5.5 Tactile signals. If tactile signals are used, they
should be of such amplitude as to be detected by the part of the body being
stimulated, and should be delivered by an apparatus that will always be in
contact with the body. Tactile signals shall also be coded such that they
could not be misconstrued as a normal vibration of the equipment or crew
station. Any use of tactile signals in aircrew stations must have prior
approval by the acquiring activity (see 6.3.1).