NASA's Paul Hill goes into more detail below about specific UFO flight characteristics and there's also a good section dealing with the subject taken from NICAP's 'UFO Evidence' report - the RAF Topcliffe incident is also posted but if anyone knows of any more case examples then please post away.
Peculiar behaviour such as falling leaf or pendulum motion during vertical descent has been independently reported many times by UFO witnesses in widely separated parts of the world..
Pendulum/Falling Leaf Motion
A curious, but fairly common, flight characteristic of UFOs is a pendulum-like motion (swaying back and forth) during hovering, slow climb, or descent. Witnesses frequently have compared this to the gyrations of a falling leaf.
A very similar pendulum-like motion, occurring as a UFO travels in a horizontal plane (rather than ascending or descending) has been noticed occasionally. It consists of a side-to-side oscillation as the UFO proceeds in a constant direction.
SECTION XII - PATTERNS
Paul Richard Hill - NASA Aerodymanicist:
Maneuvers. Hovering at any altitude is common. UFOs hover close to the ground for long times instead of landing. The different maneuvers include:a. falling leaf or UFO-rock like a coin falling in water
b. silver-dollar wobble - like a coin with a slow spin on a flat surface. This maneuver is consistently observed at the end of a rapid descent as the UFO initiates hovering
c. acute-angle turn with rapid stop at the vertex
d. sudden reversal of direction
e. bank and turn - exactly like conventional aircraft
f. straight-away speed run either horizontal or vertical
g. tilt to maneuver "UFOs tilt to perform all maneuvers ... they sit level to hover, tilt forward to move forward, tilt backward to stop, bank to turn"
'Ufology' by James M. McCampbell
UFO Flight - Maneuver