A modern 737 purchased from Boeing has an aftermarket value 10% higher than the purchase price. This is because of the current climate and the near 10-year backlog to get an airplane. These things are a long way away from being comparible to automobiles.
Goldman Sachs (do they have any credibility left) valued the airline fleet of AYR at around $26 a share roughly six or eight months ago. This is in part because of how they are depreciated. The book value is marked down while the aftermarket value could very well be higher if the plane is reasonably new.
I wouldn't worry about the value of the fleet - plus they're converting the few less efficient planes to freighter use. They seem like smart cats.