Off Piste - Ticket to glide

I am on my annual gliding holiday in the southern French Alps. It is raining. The weather is a constant problem with flying, which is why I am in France, but even here the weather can sometimes be uncooperative.

I have been flying planes for years. The first time was in 1963 when I was a 14-year-old RAF cadet. I think the pilot instructors who flew us around in two-seater trainers had been told to impress us, so more or less as soon as the plane left the ground, it was upside down, rotating through all axes, with the blue and white of the sky sliding around to be replaced by the greens and browns of the earth below.

My instructor asked if I would like to have a go, and after I had bumbled through the sky for a while he talked me through a landing. I loved the whole experience. Strapped in the cockpit, I felt as though the plane were an extension of my body, responding fluently to movements of the control column. It was utterly exhilarating to control this mechanical object, so agile in the air, and then return it to ground.

My first solo flight was two years later. It took place in an open-cockpit glider and I flew from Hendon airfield in north London, which is now an air museum. (Today you can still see the hangars where we kept the gliders in the 1960s, but these are now filled with historic aircraft.) Our gliding was restricted to a maximum height of 800ft, which is rather low, but I have to admit that even at that age I occasionally broke the rules.

Once, when gliding alone, I soared to 1,500ft in a thermal, a bubble of warm air. A thermal forms when the ground heats up and warms the air above it sufficiently for a bubble of air to separate from the ground and rise up. The tops of thermals are often marked by puffy, cauliflower-shaped cumulus clouds of the sort you see on sunny summer days. If a glider can circle tightly enough in the bubble of air, it can go up too. On that day at Hendon, I circled in a thermal rising to a height where London gradually became spread before me, from Tower Bridge in the east to Heathrow airport in the west. And 44 years later, I am still circling in thermals. Yesterday (before it started to rain) I turned circles constantly for an hour about 500ft above a ruined hilltop castle just trying to stay up - often with an equally persistent buzzard for company.

Flying with the cadets was free and I managed to do quite a lot of gliding and some flying at school. On gliding expeditions out of London, I learned to make use of "hill lift", exploiting the fact that when the wind hits a ridge, the air rises. I began to fly over more dramatic landscapes, such as Cheddar Gorge, and to stay up for an hour or more. But it all had to stop after I left school; when I was working before going to university and while I was an undergraduate, flying was simply too expensive.

I couldn't stay away for long, however. Five years later as a graduate student I started gliding again, first in Norfolk, then Scotland, Sussex, Hertfordshire and finally Oxfordshire, where I still fly.

During this time my repertoire expanded. I had learned "winch launching" at Hendon: this is when the glider is attached to a long cable stretched along a runway. The cable is reeled in, on to a rotating drum, and the glider gains forward speed to climb at a rather steep angle. At about 1,000ft, the glider is released and can fly free to find rising air. The process is rather dramatic, but it works surprisingly well. I also used to drive the winch, and remember being provided with an axe that I was supposed to use to hack through the cable if the glider failed to release. Luckily, I never had to use it.

The other launch mechanism I learned was to be "aerotowed" behind a tug plane. The glider is attached by a rope to the tug, which climbs to about 2,000ft before releasing the glider. This is a more civilised process - but even so, bobbing behind a plane in bumpy air can be quite an interesting experience.

But the most Heath Robinson-esque mechanism I used was a bungee launcher. In effect, the glider is attached to a thick elastic band, which is stretched and then released. This type of launch has to be executed from the top of a hill. It is a very gentle method, but immediately after the glider has been released, life becomes rather busy: ridge lift needs to be found straightaway. The only alternative is an immediate landing, which explains why this method of launching has almost disappeared today.

Another way of staying in the air is "wave soaring". When strong, steady airstreams hit hills or mountains, the whole atmosphere can undergo oscillations. These occur downstream of the hills and are marked by strange, elongated flying-saucer-shaped clouds. Wave flying can be very rough, but it can also take a glider very high indeed. In Scotland, I have been to 14,000ft, and in the Alps to over 20,000ft.

