Though it seems much longer, it was only five years ago, on May 24, that airline passengers began flying at twice the speed of sound to and from the United States in the world's first supersonic commercial plane, the Concorde. Since that spring day in 1976 when the Concorde first carried paying passengers in regularly scheduled service, well over three-quarters of a million people have flown supersonically -- twice as fast as the regular subsonic jet and nearly 12 miles above the earth.

Despite various opponents' dire prophesies, all the passengers have lived happily to tell of their thrilling experience. In five years of day-in, day-out flying, the Concorde, at this writing, has not had a single accident in the air or on the ground and has not injured a single passenger or crew member. Nor have its excursions into the stratosphere caused any reported passenger illness from overexposure to cosmic rays.

After several flights were delayed in the first few months because of minor mechanical and engine trouble, Concorde settled down, worked out the bugs and now is completing 95 per cent of all scheduled flights on time.

In aviation circles, this is considered an amazing record for a new airplane, especially for one that blazed so many difficult new trails in design and engineering in both its air frame (fuselage, wings, tail assembly) and engines. It was also unexpected because the plane was researched, developed and built by an international consortium consisting of the French government and its aviation industry, Aerospatiale, in Toulouse, and the British government and British Aircraft Corporation, Ltd., with plants at Filton near Bristol in southeastern England.

Also unexpected, certainly by most competing airlines (none of which has a supersonic airplane) has been the acceptance (primarily by a group of affluent and expense-account travelers) and popularity of supersonic flight (so popular that it is frequently difficult to book a Concorde seat between New York and London).

British Airways reports it has carried close to 600,000 passengers to date; Air France about 300,000. New York-London is the most popular route, and British Airways reports it is operationally profitable. New York-Paris trails, and Paris-Washington traffic has not developed sufficiently to turn a profit. Air France has just begun Concorde service between Mexico City and Paris, via New York, replacing similar service via Washington.

Critics outside the industry, and even some realistic airline officials, point to the Concorde's limited capacity -- 100 passenger seats and small cargo space -- and the fact that with present exorbitant jet fuel costs and the Concorde's high fuel consumption, it must carry between 66 and 70 fare-paying passengers on each flight just to break even. The British House of Commons' Committee on Industry and Trade recently called the British government's predictions for the Concorde overly optimistic and suggested an inquiry into current and future spending on the plane. The committee also urged that the plane be scrapped unless expenditures are cut drastically. Even allowing for politics, the questions raised are serious.

To be fair, Concorde never has pretended to be an economy-class service, and its designers were not anticipating inflationary problems and a worldwide fuel crunch. Its fares started out at a 20 percent premium above regular airlines' first-class rates and have maintained that ratio. Supersonic flight is currently for travelers whose time is so valuable that they, or their corporations or governments can pay the freight; and for executives who cannot afford jet lag from subsonic flying.

The cost of a round-trip ticket from New York to London on Concorde is $3,355, while first class on regular airlines is $2,860 -- a difference of $495 round-trip, or $247.50 one-way. (In order to promote Concorde service from Washington, British Airways has set a lower roundtrip supersonic fare of $3,120 from D.C. to London, an increase of only $98 over regular first-class service.) The round-trip fare from Paris to New York on Concorde is $3,302 versus $2,742 regular first class -- a difference of $536. While both British Airways and Air France give their Concorde passengers lavish treatment, they really serve them no more champagne and caviar than the first class passengers on a 747, because, traveling supersonically, they have much less time to wallow in such luxuries.

The French and British governments have been involved with the Concorde since its conception. The plane was originally conceived as a joint European venture to capture leadership of the commercial aeronautics industry from America, whose airplane manufacturers are the principal suppliers of the world's passenger aircrafts. It was no political secret that the Concorde was to be a symbol of a European scientific and industrial renaissance.

However, the research and development costs ran far ahead of estimates, and to avoid bankrupting their national airlines, the two governments finally picked up most of the $3.1-billion development cost. This was not pure charity -- research work on the Concorde produced great advances in the use of industrial techniques, such as the use of laser beams as cutting tools and for fastening metal.

The Concorde's cost overruns also frightened the U.S. Congress, which was simultaneously considering financing an American supersonic plane, one already advanced beyond mock-up stage at Boeing's Seattle plant, where some parts had already been cut into metal. Congress cancelled government support, and the American project died temporarily.

With the successful flights of the Concorde, however, research and development work is already underway in the United States on new engines and supersonic airframes for a much larger plane, able to carry many more passengers and much more cargo, but flying no faster than the Concorde. This second-generation supersonic, still years and billions of dollars away from flying, may be ready when Concorde reaches the end of its normal life expectancy in 15 or 20 years.

