International aviation is about to face a crisis: a shortage of pilots. Domestically, regional carriers, which represent 42 percent of all passengers, are already canceling flights and eliminating service to smaller cities. Qantas, the largest carrier in Australia, is pulling old 747s out of mothballs because it doesn’t have enough qualified pilots for its 737s, the most dominate — and much more fuel efficient — aircraft in its fleet. Europe’s biggest airline, Ryanair, canceled thousands of flights last November because of inadequate staffing. Japanese airlines are so desperate for pilots they are raising the mandatory retirement age to 67.