STRAPPED in your airplane seat, thousands of feet in the air, you are as passive a diner as you're ever likely to be. While you might -- just might -- know whether you are going to get a meal, you probably don't know when -- and you certainly don't know what. (Of course, with all too many airline meals you're better off not knowing what, because the reality is bad enough without the anticipation.)

You can, however, improve your chances and, furthermore, exercise some choice in those meals, even if you aren't kosher or a vegetarian or don't have a specific medical restriction. With many airlines you can simply call up and order a meal from a menu that is read to you. American Airlines, for instance, has reuben or roast beef sandwiches, hamburgers, fresh fruit bowl, California quiche, seafood cassolette or -- the most popular -- a cold seafood platter. TWA has kosher, Moslem, Muslim, Hindu, children's, diabetics, low-calorie, low-cholesterol, low-fat, low-sodium, low-carbohydrate, low-sugar and seafood platters. Pan Am offers oriental, vegetarian, high-protein, low-sodium, low-cholesterol, lacto-vegetarian, kosher, diabetic and seafood platters, as well as one for bland diets (though, arguably, all of them do that automatically).

That's the theory, but what's the reality? We ordered seafood platters for flights on American, TWA and Pan Am, and found them as different as their routes. American very efficiently reconfirmed our meal when we checked in and, though ours was a breakfast flight, willingly issued us a seafood platter. Lucky thing. While most passengers ate steamy-looking steak with a homogenous fluff of egg or a crepe with gummy-looking cheese sauce, and a few chose the fresh and bright-looking fruit plate, we had a tomato stuffed with king crab (obviously real crab because it had a bit of shell) and four smallish but decent shrimp with a sliced egg and some salad greens. No dressing other than a coup of cocktail sauce, and no discernible seasoning, but it was a light and refreshing meal for a flight.

TWA did even better. The stewardess not only sought us out to see if we had ordered a seafood platter, but served us first -- a fine advantage to keep in mind. This was a lunch flight, and our fellow passengers were eating fried chicken nuggets drenched in barbecue sauce or a sturdy-looking omelet under hollandaise or beef stroganoff, all accompanied by "taco salad with sombrero dressing." Nothing we would look forward to, and in fact our seatmate turned it all down. Our tray, though, had seven large (admittedly tasteless) shrimp with a sliced egg prettily overlapped with slices of raw yellow squash. Celery and carrot sticks, iceberg lettuce, cocktail sauce and a little packet of Danish pumpernickel fluffed out the platter, and a large bowl of fresh pineapple cubes served as a far better dessert than the nearby cheesecakes.

Pan Am had two chances. They forgot about our meal the first time around, but apologized at the end of the trip. On a return flight we wish they had forgotten, because the seafood platter turned out to be a dried out, fishy-tasting fillet of anonymous fish topped with pale and soggy almond slices, flanked by lemony rice, waterlogged green beans, two wedges of heat-shriveled tomato and a slice of lemon. Another dish held 12 dates, as peculiar an accompaniment as we could imagine. Only slightly less strange was the addition of a roll and nine melba rounds. The best part was a dish of sliced oranges garnished with grapes and half a strawberry. Thoughtfully, in case the meal didn't totally satisfy, someone had added a half-ounce packet of dry roasted peanuts. It seemed like an airline meal designed by committee.

Next time we'll still order a seafood platter. But we'll make sure it is going to be a cold one, and hope that doesn't mean we get a still-refrigerated baked fish fillet.

IN the "where are they now?" category, we can report that if Philadelphia is alive and well it is in part because of Jean Francois Taquet, who cooked in Washington at Jean-Louis for two years after training with Fredy Girardet in Switzerland, then took over the kitchen at Philadelphia's La Truffe. We tried his handiwork at a dinner for that city's chapter of La Chaine des Rotisseurs and found his inventive spirit intact. The most interesting dish was a bowl of what might be considered a combination of earth and stars: earthy salsify and sliced black truffles sauteed with scallions to flavor a port-scented chicken broth in which belon oysters were just warmed. Shining only slightly less brilliantly were sweetbreads on a bed of radicchio, lobster with pimiento cream, salmon with the strong scents of olive oil and fennel and, to clear the palate, a sorbet of champagne and basil, very fresh and hardly sweet. That was only the first half of the meal, but the climax was a tiny warm pear tart floated in a very dark and creamy praline sauce. As much as such things can be translated onto paper, here is Taquet's recipe: JEAN FRANCOIS' TARTE CHAUDE AUX POIRES (4 servings) 4 pears, peeled For the caramel: 1/3 cup sugar 2 cups water For the pastry: 1 cup flour Dash of salt 1/4 cup sugar 1 egg 1/4 cup butter For the praline paste: 1/2 cup slivered or powdered almonds 1/2 cup sugar 2 tablespoons water For the praline sauce: 1 cup milk 2 egg yolks 1/4 cup sugar 1 tablespoon praline paste, or to taste (see above)

Combine sugar and water in a large saucepan for the caramel and stir over low heat until dissolved. Raise heat and let boil until it turns a light caramel color. Add pears and cook over very low heat, covered, for 20 minutes or until pears are tender. Store in refrigerator until pears are cold.

For pastry combine flour, salt, sugar and egg and work in butter well. Refrigerate for 2 hours.

To make praline paste, toast the almonds in a 350-degree oven for about 10 minutes, stirring frequently and making sure they do not burn. They are done when they are an even, light, toasty brown. Boil the sugar and water in a small saucepan until the sugar caramelizes and turns a light, nut brown. Immediately stir in the toasted almonds. Bring just to a boil, then pour onto a baking sheet. When cold, in about 10 minutes, break the hardened mass into pieces. Pulverize in the electric blender or pound to a coarse powder in a mortar. Use 1 tablespoon or more to taste for sauce and set rest aside for other uses.

For praline sauce, whip egg yolks with sugar and praline paste until light. Bring milk to a boil and slowly whisk it into egg yolk mixture. Return to very low heat or to a double boiler and cook, stirring, until sauce thickens enough to coat a spoon, being careful not to let it come near boiling.

Roll the dough thin and cut into four rounds, large enough to use all the dough. Slice the pears in half and each half into about 10 thin slices. Top dough with sliced pears, overlapping them in concentric circles. Bake at 350 degrees for 10 to 12 minutes or until golden.

When ready to serve, spoon praline sauce onto 4 plates and center pear tarts on the plates.

YEARS ago we wandered into Rock Creek Park and found what seemed like a mirage, a long stretch of delicious-smelling foods and a large group of picnickers who invited us to join them. Next time around we brought our own contribution. And this year you can, too. The Vegetarian Society of D.C. is holding its potluck picnic today, from 2 p.m. to dark, in Grove 9 of Rock Creek Park, and the event is free to anyone who brings a vegetarian dish (no meat, fish or poultry) for four times the number of people in his group, and the dish's recipe on a 3-by-5 card. Besides food, the picnic will include games, a fire, hot cider and baked potatoes for all. For more information call 779-8343.