Anyone who's flown Concorde (and I have clocked up a fair number of trips since the late 70s) will tell you it is a remarkable experience, but also a slightly disappointing one.

For one thing, no-one ever mentions the noise: it is almost as noisy inside as out.

The roar of the engines on reheat is sufficient to make it necessary to raise your voice when talking to your neighbour and is reminiscent of travelling in a tube train.

The superjet's engines create plenty of noise

So too is the lack of elbow room. Concorde seats may cost twice as much as a first-class subsonic jet, but they certainly do not provide anything like as much room.

And if the windows look small from the outside, you should see them on the inside.

They are triple-glazed, and the inner window (if you happen to have window seat, and if you are seated far enough forward to see something other than wing) is about the size of a playing card.

A supersonic future

There is no in-flight movie system and if you need to go to the loo while the trollies are in the aisle, it means someone has to stand on somebody's feet in order to squeeze past.

So what would a Concorde successor have to provide?

The airlines have a very clear picture: a plane carrying at least 250 passengers in first-class comfort, at the same speed as Concorde (mach 2 or about 1300 mph at 60,000ft), but with twice the range - at least 5000 nautical miles.

Why those figures? Well, 250 passengers is a manageable payload and more cost-effective.

The speed is the same because above mach 2 heating problems involve having to use much more sophisticated technology.

Concorde's profile is easily recognisable

And a 5000nm range because that is what you need for trans-Pacific and longer transatlantic routes.

But wanting is one thing; getting is another.

Before anyone builds a new supersonic transport (SST) they need to be sure that it is wanted.

Not every airline is convinced. Only 14 Concordes were produced and only 13 are in use (one was permanently withdrawn by Air France).

Given all the technical and political problems it would involve, does it really make sense to build a successor to Concorde?

Little used

There are those who argue that it would be better to look at newer technology and go for a space plane - something which flies into low-space orbit, and which could (for example) make the London-Sydney non-stop journey in barely two hours.

The problem with that idea is weightlessness - people who've been into space have found floating around a cabin acutely uncomfortable, and so far no-one's come up with a solution.

Whatever the anwer, it is likely these are questions we will still be asking in 10 years.

Concorde is used so little that it does not need an immediate replacement.