"We can already see now that the coming summer will be a challenge for us all," managing director Oliver Lackmann said in advance abstracts of a story due to run in Berlin daily Tagesspiegel on Monday.

"We still have bottlenecks in air-traffic control, and we see further logistical difficulties at the airports at the same time that air travel is growing," he said.

The German Aviation Association BDL also warned of further delays and cancellations in an online briefing on Thursday.

Strikes and bad weather also contributed to backlogs last year, leading to costly compensation claims from passengers that burdened the airlines already struggling with lower ticket prices and ruinous competition.

Lackmann said that to limit problems TUI fly has booked replacement capacity and together with tourism company TUI Deutschland, another subsidiary of the TUI group, has reserved maintenance capacity for the summer.

He said negative external factors could nevertheless not be ruled out.

German airline companies agreed at a summit last October on measures to tackle the problems in the industry such as ensuring more reserve aircraft are on hand and launching hiring and training drives.

Another industry summit has been scheduled for March 28 in Hamburg to review the success of the measures so far.

(Reporting by Vera Eckert; Editing by Hugh Lawson)