What the cost of the second-generation supersonic will be in the 1990s is, at best, a wild guess. The seven Concordes that British Airways and Air France each bought were originally priced at $60 million apiece, including a supply of spare parts. In today's dollars the cost might run close to $100 million per plane. This compares to $50-$60 million for a Boeing 747, the largest and fastest of the commercial subsonic planes, which carries 400 passengers at 550 to 600 miles an hour.

There are actually three anniversaries of commercial supersonic flight this year. On Jan. 21, 1976, British Airways started flying its Concordes from London to Bahrain and on to Singapore. (Both routes have since been cancelled.) That same day, Air France sent its first Concordes across the South Atlantic from Paris to Caracas, and on another route via a fuel stop at Dakar to Rio de Janeiro.

Organized and vocal opposition claiming damage to the stratosphere's ozone supply from high-altitude engine exhausts, and damage to the eardrums of airport neighbors, delayed Concorde service from London and Paris to Washington via Dulles International Airport until May 5, 1976. New York did not accept the Concorde until Nov. 22, 1976.

Backers of the Concorde had faith not only in its economic feasibility but also in its safety. A long scientific study by the Federal Aviation Administration established that the combined supersonic plane flights into the stratosphere might affect supply of ozone by plus-or-minus 2 percent, an insignificant amount either way. This ended the claim that the incidence of skin cancer would increase due to the destruction of the ozone by jet exhausts. This ozone layer acts as a shield against overdoses of the sun's ultraviolet rays. Subsequent studies seem to indicate that the quantity of ozone has recently increased, possibly for reasons having nothing to do with the Concorde.

The FAA's noise abatement officers dismiss complaints about the terrible noise problem simply by reporting, as did the officer at Kennedy Airport (the original hotbed of noise opposition), that the number of noise complaints about Concorde are now so few that they are no longer a problem. I live 20 miles northeast of Kennedy, less than three minutes by air from touchdown when Concordes are landing on runway 22, the instrument landing strip. We would rather have the deep, fairly mellow roar of Concorde 1,500 or so feet overhead than the screaming banshees of the old Douglas DC-9 twin-engine jet and the four noisy engines of the even older Boeing 707.

Tests have established that at supersonic-flight altitudes -- 60,000-to-70,000 feet -- passengers receive twice as much exposure to cosmic rays as they do when flying at the 30,000-to-40,000 altitudes of subsonic planes. But because the Concorde flies twice as fast, crossing the Atlantic in 3 1/2 hours (as opposed to the 747's seven hours), its passengers are exposed only half the time and thus absorb about the same amount of cosmic radiation as subsonic passenters, an amount that has been determined to be too little to harm any human.

Flying 12 miles up at twice the speed of sound has an exhilarating, rather than a deleterious, effect upon Concorde passengers. Not that sitting as a passenger in this supersonic plane is much difference from riding in a subsonic jet. The twin seats on both sides of the singles aisle are like those in first class in a narrow-body plane; cabin space is more constricted than in the big wide-body planes, but not claustrophobic.

The exhilaration comes from the quickness with which an otherwise long, tedious flight is completed, the abrupt change from New World to Old, and vice versa, and from the dramatic reduction in jet lag suffered by Concorde passengers compared with those who fly subsonically. Judging from my own experience on two Atlantic crossings in Concorde, my jet lag was reduced at least 60 percent eastbound, probably more coming home.

That is why so many business are repeat customers on Concorde. They can start work in Europe at the crack of dawn next morning, bright-eyed and clear-headed, while arrivals in the United States on early morning flights hit the ground running for a full day's work in New York. That's also why British Airways can fill two Concorde flights a day round-trip between New York and London seven days a week and Air France is scheduling 11 Concorde round-trips this summer between Paris and New York.

A cult of Concorde aficionados has grown among nonflying fans of the supersonic, especially in some of the pubs around London. The steady customers of one pub, which was and is the local (the friendly, neighborhood, regular nightly oasis) of a Concorde pilot on his days off, spontaneously organized the first charter flight to nowhere. For 224 British pounds (about $500 depending upon the variable strength of the U.S. dollar) they all climbed aboard a Concorde at Heathrow Airport, had a nice 2 1/2-hour supersonic ride high over the Bay of Biscay, plenty of high-class food and drink, and were back home in time to have at least one more pint in their local before the 10 p.m. call of "Time, Gentlemen."