British Airways, hindered by cabin crew strikes, carried 14.6% fewer passengers last month than in March 2009.
The airline carried just under 2.3 million passengers last month down from the March 2009 total of just over 2.6 million.
BA attributed half of the decline to winter capacity reductions and half to the strikes which saw cabin crew walk out from March 20-22 and March 27-30.
The decline last month was most marked in the Asia Pacific sector, which was down 25.3% compared with March 2009.
UK and Europe traffic fell 18.6%, while Africa and Middle East flight passenger numbers were down 10.3% and traffic to North and South America (including the Caribbean) was down 3.7%.
BA planes flew 74.7% full last month - an increase of 2% on the March 2009.
BA said the total impact of the strike action last month was estimated to be £40m to £45m.
BA said that over the first strike weekend last month it operated 78% of its long-haul programme and 50% of short-haul flights.
For the second strike weekend these figures rose to 83% and 67% respectively. For the seven days of strikes the airline operated 79% of long-haul flights and 58% of short-haul.
Economy-class passenger numbers were down 12.2% last month, while premium traffic (first-class and business-class) declined 7.2%.
The Unite union, representing the cabin crew, pledged not to take any action over Easter and is yet to announce any further strikes.
The dispute, over cost-cutting and jobs, remains deadlocked with little sign of an early breakthrough.
Meanwhile, low cost airline Ryanair today announced it flew 5.3 million passengers last month - a 13% increase on the March 2009 figure.
Ryanair's planes flew 79% full in March 2010 - a two-point rise on the same month last year.
Ryanair have also announced a new route from Kerry Airport to Dusseldorf-Weeze in Germany, which is also close to the Dutch border.
