Answer:
Propellers or jet wings further cool the supercooled water droplets, causing precipitation.
Step-by-step explanation:
Altocumulus clouds are composed of supercooled droplets, which means they are at sub-freezing temperatures. There are areas of low pressure around the propellers or over the jet wings, which can cool the air to well below the original temperature of the cloud layer, forming ice crystals, which then fall towards the ground i.e precipitation. A hole is then found in the area from where the precipitation occurred.