BY ORDER OF THE SECRETARY OF THE AIR FORCE AIR FORCE ...

364
AFMAN 11-217V1 3 JANUARY 2005
plane. This has also been called a “cross-coupling” sensation. If pilots try to correct
for the illusion without referencing their flight instruments, they may put the aircraft
in a dangerous attitude. The coriolis illusion is probably not as important in fixed
wing aircraft because the relatively low turn rates of instrument flight make coriolis
illusion very difficult to generate. However, care should be used during rotary-wing
flight. These aircraft have the ability to generate significant yaw rates.
Figure 17.5. The Coriolis Illusion and the Leans.
17.3.1.3. The Leans. This is the most common vestibular illusion and is caused by
rolling or banking the aircraft after the pilot has a false impression of the true vertical.
After a prolonged turn has ceased, the pilot may perceive the roll to wings level as a
bank and turn in the opposite direction. This can cause pilots to lean in an attempt to
assume what they think is a vertical posture. If they establish a very slow roll to the
left that does not stimulate the vestibular apparatus and then roll rapidly to the right to
level flight, they may generate the false impression of only having rolled to the right,
and the leans may result. The leans are most commonly felt when flying formation
on the wing in and out of the weather or at night. Since the wingman’s attention is on
the flight lead and not on the attitude display, it becomes easy for the vestibular or
somatosensory system to provide false orientation cues, often reinforced by false
ambient visual cues. These false orientation cues can quickly convince the wingman
of being in an “unusual” attitude and cause a strong case of the leans. To minimize
the effects of the leans while on the wing, it is important for the wingman to