International Airlines Group, formed by the merger of British Airways and Iberia, posted a strong rise in March traffic, boosted by continued growth in first and business class travel and a buoyant transatlantic market.
Traffic, measured in revenue passenger kilometres, rose by 6.2 percent versus March 2011, while passenger load factor was up 1 percentage point at 73.7 percent, it said on Wednesday.
IAG said its first and business-class travel - the most profitable part of its passenger business - rose 6.7 percent, while non-premium traffic was up 6.2 percent.
"Underlying market conditions at our London Heathrow hub continue to appear firm, in particular in the North Atlantic market," the company said in a statement.
"Our Spanish operations continue to be impacted by the ongoing threat of industrial action... and further deterioration of Spanish macroeconomic prospects in the short term."
Thirty days of strikes have been threatened between April and July in the company's Spanish operations, it said.
Earlier this year IAG said its under-performing Spanish unit and high fuel costs would dent 2012 earnings, after it reported a forecast-beating rise in 2011 profit.
On Tuesday industry body IATA said the outlook for airlines would be "fragile" in 2012.
IAG secured EU regulatory approval to buy Lufthansa's British regional airline bmi last week, after offering to give up 14 daily runway slots at Heathrow, Europe's busiest airport.
The acquisition was scheduled to complete around April 20 and then bmi would be integrated into BA, IAG said on Wednesday.