CLEAN : Airbus profits take off in 2014 no turbulence seen in 2015

The transcript discusses the company's financial performance, highlighting a 5% revenue increase and significant commercial success with over 1400 net orders. It emphasizes the importance of 2015 as a crucial year for breaking even after 15 years of investment in a particular aircraft. The transcript also mentions future predictions, challenges, and improvements made to the aircraft since its service inception in 2007.

What does the term 'order backlog' refer to in the context of the text?

What improvements were made to the aircraft since it went into service?