(MONEY Magazine) – With a record 455 million people flying last year -- nearly double the number just a decade ago -- you might think that U.S. airlines would be reaping windfall profits. They're not, and that's the reason for the recent turbulence in air fares that is frustrating price-conscious travelers. To put matters in perspective, flying remains a bargain. Even with recent increases, fares average 25% lower, after inflation, than they were before 1978 deregulation. And 91% of passengers still buy discounted tickets that save them an average of 60% off the full coach fare. Nevertheless, with airlines under pressure to punch up profits and skies perhaps a little too friendly now that eight carriers dominate 90% of domestic travel, the cost of flying is trending skyward. In fact, 1988 marked the first year in the past eight when air fares (which rose about 7%) outpaced inflation (about 4%). Part of the increase came from ''yield management,'' a technique under which airline computers change fares more than 200,000 times daily to maximize revenue. As a result, booking has become a cruel lottery in which you must strive to avoid being the one person in 10 who gets stuck paying full price. So whether you are making a day's business jaunt to Pittsburgh or planning the European tour of a lifetime, here are tips to help you avoid getting taken for a ride: -- Check for split-ticket bargains. For example, it's $206 cheaper to fly Delta from Dallas to Albuquerque ($84) and then Albuquerque to Los Angeles ($58) than to book a $348 full-fare flight from Dallas to L.A. The reason is that Delta competes with Southwest and America West in Albuquerque. Other cities with split-ticket breaks: Phoenix and Las Vegas. -- Consider the ''nested maxsaver'' strategy. Suppose you are facing a quick hop from New York to L.A. at the full-fare price of $1,176 round trip. You can fight back by purchasing two pairs of discounted round-trip tickets that include Saturday night stays and cost only $358 each ($716 total). The first might take you from New York to L.A. on Feb. 7 with a return on Feb. 16; the second would be from L.A. to New York on Feb. 9 and back to L.A. on Feb. 14. Using only the first half of each round-trip ticket, you'd go out Feb. 7, come back Feb. 9 and still save $460. And the second half of each ticket could take you back to L.A. -- out on the 14th, back on the 16th -- for free. -- Look for ''hidden city'' routes. This time you are flying from Salt Lake City to New York and a one-way coach fare costs $515. But you buy Pan Am's M fare from Salt Lake City to Washington, D.C. via New York's John F. Kennedy airport and save $326 simply by getting off the plane at JFK. The carriers don't like this, of course, and are trying to close these loopholes. But as the table opposite shows, hidden cities still abound, especially at airline hubs. If you don't want to sniff them out yourself, check the monthly listings in Best Fares (800-635-3033; $68 a year). Two cautions: use the ploy only one way, since the airline will cancel your return ticket if it catches you. And don't check any bags -- they'll wind up in D.C. -- Establish an ongoing relationship with a travel agent. Some 63% of fliers book through an agent, according to the latest MONEY/ABC poll -- vs. 34% who call airlines directly -- but not all use the same agent trip after trip. Finding bargains takes work, so you get your best service from one who is eager for more business. -- Book early. The deepest discounts require 7, 14 or 30 days' notice. And fly off-season: January and February for lowest rates overall; Easter until Thanksgiving for warm-weather destinations; November through March for Europe. -- Ask whether your agent accepts commission overrides. These are fees or special considerations -- such as free travel -- that airlines give to travel agents over and above their normal commission. Most agents insist that they never sway a customer to a particular airline just to gain favors. ''But if you want your agent to be a totally unbiased professional,'' advises Ed Perkins, editor of Consumer Reports Travel Letter, ''naturally it can matter.'' -- Ask which computerized reservation system your travel agent uses. All five big ones are owned by airlines (the Sabre system by American, Apollo principally by United, Pars by TWA and Northwest, SystemOne by Texas Air and Datas II by Delta). Both the General Accounting Office and Department of Transportation have complained that agents using these systems may tend to favor the owner airlines. If your travel agent uses Sabre, and you always wind up on American, get a competing price quote next time. -- Double-check your agent by calling an airline or two. Often carriers don't release discounted seats to a competitor's computer, so a follow-up call may unearth bargains. -- If your travel plans are flexible, stress that. You'll have to give a rough idea of when you want to fly, but don't get pinned to a precise day or time. Instead, ask the agent to call up the fare-finder screen, spot any discounts and explain them to you. Try flying to an alternative airport (Midway instead of O'Hare in Chicago, for example). Or change planes. ''Try to make your travel plans fit the lowest fare, not the other way around,'' says Joe Broesler, manager of international rates at Hickory Travel Systems in Saddle Brook, N.J. -- Fly home Sunday. Since the best deals often require you to stay a Saturday night, some travelers find it cheaper to book a hotel room for the extra day or two. -- Book the cheapest seat available but keep calling back. New discounts can crop up at any time. Or reserve a cheap but unrestricted fare (one with no penalty for a change in plans) for another day and head to the airport on the day you really want to fly. Chances are you will find a vacant seat, since planes average only 60% full. -- Ask about discounts. US Air gives anyone over 65 a 10% price break; Continental slices unrestricted fares 20% for children between the ages of two and 11. -- For overseas flights, seek out an agent with an international rate desk that can find discounts on multistop trips. Example: a traveler going from New York to Stockholm to Vienna to Innsbruck to New York would pay $1,444 full fare. But by booking an Apex ticket to Vienna with a stopover in Stockholm and a return from Innsbruck, plus a one-way fare from Vienna to Innsbruck, VTS Travel in New York would save him $658. -- If traveling full fare to Hong Kong, Bangkok, Pakistan, Eastern Europe or someplace else where the dollar is strong, buy the return fare in the foreign currency. -- Ask your agent to book through a reputable consolidator. These are brokers who buy and resell tickets for 5% to 30% off. Expect to fly an off-brand airline, though. Above all, be persistent. Today's fare structure is so byzantine that even experienced travel agents have trouble navigating it. ''The bottom line,'' says airline analyst Edward Starkman of Paine Webber, ''is that people will have to shop around and stay better informed.''

CHART: NOT AVAILABLE CREDIT: TABLE: WARREN ISENSEE CAPTION: Seek and ye shall fly: The hidden-city ploy Since business travelers who must book flights at the last minute often get stuck paying full fare these days, some of them have begun exploiting quirks of the airlines' complicated fare system in order to save money. One such trick is to fly a so-called hidden-city route. You reserve a discounted flight to a point beyond your destination that happens to make a stop at your destination, and simply get off the plane at the connecting airport. Airlines say this is against their rules and have tried to eliminate such price breaks. But as of early January, more than a dozen still existed -- including the six shown below.