The U.K.'s flagship carrier said in a statement Monday that it had "no way of predicting how many (pilots) would come to work or which aircraft they are qualified to fly."
As a result, it said it had "no option but to cancel nearly 100%" of its flights for the duration of the strike.
British Airways operates up to 850 flights a day. London's sprawling Heathrow Airport was most affected by the work stoppage as it is the airline's hub and is used for many of the company's long-haul international flights.
The sprawling departure area at Heathrow Terminal 5 was almost empty, with only a handful of BA flights set to leave on Monday.
There were no queues at any of the check-in desks or security gates and only a handful of people waiting on benches. The terminal is typically quite busy.