If you have read about the increasing number of flights making emergency landings due to overwhelming cabin odours, you’re somewhat familiar with it.
Cabin air is “bled” in from the engines to pressurise it, as well as for air conditioning and other systems. If the seal on the engine lubricant fails, it can drip oil into the hot engine air. The warmed oil then can be taken into the cabin, and cause “dirty sock”-like fumes. (©source) read article here
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