Officials from Heathrow and the Unite union are holding talks to avert strike action which would disrupt flights at the airport on Tuesday.
Monday’s strike at the UK’s biggest airport was called off late on Sunday and some airlines, such as British Airways, reinstated flights.
Even so, 16 flights were cancelled, including three by Lufthansa.
With a walkout of workers still scheduled for Tuesday, many more flights risk being cancelled.
Heathrow had initially cancelled 177 flights when the two-day strike action was announced.
- Heathrow flights cancelled as support staff strike looms
- Heathrow strike action suspended on Monday – BA reinstates flights
A total of 676 flights were scheduled for departure on Monday. While 16 were cancelled, five were moved to other London airports.
Talks are talking place at the conciliation service Acas over the pay deal, which Heathrow says is worth 7.3% over two-and-a-half years.
A Heathrow spokesperson said: “Unite have chosen to postpone their strike action today. Strike action on Tuesday 6 August is still scheduled to go ahead.
“We are continuing talks with Unite today and we remain hopeful that we can find a resolution and stop this disruptive and unnecessary threat of strike action.
“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.”
Once Monday’s strike was suspended, British Airways reinstated flights from Heathrow as did Air Canada, Aer Lingus, Etihad Airways, Flybe and TAP Air Portugal.
Virgin Atlantic moved flights from Heathrow to Gatwick.
‘Allow more time’
Among the airlines to cancel flights were Lufthansa and Swiss, which scrapped three each.
Lufthansa had booked 365 affected passengers on alternative flights.
Airlines are now waiting to learn of any developments from Monday’s talks with the union to decide what impact this will have on their schedules for Tuesday.
Heathrow’s website contains information for travellers about what to do strike days. Strikes are also scheduled for 23 and 24 August.
It recommends passengers should contact their airlines, both in the days leading up to their flight and before setting off for the airport.
“You may notice the airport is busier than usual,” Heathrow said, as there will be extra staff as substitutes for those on strike.
It also urged passengers, particularly frequent flyers, to allow more time to clear security.
“Our advice to every passenger is to be in the terminal at Heathrow two hours before your scheduled departure for UK and European flights, and three hours for all other flights, even if you already have your boarding pass before arriving at the airport and are only travelling with hand luggage,” Heathrow said.
Unite has about 4,000 members involved in the dispute.
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