The Heathrow Terminal 5 debacle hit British Airways' monthly passenger figures for March 2008.
Despite the benefit of an early Easter, BA carried just under 2.72 million passengers last month - a 2.8% dip on the March 2007 total.
BA said the financial impact of the events surrounding the T5 opening - with dozens of flights cancelled and thousands of bags still not back with passengers - was "estimated to be around £16 million".
The cancellation of flights at T5 have been centred on domestic and short-haul European routes.
BA's UK and European passenger levels fell 2.8% last month, while passenger numbers to North and South America were 0.6% down, with Asia Pacific down 6.0% and Africa and the Middle East down 5.7%.
Premium traffic - the number of passengers travelling in first and business class seats - was down 5.0% last month while non-premium (economy-seat) traffic fell 2.3%.
BA planes travelled 75.4% full last month compared with 76.3% in March 2007.
BA said: "The figures also reflect the events which surrounded the opening of Terminal 5 on March 27. The impact was borne by the short-haul schedule, where there were 300 cancelled flights, equating to 0.2% of capacity. The financial impact of these events is estimated to be around £16 million."
BA said it would operate a full schedule of flights on Saturday when the number of flights due to take off and land is lower than on weekdays.
Baggage handlers are still sorting through 14,000 pieces of luggage lost in the chaos as flights took off with passengers but no bags on board. Bags being returned to addresses in mainland Europe have already been sent to Milan where they are being sorted by a contractor, reducing the original 18,000-piece bag mountain.
