Hehe.
Ok, now I'll give you the "real" answer. At least the answer if you are talking about air combat.
If you draw a line from one wingtip to the other of an airplane, you will roughly get it's "plane" of movement. If you roll your craft so that your wingline is at a different angle than the other fellow's, you can say you are "out of plane". This is best demonstrated if your target rolls 90 degrees left and pulls. If you only roll 45 degrees and pull, you will be 45 degrees out of plane with him. Visualize it as if you both executed perfect 360 degree circles at this bank angle drawing a line in the sky. The two circles represent the planes. One circle is "flat" or horizontal, while yours would be tilted up at about 45 degrees.
You normally want to do "out of plane" maneuvers for a couple of reasons, either to avoid getting shot, or to avoid high closure or an overshoot. When a bad guy is camped out at your six, it is easy for him to make adjustments "in plane". That is if you are both flying along wings level, an adjustments you make up or down will be fairly easy for him to track and shoot you. However, if you can roll and pull out of plane with him but 90 degrees or so, he has to make a much more difficult correction to track you. In this way a plane with very fast roll can be very difficult to shoot if the pilot keeps rolling quickly out of plane with the attacker and making short hard pulls.
The second circumstance when out of plane maneuvers are normally used is when you have high closure and want to drop into lag pursuit to avoid an overshoot. If the Spit I'm tracking makes a hard flat turn to the left, I can use an out-of-plane maneuver avoid overshooting and set myself up for a shot. I do this by simply rolling to only about 40 degrees and pulling, thus taking me out of plane. I'll have to roll much further an pull later on to get back down to the enemy, but you get the idea.
This effectively means I am going to have to travel a longer distance to get where he is going. Since I have more energy, I need to do this to avoid overshooting him. A high yoyo such as I just described is an example of an out of plane maneuver. The most extreme example is when your target flat turns and you execute a loop. That's as far out of plane as you can get.
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Lephturn - Chief Trainer
A member of The Flying Pigs
http://www.flyingpigs.com "A pig is a jolly companion,
Boar, sow, barrow, or gilt --
A pig is a pal, who'll boost your morale,
Though mountains may topple and tilt.
When they've blackballed, bamboozled, and burned you,
When they've turned on you, Tory and Whig,
Though you may be thrown over by Tabby and Rover,
You'll never go wrong with a pig, a pig,
You'll never go wrong with a pig!"
-- Thomas Pynchon, "Gravity's Rainbow"
[This message has been edited by Lephturn (edited 11-30-2000).]