Delta Airlines has announced that it's awakening more than 550 aircraft put into hibernation after demand for seats on flights plummeted in 2020 during the COVID-19 pandemic. Airlines all over the world had to park and store their fleets during the pandemic, stashing them in places ranging from the Australian outback to the Mojave Desert in California. By one count, 16,000 aircraft — about two out of three airliners in use — was in hibernation by May 2020. Storing a jet airliner for an extended period isn't the same as putting your car in the garage while you're on vacation. Hibernating the big planes requires elaborate preparation and careful periodic maintenance to keep them from deteriorating. Restoring them so that they're ready to fly again is an equally complicated task. When an airliner is parked for a while, there are a number of things that the airline has to be concerned about, including exposure to freezing temperatures or high levels of moisture. That’s one reason airlines choose to store planes on airfields in the desert, where humidity is low. That doesn’t eliminate the problems, though. Sunlight can damage the inside of the aircraft, and the numerous ports and openings can allow insects, such as wasps, to get in. For that reason, airliners that are being hibernated undergo careful preparation. Workers will cover up the windows with reflective material and tape up the ports and openings. They'll also drain the oil from the engines and replace it with a preservative oil that's designed to inhibit corrosion. Additionally, mechanics will put bags of absorbent material — called desiccant — into spaces in the engines. They'll tape up and cover the tailpipes as well. They may also spray the internal parts of the wing with a preservative. To keep the tires from developing flat spots, workers will move the planes every so often. After an airliner has been stored for a while, bringing it out of hibernation requires the same sort of care. Workers remove the preservative oil from the engines and replace it with regular oil, take off all the tape and coverings, and then check everything on the plane to make sure that it's still in working shape. Getting all that done might take about as much time — two to three weeks — as was required to hibernate the plane in the first place. There’s a lot more to it than people realize.
