Plane tickets, especially for premium class and full-fare paying passengers on international routes, could become substantially cheaper thanks to the International Air Transport Association's reform of its "fare construction" tariff rules, which came into effect on Jan. 15.

Travel agents in one country will now be allowed to issue tickets in another, taking advantage of anomalies in fares at one end of a route because of currency rates, bilateral agreements or market forces. It is now possible, for example, to buy a ticket in London to use yourself, or to send to someone else.

This facilitates "cross-border hubbing," whereby someone based, say, in London saves a ton of money by traveling to New York via Frankfurt, where the round-trip business-class fare can be up to 40 percent cheaper. And instead of buying a round-trip ticket to get to Frankfurt, the traveler can combine two one-way tickets, taking advantage of any cheaper price from Frankfurt to London. (Please don't write to say that he or she could buy two one-way tickets with a no-frills carrier - which is another story.) Thus, the entire itinerary can be written on one ticket and bought at home, with flexibility and official "interlining" between carriers.

Creative travel agents have long known how to exploit the IATA fare construction rules by saving money on full published tariffs, especially in first or business-class, through such devices as "split ticketing" (exploiting a softer currency at one end of the route, say, between London and Bangkok); so-called maximum permitted mileage rules (that allow travel up to 25 percent more miles between two points at no extra cost, or a small surcharge), or "combination ticketing" (by which one combines two or more separate round-trips, that can be taken any time within one year, on the one ticket).

The liberalization of the IATA fare construction rules has been driven by the widespread use of online booking. IATA is pushing for all tickets to be electronic by the end of 2007.

Monique Staats, an IATA spokeswoman in Geneva, says, "With so many tickets being booked and paid for on the Internet, it no longer makes sense for airfares to be based upon country of origin; because one can't say where a passenger is located. Thus we have amended the 'directional minimum check.' The purpose of this was to ensure that if a one-way fare was sold and ticketed outside your country of origin, that fare must not be less than the fare applicable in the reverse direction. The agent would have to plus-up the price to the higher amount."

By scrapping this rule (except to, from or via Japan), the price of a "split ticket" (two one-way fares), bought in your country of origin, has effectively dropped by up to 50 percent, as in the case of round-trip business-class tickets from London to places like São Paolo, Hong Kong and Bangkok.

Sometimes an airline can only reach your final destination by connecting or making a stopover in another city. Flying from Bangkok to Sydney via Singapore, for example, transfer costs under the Higher Intermediate Point rule will now be absorbed by the carriers and no longer charged to the passenger, no matter where the ticket was issued. Passengers will now pay stopover costs due to a HIP only when a stop is "voluntary" and longer than 24 hours.

Travelers will still be frustrated, in many cases, if they try to compare prices and book tickets on airline and general travel sites based in another country. Sometimes you have to punch in a local zip code to review prices and make a booking. You may not be able to pay by credit card without a local billing address, or take advantage of insurance (as several readers have pointed out).

Look for sites that reflect the new IATA rules by allowing you to book a fare from anywhere to anywhere. You no longer have to buy your tickets in the country of departure. Armed with an e-ticket you simply show up at the airport. Airlines, such as British Airways and Virgin Atlantic, allow you to print boarding cards online.