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.
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