Normally U.S. airlines compete to sell tickets and fill seats during the peak summer travel season. But operators of the grounded Boeing 737 Max are facing a different problem: scarce planes and booming demand.

The grounding of Boeing Co¡¯s fuel-efficient, single-aisle workhorse after two fatal crashes is biting into U.S. airlines¡¯ Northern Hemisphere spring and summer schedules, threatening to disarm them in their seasonal war for profits.

¡°The revenue is right in front of them. They can see it, but they can¡¯t meet it,¡± said Mike Trevino, spokesman for Southwest Airlines Pilots Association and an aviation industry veteran.