No industry has a higher pain threshold than aviation. It staggers from crisis to crisis, making profits in the good years, only to lose it all again when things go wrong — which they inevitably do. For example, the industry lost $10 billion in the early 1990s during the Gulf War. Then, after September 11, it lost more money than it had made in its entire history up to that point. Then, the losses from the Great Recession were even greater again.  But the last two years have been the worst ever for the industry. The losses from Covid-19 are…