As a result of the pandemic, airlines around the world grounded their planes and put them into storage. Air Canada enRoute has published a short but interesting article on the procedures for storing aircraft and the work needed to put an aircraft back into service. It's a very quick read but does touch on an issue many of us simply don't think about when it comes to airline schedules returning to normal. Bottom line, taking a plane out of long term storage is not as simple as hopping in and turning the key. Check out the article: https://enroute.aircanada.com/en/article/airplanes-in-service