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

AFMAN 11-217V1 3 JANUARY 2005 365
occasionally cross-reference the attitude display, without making a head movement if
possible. Thus, the pilot must use focal vision to overcome the false cues and to
acquire accurate spatial orientation information.
Figure 17.6. The Leans.
17.3.1.4. Somatogravic Illusion. The otolith organs are responsible for a set of
illusions known as somatogravic illusions. This type of illusion is the sensation of
change in attitude when the otolith organs are stimulated by linear acceleration. This
illusion was first noted in the US Navy during aircraft carrier launch operations. A
false nose high sensation can occur when an aircraft accelerates forward in level
flight. This somatogravic illusion may be unrecognized during an IMC takeoff or
missed approach acceleration if the pilot is not concentrating on flying instruments.
Correcting for this illusion during climbout could cause the pilot to dive the aircraft
into the ground. A false nose-down sensation can occur as a result of rapid
deceleration in the weather.
17.3.1.4.1. Inversion illusion. A variant of somatogravic illusion is the inversion
illusion, in which G forces act on the otolith organs to give the pilot transitioning
from an upright position to one of feeling upside down. Although the inversion
illusion is of greatest magnitude in high-performance aircraft, it can occur in any
aircraft. The pilot can overcome the illusion by paying attention to valid external
visual references or to aircraft attitude instruments.