The use of private business jets will triple over the next decade, driven by the introduction of relatively inexpensive "microjets," the Federal Aviation Administration predicts.

The arrival of these very light jets could make corporate planes affordable to more companies and air-taxi services at smaller airports more viable financially. (The jets cost as little as $1.5 million, compared with $2.4 million for the cheapest corporate jets.) All that means more options for fliers. But in the process, beleaguered commercial airlines could lose high-paying customers.

The first of the new jets, the Eclipse 500, is expected to be certified by the agency after a safety review and is likely to be flying this year. The FAA said last week that it expects these jets to be popular enough to drive up use of privately operated jet aircraft by more than 10 percent a year over the next 12 years. By 2017, these twin-engine aircraft are expected to log 9.6 million flight hours, up from an estimated 3 million last year, the agency added in its annual forecast of aviation activity.

The agency predicted that 100 very light jets would be operating by the end of 2006, with the number growing by 400 to 500 aircraft each year after that and reaching nearly 5,000 by 2017. The General Aviation Manufacturers Association's projections are similar; it says the industry is likely to produce 350 to 500 very light jets a year, with a maximum of perhaps 870.

"If the microjet and air-taxi phenomena are successful, it could mean great new travel choices," says Gerald Bernstein, a partner in the Velocity Group, an aviation consultancy. But not everyone accepts the FAA's predictions.