Emirates airlines has firmed up an option on 50 more Airbus A380 "superjumbo" aircraft, bringing to 140 the total number of orders for the giant carrier so far placed by the UAE company. Emirates had taken an option of the 50 planes at the Dubai Airshow in November and the two sides "have completed discussions and signed the firm contract," an Airbus statement said on Monday. No value for the contract was disclosed but the A380 has a list price of USD 390 million per unit, but this can vary depending on the size of the order and associated contracts for training, spare parts and maintenance. The statement quoted Emirates President Tim Clark as saying: "The A380 is our flagship aircraft. It is popular with our customers and delivers results for us in terms of operational performance. That is why we have ordered these additional 50 aircraft, to add to our A380 fleet." The double-deck aircraft can carry up to 850 passengers in its most economical configuration but normally operates with about 550 people on board. Emirates currently has 44 of the giant planes in operation and is the largest customer operating the A380 of which 122 have been delivered worldwide in the past six years.