Lufthansa is expecting its best ever summer for bookings, driven by strong demand for premium tickets, on North American routes and a booming German economy, its chief executive said on Tuesday. "Even though we are growing 15 percent, our seat load factor is going up and that's why I'm so optimistic for this summer to be a record summer," Carsten Spohr told Reuters at the Paris Airshow, signalling the company's planes are more full even though it has sharply increased the number of available seats. Lufthansa shares were up 0.8 percent at 1139 GMT, outperforming Germany's wider DAX index, which was up 0.2 percent. Spohr was speaking after Lufthansa received the Skytrax award for best European airline at the air show, toppling rival Turkish Airlines. The German carrier has been investing billions in renewing its fleet and improving its cabins as it seeks to win customers in a fiercely competitive market and achieve a coveted 5-star Skytrax rating."It's a wonderful recognition of our premium strategy which we have focused on so much over the last years. We believe it was a major step today towards 5 stars and I'm ready to come back to Skytrax at any time," he said.