(FORTUNE Magazine) – Anyone prone to airsickness might resist a ride on airline stocks. They have already climbed 40% this year. Meanwhile, it's by no means certain that the sunny skies of healthy profits are here to stay. After hoisting fares, some airlines have had to resort to Kids-Fly-Free programs, $76-to-anywhere tickets, and other aerial equivalents of all-you-can-eat. John Pincavage, a partner in the Transportation Group investment banking firm, is bearish. He points out that debt levels are heavy, labor costs are rising, and the costs of rejuvenating those creaky fleets are sobering. Others wonder how the carriers will navigate the next recession. So why are investors piling on board? Because they don't want to miss the exciting in-flight movie: Takeover '89. Alfred Checchi's June deal to acquire NWA showed that huge debt is no deterrent to raiders, who can squeeze a lot of cash from the assets through such methods as selling planes and leasing them back. And the survivors of deregulation are in fairly good shape to withstand a cyclical downturn. UAL is the most frequently mentioned takeover bait. A highly regarded management has already paid down a third of its restructuring debt, and earnings have improved steadily for the past 18 months. The company has $1 billion in cash, owns a high 85% of its planes, and has potential for growth on its Pacific routes. The stock jumped to $166 when the pilot's union said it might revive its bid, but analysts think that UAL could fetch $300 a share. Delta Air Lines and AMR are also mentioned as possible targets these days, with takeover values for each estimated at around $100 per share. Says analyst Kevin Murphy of Morgan Stanley: ''Even without a takeover, these stocks have great possibilities.'' Both carriers have good profits and balance sheets, and both have benefited from the Eastern Air Lines strike. The mere prospect that one of the industry's giant birds might succumb to a takeover would put a lot of sparrows in play. Says Charles LaLoggia, editor of LaLoggia's Special Situations Report, an investment newsletter: ''If some of the large airlines like UAL, AMR, and Delta begin to fear a takeover threat, they may look to acquire another carrier as a defensive move.'' High on LaLoggia's short list of lesser-known takeover plays is Alaska Air Group, a fast-growing, well-managed regional airline with routes stretching from the Arctic to the balmy Mexican resort of Mazatlan. A convertible offering in June threw some icy water on the stock, which rumors had already heated up to $30 a share. Estimated takeover value: about $40 to $45 a share. LaLoggia also likes Metro Airlines, which operates a number of commuter lines. AMR's American Airlines, which has taken over five American Eagle feeder lines over the past year and a half, may buy the two owned by Metro -- or Metro itself. LaLoggia thinks Metro's Eagle operations alone are worth between $8.60 and $10.75 a share. ''That's more than the valuation the stock market is placing on the entire company,'' he says, ''and you get Metro's Eastern and TWA feeder operations for free.'' Because of the long strike and bankruptcy at Eastern, Metro's stock has languished at around $7 a share.

CHART: NOT AVAILABLE CREDIT: NO CREDIT CAPTION: SOME OF THESE CARRIERS MAY GET CARRIED AWAY With both takeovers and recession in many crystal balls, shares of these airlines could reach the sky -- or get put on standby. That's a Delta jet being loaded in Atlanta.