Aviation Unison?

[david at piano.plus.com]

As the Airbus 320 taxid gently to the runway yesterday at Philadelphia
(flying GlasgoW-Philadelphia-San Francisco-Redding), sitting in an aisle
seat over the wings,  I could hear the beat rate between the engines slow
down and speed up as their respective revs changed slightly.  For a few
seconds, they would slow to almost unison.  Those who sing will know the
phenomenon where, listening to a singer, one feeels one's throat and body
tense in sympathy.  On that plane, my left arm (i tune left-handed) was
itching to move something with a tuning lever, to achieve unison!