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 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. Backgrid

We know why they're in Sin City ... they catching Ashlee Simpson 's show at the Venetian. It's the first night of her residency. Gallery Launch Gallery Getty

That's especially interesting ... why Eric would be there with Jessica if it's a Simpson family event, but there he was.

They announced their separation in January but they've been apart for muc

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