Blue note (aviation)

In the context of aviation, a blue note is the distinctive whine produced by some jets, over and above the sound of their engines and airframe noise.

Considered by some aircraft aficionados as an attractive aural signature of military jets of a particular era, blue notes are often associated with turbojet powered military aircraft from the 1950s and '60s, such as the Gloster Meteor and Hawker Hunter.

The jet blue note was used as a sound effect in many of Gerry Anderson's productions.

More recently, the Eurofighter Typhoon has been cited by some observers as creating a distinctive blue note audible by observers as it flies overhead; the phenomenon is thought to be attributed to its large air intakes.In the case of the Hunter, its blue note is purportedly produced by interference drag produced by its gun ports, situated under the nose.