By Kristin Roberts NEW YORK, Feb 12 (Reuters) - Aircraft engine maker Pratt & Whitney may be close to naming express shipper FedEx Corp.(FDX)and Dubai's Emirates airlines as new customers for an engine to power the A380 superjumbo plane, according to industry sources close to the situation. The deal with government-owned Emirates could be valued at more than $500 million, said the sources, who did not put a value on the FedEx agreement. Pratt's customer win with the GP7000 engine would be a blow to rival Rolls-Royce Plc(RR), which has supplied the engines on other Emirates aircraft. Pratt, a unit of manufacturer and defense contractor United Technologies Corp.(UTX), said on Tuesday it expects to announce two new customers in March for the GP7000. The engine is being developed for the Airbus 380 plane through an alliance between Pratt and General Electric Co.'s(GE) GE Aircraft Engines. Robert Leduc, president and chief operating officer of Pratt's Large Commercial Engines segment, said the customers were "not announceable." Leduc's statement, made at the SG Cowen aerospace conference in New York, marked the second time the company mentioned the possibility of pending orders for the GP7000 engine family. Two weeks ago, United Technologies said Pratt had "significant additional customers" yet to be announced. Chief Executive George David at that time also declined to name the customers. Sources with knowledge of the contracts said both FedEx and Emirates may ask Pratt to delay the announcements beyond March. The GP7000 engine is one option for powering Airbus'(EAD) (EAD) double-decker wide-body A380, which at 555 seats will be the largest jetliner in the world when it reaches the market around 2006. Emirates has ordered 22 A380s. Shares of United Technologies closed down 70 cents, or 1 percent, at $68.40 on the New York Stock Exchange. GE shares fell 35 cents to $37.50, a decline of 0.9 percent.