Jessica Simpson, Eric Johnson Land in Sin City, Mum on Reconciliation

5:35 PM PT -- Jessica Simpson and Eric Johnson have officially touched down in Las Vegas after they were spotted together on a flight earlier on Friday.

The pair, who announced their separation earlier this year, stayed tight lipped on any possible reconciliation ... though, EJ issued a slight smile when someone declared it was good to see them out and about together.

Viva Las Vegas!!!

Jessica Simpson and Eric Johnson have been separated for a while now, but there are signs of a reconciliation in the air.

Check out JS and EJ boarding a Southwest Airlines flight Friday afternoon from Burbank to Las Vegas. The first thing we thought ... maybe it's a vacay with their kids, but there were no kids in sight.

They sat next to each other on the flight -- yeah, we wondered too why they weren't flying private.

We've got a good idea why they're in Sin City ... they're catching Ashlee Simpson's show at the Venetian. It's the first night of her residency.

That's especially interesting ... why Eric would be there with Jessica if it's a Simpson family event, but there he was. We assume he's attending the show, too, and not just escorting Jess to the venue, and then waiting outside.

They announced their separation in January but they've been apart for much longer, we're told.