History of the phrase; Prior to electronic counter measures, military aircraft would fly beneath the Radio Detection and Ranging (RADAR) in order not to be detected by enemy forces. This term started out as a military phrase in the 1950's.

Pop-Culture definition; generally an insult or can be used as advice.
1. To not stand-out, to remain quite.
2. To not drawn any attention to yourself either positively or negatively.
By not standing out or gaining any positive or negative attention, the person 'flying under the radar'
3. To go undetected.
Michael has never gotten in any trouble nor ever receive any special recognition, in fact he is disliked by his peers, hated by his subordinates; managers/supervisors have only disdain for him because he spent his 20 year career flying under the radar.

John "Dude, They will soon be on to you!"
Eric "What should I do!?"
John "All you need to do is Fly under the radar for the next two weeks"
Eric "Thanks, I will do.."
by Anon-in-il-again August 12, 2008
To act sneaky and secretly without other peoples know about it. To act furtively.
Guy 1 - Have you seen those news about the mobsters of L.A.?
Guy 2 - Oh yes, I have. They were finally discovered, working undergrounds.
Guy 1 - Haha, they were flying under the radar of our city police, but sooner or later they would be found.
Guy 2 - To fly under the radar is no easy deal, here in L.A. ... One hour or other they catch you.
by linkc007 August 1, 2016
When your about to have sex with a woman doggy style and the woman has a fat ass. To reach the pussy you must lift up her butt cheeks and fly under the radar to have sex. This can also happen when a woman have a f.u.p.a and you have to lift the f.u.p.a up to reach her pussy.
Greg: Dude your girlfriend has a fat ass! What is that like when you bang her from behind?
Jack: Well I have to Fly Under the Radar to reach her pussy.
Greg: Oh My God.
by brendonb87 May 16, 2011