One possible cause of fires in airplanes is wiring problems that involve intermittent faults, such as wires with breached insulation touching each other, having water dripping on them, or short circuits. Notable was Swissair Flight 111 in 1998 due to an arc in the wiring of IFE which ignite flammable MPET insulation. These are difficult to detect once the aircraft is on the ground. However, there are methods, such as spread-spectrum time-domain reflectometry, that can feasibly test live wires on aircraft during flight.