From the grind and pop of retracting landing gear after takeoff, to the incessant whoosh of air conditioning mid-flight, to the hydraulic moan of wing flaps extended before landing, it's clear that much goes on unseen beneath the floorboards, above the ceiling panels, and elsewhere in the guts of a modern passenger jet. In this interactive, look beneath the skin of a late-model Boeing 737, the most widely flown commercial jetliner of all time, and explore a cutaway detailing the 12 major systems that make it tick.