U2 are are able to grow the fleet. The business is set up in a way that it can grow and it can contract fairly quickly if needs be. Right now it is growing at a steady, sustainable rate with new aircraft joining regularly. The A319s are staying longer and aren't being removed as quickly as they once were, and so the fleet is growing. However if 9/11 II happens, or another recession hits then the fleet can shrink to adapt to the market through lease returns or selling A319s. Allegiant and Volotea being just some of the destination for U2's older aircraft. Brexit could also be a trigger for contraction or slowed growth. I don't have thefigures but it's all listed somewhere on one of the annual reports.