Joining the jet set. (Travel).

For many CEOs and their families, it's an annual question: Go skiing in the Rockies for spring break, or bask in the sun someplace south?

Then again, some do both. That was the case this year with the CEO of a commercial real estate firm in New York. Along with his wife, their four children and a nanny, he flew first to Vail, where the family skied for a week. Then they took off for Mexico and a week of snorkeling in Cabo San Lucas.

Each time, they flew on a private jet--an eight-seat Citation X provided, along with a pilot, by Marquis Jet Partners, one of several companies now selling memberships for private-jet travel. 'Without his Marquis plan--25 flight hours a year for about $200,000--the CEO says his family never could have pulled off their lavish two-week trip.

"There's no way to get from Vail to Cabo other than maybe take a plane to Los Angeles and wait around at the airport. This way, boom--you get on, you're off," he says, noting the trip took two hours by private jet and the scenery seemed to change at once from snowy peaks to the turquoise waters of the Sea of Cortez.

As any CEO who has hopped on a corporate plane knows, traveling by private jet is a world apart from taking even a first class commercial flight. There are no snaking lines at the airport, no tedious layovers and no threats of lost luggage, to say nothing about security and reliability.

But despite its appeal, many chief executives have limited their use of private aviation to business trips. In an age of scandal, CEOs may be reluctant to use company planes for personal tips. Buying a jet, or even a fractional share of one, can run well into the millions and require a multiyear commitment. Chartering a flight with a service whose aircraft and pilots are unfamiliar to you can raise safety concerns.

Seizing on this untapped market, companies such as Sentient, Delta AirElite and Marquis are offering private-jet memberships. For a minimum of about $100,000, you can buy prepaid blocks of time on jets that seat from six to 14 people.

The response has been strong. Sentient, the Boston-area company that pioneered the concept four years ago, has more than 1,200 members. Its single-year sales increased 78 percent last year, says CEO Mark Stone. Marquis says it sold 500 memberships in 2002, its first year in business. This year, the New York-based company expects to at least double that.

"There is a greater need for efficient transportation than ever before," says Jack Olcott, president of the National Business Aviation Association in Washington, which promotes private jet use by corporations.

The jet services companies insist they've only begun to penetrate the market. "So many people who you would think would fly privately because, a) they have the wherewithal and, b) they have serious time constraints, just don't know how to do it besides opening up the Yellow Pages," says Ken Austin, executive vice president of Marquis. "And many CEOs who fly with us don't necessarily want to open the Yellow Pages and pick out an airplane. You don't do that for a doctor. You shouldn't do that for your pilot or the plane you're flying."

Delta AirElite offers a slightly different package. A Cincinnati-based subsidiary of Delta Air Lines, it sells 25-, 50- and 100-hour plans. The 25-hour memberships cost from $99,500 to $245,500. The company, which launched the service in January has a fleet of more than 300 jets, most of them owned or operated (or both) by Delta, says Cameron Gowans, director of sales and marketing. Delta AirElite doesn't release membership figures, but Gowans says it has already received more than 1,000 inquiries.

One of Marquis's selling points is that it subleases its fleet of 500 planes from NetJets, a Berkshire Hathaway company that is the top seller of fractional shares of aircraft. NetJets also provides the pilots and maintenance for the planes. Marquis sells its memberships as single-year 25-hour blocks costing from $109,900 to $299,900, depending on the size of the craft.

Sentient, formerly eBizJets, has a different model: It sells debit cards for $100,000 to $500,000. A $100,000 card can yield up to 49 hours of roundtrip flights on a small jet, such as a six-seat Beech Jet 400. Sentient charters its planes, all of them from highly reputable sources, Stone says. Both Sentient and Delta AirElite retain an independent safety-auditing firm.

It was the promise of both safety and convenience that sold the real estate CEO, who for privacy reasons declined to be identified. "What I was buying was reliability," he says.

Of course, things don't always go seamlessly. On the day his family planned to fly out of Eagle County Airport in Vail on a Saturday in late March, there was so much private-jet traffic that for awhile it appeared they would have to drive 90 minutes to Grand Junction and take off from there in a different plane. In the end, after some delay, they managed to fly out of Vail. "There is a disadvantage to flying even privately when everyone is on vacation," the CEO says with a laugh. Nothing's perfect.

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* Up to 50 hours: Jet membership or charter

* 50 to 100 hours: Jet membership or fractional share

* 100 to 300 hours: Fractional share

* 300+ hours: Whole-aircraft ownership

Source: National Business Aviation Association