EMIRATES, the biggest operator of the Boeing 777, is pressing for more information about a successor aircraft before considering an order for the replacement of the US manufacturer's bestselling airliner.

"We're working closely to get to specifications we're happy with," Emirates President Tim Clark said in an interview in Paris yesterday. "That means layouts, the seats, the galleys, getting the weights right, getting the fuel burn."

Clark has said he may need as many as 275 777s for replacement and expansion, a requirement so large his airline is likely to become the so-called launch customer of the successor plane. While Emirates is more advanced in talks with Boeing than other carriers, it doesn't expect to table an order at the Paris Air Show in June, Clark said.

Boeing's 777 is the centerpiece of the planemaker's wide-body strategy, a lucrative segment of the civil aviation market that's coming under fresh attack from Airbus and its new A350, specifically the A350-1000 that's similar in size.

The Airbus model will seat 350 passengers and is promising 25 percent greater operating efficiency than the best-selling 777 variant, the 777-300ER. The successor, dubbed 777X, will have new wings and engines.