Regional airline Flybe, which flies to 15 destinations from Belfast City Airport, said slowing consumer demand and over-capacity sent it swinging to a loss last year.
The firm posted a £19.9m pre-tax loss in the year to March 31, compared to a profit of £2.7m for the previous 12 months.
This was despite revenue increasing 13.4% to £707.4m.
Flybe said: "Despite the substantial progress in reducing legacy fleet orders in 2015/16, Flybe has still seen significant capacity growth in a market where we witnessed slower growth in consumer demand.
"New routes and increased frequencies were targeted to cover marginal costs in the early years of operation, but do not contribute significantly to overall profitability. The capacity growth therefore had a negative effect on profitability."
The firm was also stung by a £4.8m write-down linked to an IT upgrade.