PAUL JACKSON has strong opinions. With a successful career spanning air and surface freight transportation, air and surface freight forwarding, co- authorship of a book on air cargo distribution and publishing, his professional credentials form a substantial underpinning for the activities of the Triangle Group. He is chairman.

We are dining in a Knightsbridge restaurant, and Mr. Jackson is ebullient about the international acceptance of Triangle's ambitious World Express Conference and Exhibition, the third of which will be held in New York in May. He recalls our earlier talks - our friendship goes back some two decades during which we have remained in fairly regular contact - and declares in a triumphant voice that "It's finally happening."He had been a proponent of the total cost concept and its application to air freight distribution - an economic principle that I shared - and thought the airline industry fumbled it and eventually all but abandoned it as a marketing tool. Mr. Jackson, however, never lost faith in TCC's worth.

Now, he holds, TCC is raising its battered head again. This time it's ''the express industry that's making it valid." And given the traditional air carriers' concern about the express industry's inroads in the air cargo business, it is hardly extravagant to anticipate the airlines' rediscovery of TCC.

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TRIANGLE'S YOUNG CHAIRMAN - he is still in his 40s - started his career with British Airways and cut his teeth on hard freight, and presumably has the depth of experience to make well-founded judgments. He maintains that "the air cargo industry is a better one today because the express carriers made it better." He credits them with having established new service standards and, by example, "forcing the others to improve."

Citing Federal Express' purchase of Flying Tigers, the world's biggest all-cargo airline, Mr. Jackson says that transaction sent a tidal wave of shock through airline industry boardrooms. But the merger also went well beyond the first shock, he holds. It shook up airline corporate managements so that for the first time they began taking a closer look at the current record and profit potential of cargo departments. Only a small handful of international air carriers are regarded as "serious" participants in the cargo field.

Asked for his thoughts on the new era that will open in Western Europe with the lifting of international trade barriers in 1992, he hews to the conventional view that despite an expected increase in flights and cargo capacity, "intra-European trucking will benefit most" due to the short distances between markets. But he also predicts that "the express carriers will have a lot more to gain than the airlines."

Mr. Jackson regards air cargo as one industry, even though its components are segmented. Thus it is not surprising to hear him define express as "high- quality freight." He predicts that ultimately the distinction between express and freight will vanish because of irrelevance. A new term will materialize - express freight.

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ALTHOUGH IT IS ARGUABLE that this phrase will come into common usage, there is no room for disagreement that it accurately reflects what air cargo is all about.

An air shipment, whether an envelope, small parcel, crated tiger, lashed machine or igloo container, was always cargo moved under expedited conditions, especially in comparison to surface transport.

The decision to fly an item, regardless of its size, was made because the shipper understood it was the inherent nature of the service to telescope time. So there is logic in Mr. Jackson's projected term, in the sense that it denotes the ultimate in air cargo service. In any case, as Triangle's top officer sees it, the air cargo industry is moving toward express becoming the standard vehicle for all customers demanding quality movement.

Does the reversal in freighter interest, signified by the upsurge in airline investment in all-cargo equipment, presage a comeback? Paul Jackson doesn't see it this way. The only way the freighter can be restored to its former glory will be if and when all-cargo airports, served by road-feeder networks, are developed. And to this argument, Mr. Jackson asserts that this plan can justify itself only when part of a low-cost system.