Why is the number of tracked aircraft in a period sometimes greater than the number of in-service aircraft for that period? (i.e. why are stored aircraft flying?)

Here is the definition of Storage used by Fleets Analyzer: Aircraft that are not in operational service and is often triggered by periods of two weeks or longer when detected. This status is also applied to aircraft that are put into a planned storage parking program (short or long term), undergoing model conversion or unplanned maintenance activity (e.g. accident repair). It can also be applied to newly delivered aircraft that are still in fit out or full completion.

1. The aircraft could have been placed into storage part way through a month/quarter/year, in this case the aircraft will have tracked hours for that month/quarter/year but will have a status of “storage” at the end of the month/quarter/year. For example, for Ryanair, the number of aircraft for which we had tracked hours and cycles during March 2022 was 286, but at the end of March (which is when the aircraft status is calculated) they only had 38 aircraft in-service. The Ryanair example is an extreme example of this “lag”, typically this lag will manifest itself by the in-service status appearing to be 1 aircraft behind the number of tracked aircraft (and would normally be corrected in the following month). To be included in the number of tracked aircraft in a period, the aircraft would need to have been in-service on the last day of the month for at least one month in the selected period.
   
   
2. Even though an aircraft has a status of storage, that does not mean it can’t be flying. Ryanair during the pandemic is another good example of this, even though most of their fleet were placed into storage, all the stored aircraft were still tracked as flying at least once a month, we believe they did this to keep pilots’ flight hours up, to keep the storage maintenance costs down, and to keep the fleet at operational readiness.