The grounding of the 737 Max after two air disasters and the potential loss of TSA staff to the Mexico border means cancelled flights and long lines.

Summer living is supposed to be easy, according to George Gershwin, but millions of air passengers during this year's peak travel season may beg to differ thanks to a confluence of events that are making airlines and airports nervous.

The U.S. carriers' trade group, Airlines for America, estimates that a record 257.4 million people will fly from June 1 through the end of August, the tenth consecutive summer increase. Those throngs—totaling on average 2.8 million people each day—will confront two unique challenges: the possible reassignment of hundreds of aviation security personnel to the Mexican border, and the continued worldwide grounding of Boeing's 737 Max.

Airlines are expected to be robustly profitable during the summer season, a period when heavy demand keeps fares higher and planes fuller than during other parts of the year. But this year, all bets are off.

Regulators are still investigating the safety of the 737 Max following two crashes over five months that killed a total of 346 people. Three of the four largest U.S. carriers are grappling with how to cover their busy summer schedules with the loss of six dozen Boeing Co. 737 Max aircraft. The lack of those planes—which many airlines purchased to be their new workhorse of the skies—adds further pressure to carriers and customers at a time when the air travel system traditionally operates at full throttle.