On budget, on time -- now it just has to work

For those of us used to the idea that British grand projects invariably go wrong, who are habituated by the Dome, the Jubilee line extension and Wembley Stadium to stories of schedules and budgets busted, Heathrow Airport's Terminal 5 is a surprise. And for those of us - that is to say almost everyone - who think of Heathrow as a man-made purgatory, a conspiracy of confusion and drabness to suck out the human spirit, Terminal 5 is also delightfully unexpected.

For here is a £4 billion project which, when the Queen opens it today, will have been completed on budget and ahead of time, without the tales of catastrophe that traditionally accompany such works - despite the wobble of yesterday's security alert. It also offers spaciousness, a sense of direction and of order, a degree of architectural dignity, clarity of layout, natural light and views to the outside - none of which has been much in evidence in the entire history of Europe's busiest but most charmless airport.

Designed by Lord Rogers's practice, Rogers Stirk Harbour and Partners, it will be architecturally ahead of most British airport buildings, although less smooth and impressive than Lord Foster's recently opened and vast Terminal 3 in Beijing. Departing passengers will pass through the huge volume formed by the Terminal's big curved roof; those arriving will enter a steep, glass-walled, canyon-like place populated by graceful and pleasingly-coloured lift towers, which will then lead to a plaza filled with mature plane trees. Light, greenery and space are simple enough pleasures but they have rarely been on offer on BAA's premises before.

Connections to public transport will be simple and direct. The full genius of the modern retail and catering industry will, with the help of an imposing array of brands, serve the tastes of almost every imaginable faction of the airport's demographic. I say this without sarcasm: while I appreciate small independent-shops as much as the next person-I am also deeply grateful for the fact that at least some big chains now know how to offer food and merchandise that people might actually want. Terminal 5 will give us both Gordon Ramsay and Krispy Kreme doughnuts, and I will be glad to see both.

Over the coming months we will have to wait and see, of course, whether or not the baggage-handling system works and security queues gum up the concourses. But now it looks as if London will have one of the best new airport terminals in the world, judged by how well it serves the needs of passengers and the quality of space that it creates. This is not a statement that can often be made. Stansted flickered, briefly, when it opened in 1991, but its elegant architecture was soon drowned in the illconsidered accretions of commercialism.

Like St Pancras International, which opened last autumn, Terminal 5 is a monument to a newly effective kind of project management. Its first principle-is to set a big enough budget early on so as to avoid stories about escalating costs and then stick to it. Others are to get lots of retail in, to set some (albeit not too ambitious) architectural standards and laboriously to ensure that everything happens as intended. The Olympics are being organised along the same lines. Were it not that the Government chose to mislead us about its true budget, the management of the Games would now be looking reasonably competent.

The managers of very large projects, haunted by spectacular recent failures, have made it their mission not to repeat them. At Terminal 5 they have succeeded, and this is progress. But - and there is a big but - success has a price. Impressive though Terminal 5 is as a feat of organisation, it has flaws and compromises that keep it from being wonderful.

It is dogged and effective rather than truly inspired. The architects' original idea was for a great roof spreading gracefully over the site, but this was compromised when the available land was reduced in the course of the Terminal's lengthy planning inquiry. The roof now perches awkwardly on a great stack of functional floors, like a cocktail umbrella on a hamburger.

The retail spaces dominate to an excessive degree: admirable though the shopping is, there are also times when you want to get away from it - which is not allowed at Terminal 5. So just when the building is about to get really exciting, something prosaic - a cut-price material or an ill-placed coffee kiosk - brings you back to earth.

To see what a really great airport is, you would have to go to Madrid's new Barajas airport, designed by the same practice of Rogers Stirk Harbour. This is a genuinely uplifting place whose roof undulates and flows with an abandon not seen at Heathrow, and whose ceiling is lined with bamboo. This unexpected but brilliant choice of material is soothing and calming, beautiful in itself, and distinguishes Barajas from every other airport in the world. The ceiling at Terminal 5 is humdrum profiled metal.

Barajas is sharply detailed and architecturally consistent. Like Terminal 5 it has plenty of shopping but it is contained. You are given more space to enjoy the experience of just being there. You are not directed down routes (as you will be at Terminal 5) that ensure you are exposed to as much retail frontage as possible on your way to your plane.

Terminal 5 was certainly not helped by the epic planning inquiry that preceded it, an exercise that sapped morale, energy and money; if some of the inquiry lawyers' fees had been spent on ceiling finishes we would have a better result. Some would say that the inquiry in turn resulted from inadequate national leadership, which failed truly to address the question of whether Heathrow was the right place for London's main airport at all.

Moreover the recent torrid times at BAA have been driven largely by fierce criticism of the queues and lost baggage at Heathrow: unless Terminal 5 can prove itself on those mundane but essential functional issues, then the new spaces and light will be lost on many passengers. We should not take this for granted. Terminal 5 has to work as well as other good-looking airports do.