HAMBURG, Germany (Reuters) - First-class passengers will be able to take a shower at 43,000 feet and enjoy a drink at the upstairs bar on Dubai-based airline Emirates's double-decker Airbus A380s, the airline said on Monday.

Emirates boasted at a ceremony to take delivery of the first of 58 A380s at Airbus's Hamburg plant that the plane would have two bathrooms with showers in its first-class cabins as well as a lounge for premium travellers.

But luxury has its limits, as Emirates President Tim Clark warned passengers could not spend too long relaxing under the jets of water.

"The showers are regulated through a software programme that gives people a five-minute shower, which is ample in most cases," Clark told a news conference, adding that a traffic light system would let passengers know how long they had left.

"If you're on amber and your hair's full of shampoo, you want to get moving."

The shower also complicates attempts by Emirates and Airbus to slim down the superjumbo by some 5 tonnes by 2011/2012 to cut fuel use amid soaring oil prices and increasing calls for the industry to reduce its impact on the environment.

The plane will have to take on board an additional 500 kg of water, an increase of some 25 percent.

But Clark told journalists he was looking for ways to trim weight off the aircraft, such as by reducing the amount of paper.

"At the moment we have 1.8 kg in each seat pocket. We can't be completely paperless," he said, but information associated with sales, such as Duty Free products, currently in paper form was being put onto a retail TV channel, for example.

Emirates was also looking at curtains, carpets and seat-back entertainment hardware for ways to contribute a total of 2 tonnes in weight reduction.

Airbus meanwhile aimed to slim the A380 by a further 3 tonnes, including the airframe and by re-machining components.

"With today's fuel prices, then there's a huge pressure," Airbus programmes chief Tom Williams told Reuters on the sidelines of the event.

"It's shaving. It's not like we're going to go to one section and remove all the weight. It's more a question of trying to get the thing refined and squeezing a few kilos here and there."

Progress was also being made smoothing the A380 production process but the "question is 'does the rate of improvement match the rate of ramp-up in production?' Because of course every week that goes by we see improvement but at the same time of course the production rate's going up," Williams added.

Airbus hopes to reach a maximum production rate of four A380s a month in around three years.