The Transportation Department said its investigation found that Southwest operated two chronically delayed flights — one between Chicago Midway International Airport and Oakland, California, and another between Baltimore, Maryland, and Cleveland, Ohio.

The unions are calling Tuesday’s protests a national day of action. It is not a strike — federal law makes it difficult for airline unions to conduct legal strikes.

After rediscovering the old photo, the father and son added a goal: not only did they want to fly together, they wanted to recreate the 1990s flight deck photo, over two decades later. Not just as father and son, but as colleagues and co-pilots.

There are also mounting requests to more aggressively and comprehensively address the air travel system’s bottlenecks, including obsolete technology and staffing issues.

DaJuan Martin, 36, was charged in Chicago’s federal court Monday with 12 counts of wire fraud stemming from the alleged fraud scheme. A second man, 46-year-old Ned Brooks, was also charged with four counts of wire fraud after he allegedly purchased several of these fraudulent vouchers.

Southwest canceled about 16,700 flights over the last 10 days of December. The U.S. Department of Transportation is investigating whether the airline deceived customers by knowingly scheduling more flights than it realistically could handle.

Southwest Airlines returned to a relatively normal flight schedule Friday, as the focus shifts to making things right with what could be well more than a million passengers who missed family connections or flights home during the holidays, and many of whom are still missing luggage.

It is likely that far more than 1 million passengers have been affected. Southwest has canceled more than 13,000 flights since its meltdown began on Dec. 22. Its planes have 143 to 175 seats and were likely nearly fully booked around the Christmas and New Year’s holidays.

This week, with cancellations from other major airlines ranging from none to 2%, Southwest has canceled nearly 10,000 flights as of Wednesday and warned of thousands more Thursday and Friday, according to FlightAware.

Airports most affected by the Tuesday cancellations are Denver International, followed by Chicago Midway International, Baltimore/Washington International, Harry Reid International Airport in Las Vegas, Dallas Love Field and Nashville International.