There has been a tremendous shake-up in the charter-flight business this year, raising anew the question of whether you should travel this way. The cheap, promotional fares offered by regularly scheduled airlines have attracted a lot of vacationers, badly hurting the charter operators.

Some operators have gone out of business,others are in trouble. A good many charter flights have been canceled. Even if a disappointed customer gets his money back after a flight in scrubbed (and most do), his vacation plans are left in disarray.

By and large, charters are still cheaper for individual vacationers than the lowest-cost airline fares. But charter flights are subject to cancellation or fare increases if not enough people sign up. They often leave late at night, which you may find inconvenient. And it's not unusual to face departure delays. To avoid these risks, a good many travelers would rather pay a little more for a seat on a regularly scheduled plane.

There are many situations, however, where you might choose a charter despite the possible inconvenience. Among them:

Your destination is far away. The longer the trip, the greater the possible differential between the charter and airline fares.

You want a package trip that includes hotel as well as travel. By and large, charter operators offer cheaper trips than you could arrange yourself. The best deals on a winter vacation in the Caribbean, for example, are the combined air/land packages set up by tour operators and sold through travel agents.

You can't make the trip unless the cost is low and the price of your vacation week is pretty much established in advance.

You can't get low-cost airline seats which are provided only in limited numbers and with a variety a restrictions.

The airlines start raising the price of their lowest-cost seat - something that may well happen next year because of declining profitability. In that case, the differential between charter and lowest-cost airline fares will widen considerably.

Another popular use of charters is by "affinity groups" - people who belong to the same organization or went to the same college, and book a plane to carry their group abroad.

"Booking a charter is a calculated risk because of the possibility of delays," says Celia Goodale, executive director of the Alumnae Association of Mt. Holyoke College. "But people like to travel in a compatible group. There's a spirit there that's missing on a regular flight." The trips are cheap, she adds, "and if you book with responsible people, there's no trouble."

"I had a charter to London that was hours late on a late-night departure and swore I'd never use a charter again," says Frances White of the Alumnae Association of Smith College. "But the rest of the trip was fine. In view of the low cost, the inconvenience really didn't amount to very much." Even group fares on scheduled airlines are expensive, White found, "so I'll be doing more charters."

In short, a trade-off between price and convenience with price generally carrying the day.

Harriet Friedlander, president of travel agency, Academic Arrangements Abroad, in New York city, says the acceptability of charter very much depends on the group. Older people, for example, might be happier with fixed departures and returns on well-known airline, even at a higher price.

If your group is going to a place not normally visited by a lot of tours, charter flights may be more expensive than scheduled airlines, Friedlander says. There may be no other group readily available to book the plane's return flight so you'd have to pay the extra cost of having the plane fly empty one way.

If you do go anywhere by charter, on important tip: Make out your check to the tour operator's escrow account, not to the operator or to the travel agent. Note the flight's destination and date on the face of the check and write "for the deposit only" on the back.

Making the check out to the tour operator is a risk, because he might go out of business or misappropriate the funds. The Civil Aeronautics Board has just filed suit against two operators who failed to refund passengers' money for canceled trips. But checks made out to the escrow account can't be used except for the expenses of the trip. If refunds are necessary, the money is on tap. es. There were no serious injuries.