But the travel operator said its first half loss narrowed despite the setback.
Thomas Cook reported a pre-tax loss for the half year to March 31 of £252.2m compared with £309m the year before.
Northern European airspace was shut down for six days last month after Iceland’s Eyjafjallajökull volcano erupted, spewing ash into the air.
Thomas Cook said that – excluding the estimated impact of the volcanic ash cloud – it was confident of meeting expectations for the full-year.
Its shares have dropped by ten per cent since the disruption began.