled.
The statement added: “While the vast majority of flights will be unaffected, some airlines are making arrangements to operate flights from other UK airports, others will be delaying flights and unfortunately a number will be cancelled.
“Airlines have now started to contact passengers on affected flights and passengers should contact their airline for more information.
“We recommend passengers check their flight status before travelling to the airport and read the guidance on heathrow.com to prepare for their journey.”