(FORTUNE Magazine) – SURE, THE ECONOMY is stumbling, causing most FORTUNE 500 CEOs to think we are in a recession or will be soon. But GNP hasn't shown a decline, so something must be keeping our heads above water. While it would take an economic Sherlock Holmes to detect many industries that are booming, some are doing well. Commercial aircraft, with its record backlogs, is the only full-fledged member of the boom club. Second-quarter shipments shot up 29% from a year earlier, to 135 planes (101 from Boeing, 34 from McDonnell Douglas). Airlines worldwide are going all-out to replace aging craft and keep up with expected growth (see Airlines). Riding the updraft are suppliers like Valley-Todeco, a Sylmar, California, division of Lamson & Sessions. Valley-Todeco makes high- strength bolts for jet engine mounts, wing flaps, and landing gear. Says President Errol Roy: ''We are having a record year, and we expect it to continue.'' He thinks airlines will eventually stretch out some orders because passenger travel is slackening, but says demand for his products should remain strong through 1991. Now avert your eyes from the heavens to businesses that burrow into the earth: Coal output this year is up 7.5% from 1989. Much of the gain stems from utilities' replenishing stockpiles consumed during last December's cold snap. The rest reflects increases in electricity demand. According to the National Coal Association, exports are also strong, mainly to Europe. Back above ground, recreational spending is hardly in the pits. For example, the Nevada Gaming Control Board reports first-half casino revenues up 14%. Beauty and barber shops are also looking good: More and more working people are going in for pampering and products. (An encouraging economic indicator? In the recessions of the early 1980s, beauty spending declined sharply.) Other industries helping the economy: -- PLASTICS RESINS. As of June, production volume of this basic material rose 8.2% from a year earlier. ''The numbers will continue strong mainly because of exports,'' says Ronald Whitfield of Charles River Associates, a Boston consulting firm. Whitfield cites demand from Asia, the low dollar that favors exporters, and the cost advantage America enjoys thanks to cheap natural gas. -- TURBINES. Westinghouse says orders have risen more than 20% in each of the past two years. Reason: Throughout the 1980s electrical utilities, pressured by state regulation and the conservation movement, expanded only a little. Now some utilities are strapped for capacity and must grow faster. Replacement demand will also be vigorous, says General Electric, which expects turbine sales to jump 50% in the next three years. -- GENERAL INDUSTRIAL EQUIPMENT. Demand for workaday gear such as pumps and compressors picked up smartly after a winter decline, lifting production volume 3.2% above last year's. At Milton Roy, a pumpmaker in St. Petersburg, Florida, chief financial officer John McNamara says demand is greatest from the water- and waste-treatment market. -- ELECTRONIC COMPONENTS. Production has risen steadily, and as of July was 4.8% higher than in 1989. Intel, the big maker of chips for personal computers, posted record second-quarter sales and profits. Demand is especially robust for the powerful 386 and 486 microprocessor chips, a spokesman says. But orders could evaporate if computer makers fall short of sales targets. -- COMPUTERS. As of August production was up 7.6% from 1989. Not great for an industry accustomed to double-digit growth, but sufficient to help buoy the economy. Growth in PCs is waning because of the economic slowdown, says Robert Charlton of Dataquest, a San Jose market research firm, but U.S. unit sales should still rise 6%. A factor that may sustain the market: a shift by users to higher-powered desktop machines. -- MEDICAL SERVICES. This perennial gainer is also up 6% after inflation from a year ago, despite corporate and government efforts to clamp down on hospital and doctor bills. -- OIL DRILLING. In the month after Iraq invaded Kuwait, the number of drilling rigs operating in the U.S. spurted from 966 to 1,039. Next year it will average 1,160, the highest level since 1985, predicts Baker Hughes, a Houston-based maker of oil field tools. The projection looks paltry compared with the 4,000 rigs operating in 1981's oil boom. But Baker Hughes marketing research manager William Lang notes that the industry has downsized since then. With oil prices at their present level, the rigs will keep working at capacity even if the rest of America slips into full recession.