Flying at these heights in a glider is a mysterious, almost spiritual experience. The world and people are very distant, and here in the Alps, the outline of the grey-and-white mountains is etched against an ultramarine sky. It seems almost impossible that you will ever return to the ground and the everyday world. The cold and the use of oxygen sharpens the experience even more. For a while, you are truly suspended between heaven and earth.

As well as gliding higher, I now glide further - sometimes up to 200 miles. This seems a long way, but as glider pilots go I am rather average. Friends have flown much greater distances.

Flying gliders has some similarities with controlling a sailing boat. Like a sailor, a glider pilot must really understand the weather to be able to find rising air in thermals, ridge or wave lift. This means a glider seldom flies in straight lines but is always circling and following a crooked route, trying to find the best lift as marked by hills or rocks on the ground or clouds in the air. Flying powered aeroplanes is a quite different experience, as the engine frees you from such reliance. A powered plane is more like a motorboat than a sailing boat.

I like to fly the best gliders possible - made from white fibreglass, with long, thin, elegant wings - because they give the best performance and so the maximum chance of staying up. In contrast, I prefer to fly old, simple planes. I am not attracted to fast, modern ones, elaborate instrumentation or complex navigational aids. It may have something to do with the fact that older planes can be more difficult to handle, so every flight is more of a challenge. I also like looking outside and navigating by following roads, railway lines or rivers rather than relying on a global positioning system to show the way. I prefer the aesthetics of older aeroplanes. They look better, they sound better, and they smell better - of wood, doped fabric and leather.

I spent some years working in New York and was able to fly from a tiny grass airfield in New Jersey where my instructor used old planes, including a 1934 biplane. He also taught "bush flying": taking off and landing in unreasonably small and inappropriate places.

These older planes are rather awkward; the pilot has to do a good job in coordinating the controls, and the engines in front are large and get in the way, making it difficult to see ahead during landing. This, combined with fickle winds and restricted landing strips, makes perfection difficult to achieve. I suppose it is the striving for perfection that I like. You have to learn strange manoeuvres that are carried out close to the ground, such as landing on dog-leg runways, avoiding rocks on the airstrip by taking off or landing on one wheel, or squeezing into a space surrounded by high trees.

I always do this sort of flying with an instructor as it is rather demanding, and he or she is always happy to provide new challenges. Last winter, for example, my instructor had me taking off on skis and landing on ice and snow. You will have probably gathered by now that I don't fly in order to do something useful like going from one place to another. I fly only recreationally; that is, for the sheer joy of it.

So why is it that I like flying so much that I have always found time for it, even when busy with a day job as a research scientist? It is not because I like taking risks. There is a saying that "there are old pilots and bold pilots - but there are no old, bold pilots". I am old and most definitely not bold. Part of the reason I like to fly is for the beauty of seeing the world from the air, especially from a glider.

When gliding in the Alps, you often have to fly close to the mountainsides. The views of the trees, the rocks, the cliffs and the snow slipping past just outside the cockpit are breathtaking. Viewing everything from above is like seeing a map spread out. It helps you to make sense of the world, of how things connect, and it makes you realise how geography, for example rivers and hills, influences human activity. This is much more difficult to appreciate at ground level.

Another factor is simply trying to fly well. Although I am a competent pilot, I am not an outstanding one, and I find striving to do as well as I can very satisfying. Then there is the sheer concentration required. There are not many occasions when you can relax. Most of the time in a glider, you are trying to find a lift and calculating whether you can reach a suitable landing spot if you do not.

The concentration drives most other thoughts out of my mind. This is healthy, because much of the time I am thinking of my day job and it is good that sometimes work takes second place, especially when an Alpine cliff is rapidly approaching. With any luck, that is exactly what will be happening to me tomorrow - should the rain stop, of course.