Historically year of build was calculated from:-
- First Flight Date
- If there is no First Flight Date, then Delivery Date
From 8th August 2019 we changed our methodology to define year of build as the year in which an aircraft was delivered, which alleviates issues when valuing aircraft having a first flight date late in one year, but delivery date early in the following year. Where there has been a gap of 12 months or more between first flight and delivery, we now default to the first flight date to determine the year of build.
For a more detailed write up on the impact and reasons behind the methodology change, please refer to this article published by Ascend by Cirium.