The Civil Aviation Authority has warned of some delays to its Monarch repatriation fights due to weather and technical problems.
The UK regulator has also reassured Monarch customers that it has been in touch with 2,200 hotel and accommodation providers giving them financial guarantees.
This means customers covered by the Atol scheme should not have to pay again and should be able to continue with their holidays.
The CAA says it is “working round the clock” on the Monarch repatration, four days after the UK’s biggest airline failure.
The regulator’s flying programme completed 54 flights in its third day of operation on Wednesday, returning 11,287 people to the UK.
The CAA has charted a fleet of Qatar Airlines aircraft at a reported cost of £60 million to bring back all 110,000 Monarch customers.
With 11 days remaining and there are around 75,392 passengers still to bring back to the UK.
Today, the CAA plans to operate 58 flights, bringing over 10,793 people back to the UK.
Dame Deirdre Hutton, Chairwoman of the CAA, said: “Our flying programme to bring home 110,000 people from across the Mediterranean and beyond remains on course, with a total of 34,606 people already back in the UK.
“Our operation has thus far gone well and I am very pleased with the progress we have made during the first three days.
“However, this is a huge undertaking and we still have 11 days to go. Everybody at the CAA remains completely focused on this mission.
“Like any other airline, some of our aircraft have experienced delay, due to both technical faults and bad weather, resulting in frustration for some passengers.
“We’re very sorry and would like to apologise to anyone who has experienced a delay. I can assure you that we are doing everything within our power to deliver an on-time and efficient service.
“We have also been in contact with more than 2,200 hotel and accommodation providers giving them financial guarantees and ensuring Atol protected customers can continue their holidays unhindered.
“We will continue to work with hoteliers should there be any further concerns.
“Over the next 11 days we expect there to be many more challenges and we will continue to work around the clock with our partners to ensure all passengers are both given timely information about their return flight and flown home at no extra cost.”