People were astonished as the new plane was unveiled in public for the first time on September 30th, 1968, 51 years ago. It was huge, bigger than any civilian aircraft they had seen. It was, of course, the Boeing 747, the first wide-body passenger plane to take to the skies. Its distinctive shape, with a bulge on top at the front, made it instantly recognizable. That bulge accommodated the upper deck, where there was a first class bar and lounge or additional seating, with the pilots at the front. Some first class passengers downstairs in the nose of the plane were (and are) ahead of the pilots upstairs.

It was designed as a successor to the highly successful Boeing 707, and to carry 50 percent more passengers over greater distances. Its most common current variant, the 747-400 can cruise at Mach 0.85 for a range of 8,350 miles.

It was very costly to build, requiring a whole new factory built from scratch, and Boeing had to borrow heavily. The company 'bet the farm' on its new plane, going deeply into debt with a banking syndicate. During the final months before production, Boeing had to go back several times for additional funds which, had they been refused, would have bankrupted the company. Its debt exceeded $2 billion, and the $1.2 billion it owed the banks set a record for all companies.

The gamble paid off. The 747 was popular with airlines for its extra passenger seats, and with passengers for its great range and low ticket costs. It was so successful that for many years Boeing enjoyed a virtual monopoly in the construction and sale of large passenger aircraft. Indeed, its market dominance was a major factor in the formation of Airbus, to give European manufacturers a foothold.

Boeing expected its giant, the first plane to be popularly called a jumbo jet, to become obsolete after it had sold 400 of them. It thought that the future lay with supersonic travel, and that others would follow the route of the Anglo-French Concorde, making subsonic passenger jets obsolete. In fact the 747 was designed to be easily converted to become a cargo carrier by removing seats and installing a front cargo door. The company expected its passenger role to give way to supersonic aircraft, but that it would have a much longer future as a cargo carrier. They overestimated the economics of supersonic travel, and underestimated the durability and popularity of their big bird. Production passed the 1,000 mark by 1993, and as of this summer, 1,554 had been sold.

It changed the world by bringing low-cost long-range travel within the budget of ordinary people. What had once been the prerogative of the well-to-do now became available to average families taking package holidays. It made holidays to Disney World in Florida accessible to ordinary British families. A private company took a big gamble and called it right, reaping the rewards of success.

Concorde was not so fortunate. Funded by the UK and French governments, only 20 were built, 6 of which were prototypes, with only 14 entering service. Because of the sonic boom, it could only pass the sound barrier over water, which limited its routes. It was a technological marvel. I flew it 5 times and found each one thrilling, but the economics were not good. Research and development had been costly, since it crossed new and untried frontiers. If the development costs were written off, BA and Air France could operate it profitably, but it became increasing costly to maintain. If further offshoots had been built, like stretched versions, the development costs could have been spread over several models, but it never happened.

When supersonic passenger travel returns, as it soon looks set to, it will be private companies and private investment taking the gamble, as it should be. Several models are nearing the test flight stage, with smaller planes travelling below Concorde's Mach 2.2, and with designs to avoid the sonic boom, looking likely to blaze the trail. Some of the early ones will be business jets, but ordinary passenger versions will follow. No doubt they will be fun to fly in, but it is unlikely that any will have the world-changing impact that Boeing's first jumbo had.