The film is effective, businesslike. The screen shows your typical airport hassle: long lines of people lugging things; harried ticket agents; crying children. Over this babble, a reassuring, informed voice, not too pushy:

"Each line, each delay, each layover is time lost forever, productivity which will never be used . . . There is an alternative.

The alternative flashes on the screen, sleek, clean. The word Learjet is never spoken during the film; it appears but once in the credits. But that 11-minute film, called "It's About Time," is unmistakably selling Learjets. If the recession is here, nobody has heard about it at Gates Learjet, where there is a $1 billion backlog of firm orders and where the production line will soon be stepped up from nine to 10 craft a month.

For that matter, the business of selling nice comfortable cabin-class business airplanes remains solid throughout the general aviation industry, while the small-plane single-engine market has taken a precipitous drop.

In the first quarter of this year, single-engine deliveries nationally were off 21 percent from a year earlier (although 2,538 planes were delivered); agricultural plane sales were down 30.5 percent, and multiengine piston-driven planes were down 10 percent, according to statistics from the General Aviation Manufacturers Association.

The next step up is the turboprop or jet, and here things are very solid. Turboprop deliveries in the first quarter increased 20.4 percent to 189 units; jet deliveries increases 24.1 percent to 67 units.

Part of Wichita is smiling.

Gates Learjet is unusual in this city that easily could be called the general aviation manufacturing capital of the world. The only thing Gates Learjet builds is business jets.

The other two general aviation manufacturers here -- Beech and Cessna -- offer a broader airplane line. While they are doing just fine with the tops of their lines, business is slow at the bottom.

Cessna, the second-largest Wichita employer with 13,500 workers recently fired 2,500 people and temporarily laid off another 1,500 (although most of them are now returning). Beech, with 11,000 employes, is looking at a reduction of 3 to 4 percent, perhaps as many as 500 people.

The boom in general aviation deliveries -- which increased steadily from 7,464 in 1971 to 17,811 in 1978 before dropping just slightly last year -- appears to be over, at least for a while. The General Aviation Manufacturers Association is predicting a total of 15,000 deliveries this year, which would make it the worst year since 1975.

So while the industry generally is in a bit of a down cycle, sales of turboprops and jets are going up. They aren't cheap either. Learjet's popular 35A model is going for $2.9 million, for example.

At a time when inflation is approaching 20 percent, money is expensive to borrow and fuel to run airplanes or anything else is expensive to buy, why are the cabin-class airplanes selling so well?

J. Derek Vaughan, senior vice president in the commercial jet marketing division at Cessna, put most succinctly the opinion expressed by others in this city:

"The answer has to be the exceptionally poor service the airlines are giving the businessman. (The business jet is becoming) the only way to get around."

The general aviation community has built an explanation that goes like this:

There are about 14,000 places in the United States where you can land an airplane, and only 350 of them are served by scheduled airlines. That latter number is decreasing (and had decreased from close to 600 a few years ago) because deregulation has permitted the major airlines to get out of smaller, less comfortable markets and concentrate on service among the big cities. Although commuter airlines are filling a large part of that gap, they are not filling all of it.

At the same time, many companies large and small have been scattering their manufacturing plants around the countryside, particularly in the more rural South and West where airline service was never great anyway. The only reasonable way for corporate heavy hitters to visit the various outposts in their empires is to do it on business planes.

Ed Burns, executive vice president of Beech Aircraft, said "I can fly to Montreal in a King Air (Beech's popular turboprop) faster than I can on an airline. Any time they have to make a stop, you can beat 'em."

Beech still hasn't entered the jet field. "Why should we make a 'me too' airplane?" Burns asked. Most business trips are shorter than 500 miles, he said, and turboprops are highly efficient at lower altitudes and shorter ranges even if they do fly somewhat slower than the jets.

Cessna and Lear are going head to head in the jet market. Both have successful lines; both have extensive backlogs; both are pushing to production a newer, larger model that will let the corporate passenger who is shorter than 5 feet 10 inches stand up in the airplane, an amenity that has been lacking heretofore in the small business jets.

How long can this keep up?

All three manufacturers here said they expect some softening in the business plane market in the months to come, but they haven't seen it yet.

"Historically in an election year customers have adopted a wait-and-see attitude," said James Greenwood, corporate vice president of Gates Learjet. "After the election, sales usually pick up, no matter which way the election goes."

Wichita is almost as dependent on the aviation industry as Seattle is on Boeing, and Wichita suffered the same kind of deep economic depression that Seattle did.