The Popsicle, a Boeing 737-400 painted bright orange and white, is a fantasy come true for the harried business traveler.

Fitted with first-class seats and serving first-rate cuisine, it jets around the world to show off Connexion by Boeing, the aircraft manufacturer's proprietary in-flight wireless Internet system.

But while generous legroom and sumptuous meals will probably not become standard on commercial flights in the lifetimes of most current travelers, Wi-Fi almost certainly will.

For now, Wi-Fi remains rare, with fewer than 1 percent of commercial aircraft offering it. It is expensive to use -- $9.95 an hour on the Boeing plan. But for it to really take off, the airlines will need to make it pay.

"Do the math," said Terry Wiseman, an expert on in-flight technology. "If the technology were there just for the benefit of passengers, the numbers just wouldn't add up."

He is right. To the estimated $500,000 to $600,000 that it would cost to fit a plane with wireless technology, add the revenue lost in the two weeks that the installation would require the aircraft to remain on the ground. And the current systems are heavy, causing the planes to consume more fuel.

With demand for the service estimated at 20 percent of all passengers, Wiseman and other industry analysts say it would be impossible for airlines to squeeze a profit out of onboard Wi-Fi, at least in the early days.

But "there are other kinds of data that can be transmitted between the plane and the ground," a spokesman for Boeing, Terrance Scott, said. "It can be used for crew communications, security cameras and telemedicine. Or imagine having sensors in the engines that transmit data back to the airline and allow it to do predictive maintenance, instead of reactive maintenance."

Lufthansa, which operates about 40 wireless-enabled aircraft, is developing an application with the Charite hospital in Berlin that allows doctors to monitor a passenger's vital signs through a broadband Internet connection.

It is anyone's guess how much the airline industry could save by installing these air-to-ground communication systems. No doubt, the marketing departments at Boeing and Airbus have run their own numbers and are using them to persuade airlines to sign up for the service.

With time, Wi-Fi may well evolve into a profit maker for the airlines. But for now, it remains a rare treat, sort of like Boeing's tasty Popsicle.