Tui Group saw turnover increase by eight per cent, to €3.8 billion, in the first quarter.
However, underlying profits fell by 77 per cent, to a €147 million loss, in the three months to December 31st.
Net debt increased sharply, by 177 per cent to €5 billion.
Tui was also forced to cut its earnings estimate for 2020 – largely due to the ongoing grounding of the Boeing 737 Max.
While initially expecting the plane to return to service in April, the deadline might now slip until the summer.
As a result, the FTSE 100-listed travel operator now forecasts full-year underlying earnings will be between €850 million and €1.05 billion.
This is opposed to previous guidance of between €950 million and €1.05 billion.
The extra expenses incurred by the grounding are expected to be offset by compensation by Boeing and “strong trading” in the markets and airlines division.
The new year started “exceptionally well” in terms of bookings, Tui added, with the UK posting a record month.
Shares in Tui were up nearly 12 per cent in early trading following the release of the figures.