One highlight of the Berkshire Hathaway AGM was that Buffett had exited airlines altogether. Warren Buffett even underlined that they had changed their view on airline stocks altogether. You are right that Berkshire had invested close to $7 billion into stocks like Delta, UAL, American Airlines and Southwest Airlines. In fact, Buffett owned nearly 10% in most of the large airlines. However, now Buffett is of the view that airline companies may be in for a troubled future as the economics of the business may have been structurally damaged. They are not positive on airlines any longer. A good chunk of the realized losses in the last quarter was due to the airline stocks. However, the overall net loss of $50 billion was largely attributable to the fact that Berkshire marks all investments to market.