Noise Cancellation: Destructive interference, if applied correctly, can be very useful. It is very important that an airplane pilot hears what's going on around him, but engine noise presents a problem. So, pilots can use special headphones mounted with a microphone that picks up the engine noise. A component in the headphones then creates a wave that is the inverse of the wave that represents the engine noise. This wave is then played back through the headphones allowing destructive interference to produce a quieter background. Other applications for destructive interference are "quieting" rides in automobiles and passenger sections in airplanes.