12 Israeli pilots flying six aircraft 422 meters below sea level have set a new Guinness World Record for a low formation flight. The record setting flight is unlikely ever to be broken, due to the unusually difficult conditions that go along with flying at low altitudes over the Dead Sea.
http://www.algemeiner.com/2014/01/20/israeli-pilots-break-guinness-world-record-flying-low-over-dead-sea-video/