Brooks Nader was minutes away from taking off for a little college football fun ... but the Federal Aviation Administration had other plans, grounding her private flight amid a nationwide shutdown Friday ... TMZ has learned.

Sources close to Brooks tell TMZ ... she was literally about to take off from New York to her home state of Louisiana for the LSU game when the FAA ordered all departing flights across the country to remain grounded.

We're told Brooks is safe but stuck sitting on the tarmac ... and the pilots have zero updates about what's going on. Our sources say it's now looking very unlikely her plane will get off the ground tonight.

Meanwhile, fitness model Jen Selter tells TMZ she's dealing with a very different situation ... she's already in the air!

Jen tells us her flight took off about an hour before news of the nationwide ground stop broke ... and she had no idea what was unfolding when we first reached her.

Despite the chaos on the ground, Jen says things have remained calm in the sky. She tells us the pilot has been extremely calm and professional while providing updates, and passengers have kept their cool.

We're told the pilots informed passengers on Jen's flight they're still figuring out exactly what's happening, but they believe the flight will most likely be able to land as planned in Scottsdale.

As we reported ... the FAA issued the rare nationwide ground stop Friday after a communications issue impacted air traffic control centers across the country.

Transportation Secretary Sean Duffy confirmed FAA technicians were investigating the issue.