In our Engine Market Commentaries we provide a build up of how many engines exist in the world. Unfortunately there does not exist a comprehensive database of engines by engine serial number, like we have for aircraft, because engines are not required to be registered with aviation authorities in the way that aircraft are. So we start with the aircraft that we know exist (Aircraft Current) and add to that aircraft that we know are on order (Aircraft Backlog), and we then compute the number of engines that should be installed on those aircraft (Engines Current), or will be when the backlog is delivered (Engines Backlog). Engines Current and Engines Backlog is a tally of all of the engines that are or will be on the wing of an aircraft.
However there are also pools of spare engines that we can’t see in our database, held by airlines, MROs, engine leasing companies, and the engine manufacturers. The column Est’d Spares is our attempt to estimate the number of such spare engines that we think exist to support the current fleet, or will be purchased to support the aircraft that are in the order backlog. We do this by applying a % factor to the fleet numbers.
The liquidity overview section also includes the estimated spare engines rolled into the total number of engines, except for the top 5 lessors table, which only shows installed engines.