If Turner flew a Tristar

I was somewhat loaded with cheeses, as one should be returning to London from Paris. And with a bunch of sweet-pink roses mingled with silver-green eucalyptus. And with a long French loaf (a ''flute'' is it?). And a Grand Palais exhibition catalog. And a memory-full of the Champs Elysees lined with tricolor banners; and of those yellow gravel promenades one uniquely associates with the very feel, underfoot, of Paris - ankle deep then in brittle autumn leaves.

The exhibition, unconventionally, had been of an English artist: Turner - that visual poet of ecstatic distances and ''aerial perspective.'' Who, comparably, has ever made sight extend itself so deeply into reaches far beyond the mere horizon? When Turner gazed across a valley his eye saw landscape as atmosphere without limits, as endlessness, as mist and light merging into ungraspable dimensions.

Having flown to France, I was perhaps still feeling a trifle airborne, but I had wondered suddenly how Turner had achieved such a bird's-eye view of the world, still so enthralling today, without benefit of British Airways. Of course , he forever traveled in search of Alpine passes, of hillsides, of elevations from which he could survey the world spread out below as if he were Zeus on Mount Olympus, but. . . .

My cheeses, roses, and I flew back to London that night, as the result of a strange chain of events, on the flight deck. The air hostess didn't need to tell me that this was a remarkable privilege and that the captain had a heart of gold , allowing two of us into his sanctum completely on his personal responsibility. For me it was the experience of a lifetime.

I was (being unmechanical) as duly impressed by the instrument panels as a troglodyte would be in a modern kitchen. But I was also surprised and pleased to note that even airline captains don't always know quite where they are going - on the ground, at least.

As we taxied forward to takeoff in our exclusive cockpit with its deep bay windows, its wide-angle outlook, a certain puzzlement was in the atmosphere.

Captain: ''It's first right, isn't it?''

First officer: ''No, second right . . . I think.''

Captain: ''What does it say on that board down there, can you see?''

First officer: ''Block 84, 2,400 meters takeoff run available.''

Captain: (to bemused jump-seat passengers, aside): ''It's a very easy place to get lost in. And it won't do if the runway is too short.''

After added consultation and study of a little map, agreement is reached: we turn third right and within minutes our giant proboscis is accelerating down a dead straight line of bright white lights, and we have liftoff.

I shan't forget that flight. As an ordinary passenger, with only a tiny porthole and a one-sided view, one misses a great deal.

It was a clear night except for occasional smudges of ground mist. Millions of city lights twinkled below us in constellatory configurations. The crew relaxed after a while and began to talk about things other than air traffic control instructions and height checks. The captain was telling a story about some relative who took a wrong train, ending up in Birmingham instead of Brighton.

''She's not very bright,'' he commented chuckling.

''Turn right here?'' hazarded the first officer, resuming curter tones for a moment.

''Turn right,'' assented the captain. And then we saw it: the channel set out below us like a narrowing river between the coastlines of France and England.

''That'll be Calais, there,'' said the first officer, ''Dover just across the strait . . . and that wide orange glow, see, straight ahead in the distance: London.''

London! The lights of London visible even before we'd left France! Only Turner could have painted that: ''Londres vu de Boulogne.'' A spontaneously shrunk Europe! I was reduced to a rather silly state of awe and amazement.

But even the crew, surely immune to such things by now, seemed almost schoolboyish as they pointed out various urban galaxies in the darkness extending under us: Hastings . . . Eastbourne. . . .

''Those lights to the right,'' said the captain, ''will be Tunbridge Wells, I think - yes - and Horsham to our left now.''

The universe seemed turned on its head: Instead of gazing up at a charted sky with Cassiopeia and Ursa Minor and the Plow, here was England below like a spangled network of star groups, floating in the blackness, with names like Guildford and Dorking and Maidenhead. It seemed odd that the crescent moon, suddenly in view to our left, shared the sky with us, and wasn't down there among the dancing spider's web of stars called Basingstoke. . . . And then London gradually filled the whole extent of our view, a great, wide ocean of lights.

Oh, Turner! You were born about 150 years too soon. Surely your vast, expansive art was made for air flight. But, then, a hop in a Tristar from Paris to London would have been hardly enough for an ambition as thirsty as yours: You would have had yourself lashed to the mast of a moon rocket feeling ''bound to record'' what you saw.