PARIS, Dec 20 (Reuters) - European plane maker Airbus SAS (EAD) (BA) said on Thursday that German airline Lufthansa (LHAG) had signed, as expected, a contract to purchase 15 of its A380 superjumbo aircraft. On December 6, Lufthansa announced it planned to order the aircraft, having agreed on a contract with Airbus that allowed it to make the purchase in spite of the industry crisis sparked by the September attacks in the United States. Deliveries are expected to begin in 2007.