(FORTUNE Magazine) – Bob Johnson knows cable, there's no doubt about that. He started 21 years ago with nothing but borrowed money and an original idea--a cable channel for black viewers--and created one of the most valuable franchises in all of cabledom, a five-channel empire whose highly profitable Black Entertainment Television (BET) network now reaches 59 million homes, according to Nielsen. The whole thing was worth $1.2 billion two years ago when Johnson and partner John Malone took the company private. Today it would bring $2 billion, analysts say, although Johnson thinks $2.5 billion is more like it.

Now comes word that he wants to buy DC Air, a new airline that's to be spun off as part of United's $11.6 billion acquisition of US Airways. If the deal gets past the Justice Department--a big if right now--Johnson will face at least five suits from angry US Airways shareholders who think the board, on which Johnson sits, offered him a sweetheart deal.

But assuming Johnson can overcome all that, then for $141 million ("a very expensive sweetheart," Johnson says) he gets 222 coveted slots at Reagan National plus favorable lease terms on equipment, flight crews, and maintenance staff. His airline will fly to 43 cities up and down the East Coast, and as far west as Kansas City. Johnson promises he'll paint the planes red, white, and blue, of course--something "bold and striking." No BET onboard, though, since the flights will be too short for video.

But here's the problem. Johnson has tried venturing outside the cable industry before, and he's never had much success. During the 1990s he shoveled millions of dollars from BET's cable profits into a string of money-losing ventures--from cosmetics to credit cards to theme restaurants--in a misguided attempt to leverage the BET brand and create what he used to describe, hopefully, as the black Disney. Wall Street never liked that strategy. The stock languished, hence the buyback (see "Taking BET Back From the Street," in the fortune.com archive).

Back then, Johnson said he was glad to get off the quarterly earnings treadmill and regain the "unfettered right" to do as he pleased with his company. But look at his results. Cosmetics died in 1997, even before the reverse IPO. A proposed joint marketing agreement with Bell Atlantic involving beepers and cell phones never made it past the test stage. The co-branded credit card with Chevy Chase Bank disappeared once Chevy Chase sold its card business to First Union. BET Design Studio, a joint venture with New York's G-III Apparel Group, was dissolved late last year ("because it was not profitable, and the urban market was saturated with similar products" was the blunt explanation in G-III's annual report). Ambitious plans to build a BET SoundStage Casino in Las Vegas with Hilton Hotels fizzled when "we couldn't find a site that worked for us," says BET President Debra Lee. A scheme to roll out 20 theme restaurants and nightclubs across the country stalled at four; none are yet profitable. And in February the money-losing magazine division--publishers of Emerge, BET Weekend, and Heart & Soul--was absorbed by Vanguarde Media (BET is an investor), which quickly shut down two of the three titles.

Bottom line: Two years after becoming a private company again, BET looks a lot like the kind of company Wall Street always wanted it to be. There has been a "conscious decision to really focus on our core business," acknowledges Lee. That leaves room for a $35 million joint venture with Microsoft, AT&T's Liberty Digital, News Corp., and USA Networks to develop BET.com, an African-American portal. But not for buying an airline. DC Air is strictly Johnson's own deal--BET will have nothing to do with it.

"I see it as an exciting opportunity to build a successful airline business that will serve three million passengers who fly into DC National," says Johnson, "and it's one that I feel I can be successful in." We'll see if it flies.