The American aviation authority has told airlines not to allow the fuel tanks of Boeing 747 jumbo jets to run dry - because of the possibility of an explosion.

Some industry commentators say the ruling will cause longer journeys, cost airlines money and raise journey times and prices for passengers.

But British Airways, which uses 40 of the planes for long-haul journeys, says passengers will hardly notice the difference.

British Airways communications manager Peter Middleton explained the weight may be reduced on some of the long haul flights in and out of the UK.

But he was confident there would be no disruption to services.

He went on: "The number of seats in some flights might have to be reduced but those reductions are already close to matching the loads we are currently carrying."

Virgin Atlantic says that it will be unaffected because it uses Airbus planes for long-haul journeys.

At the Paris Airshow in June 1995 an aircraft was hailed for flying "around the world with only one stop" - so when travel routes rarely travel this kind of distance, what is all the fuss about?

Long-haul work-horse

There are currently 1,087 747s in operation, of which 247 are registered in the USA - where the FAA has jurisdiction.

The Boeing 747 faces competition from the Airbus 340

The emergency order comes after the FAA found a problem with the 747-400s. This is the latest series of the 747, and the only one still being made.

The ruling says the central fuel tank must not be run down very low. There must be a minimum of 3,000lbs of fuel in the tank.

The ruling also says that fuel tanks in the tail, only present in the 400 series, must not be used at all. And so it is only the 747-400 performance that will be affected - and only on the longest journeys.

With a load of 420 passengers (it can carry up to 568) the 747 can travel 8,200 miles.

Most long-haul journeys are split into two stages and so the range of 8,200 miles is enough for the first stage.

Consumption on the up

The key question is one of fuel consumption.

Heading into a strong westerly wind, for example from Bangkok to London, uses up much more fuel than flying with the wind behind. Consumption also depends on the load and the type and size of engine.

But a 747 can hold up to 382,611lbs of fuel and uses around 22,500lbs an hour, so generally could fly for around 16 hours non-stop.

A BA flight from Kuala Lumpur to London, which usually takes about 11-and-a-half hours, will not be able to use its tail tank and will have to retain a minimum of 3,000lbs in the central tank.

With these fuel restrictions it will have to stop off somewhere in Europe to take on more fuel.

Passing on the cost

Peter Jackson, editor of Jane's The World's Aircraft, told News Online the cost implications could be serious.

"The thing to remember is that when passenger planes are sitting on the tarmac, they're not in the air making money," he said.

"Not only will planes have to pay extra landing fees to refuel, but there is also the cost of fuel used to descend, circle, land and then - loaded with fuel - use full throttle to get back into the skies."

There is also the question of added time. Longer journeys may affect catering and passenger comfort as well as the possibility that connections could be missed.

So although the airline industry is playing down the effect of the FAA ruling for passengers, it remains to be seen who will pick up the cost on these flights.