Rotation in Three Dimensions - 3D Math Primer for Graphics and Game Development - page 231

Step 3. After heading has been applied, pitch measures the amount of
rotation about the x-axis. This is the object-space x-axis, not the
upright x-axis. Staying consistent with the left-hand rule, positive
rotation rotates downward. In other words, pitch actually measures
the angle of declination. This is illustrated in Figure 8.6.
Figure 8.6
Step 3: Pitch is the second rotation and rotates
about the object lateral axis
Step 4. After heading and pitch angles have been applied, bank measures
the amount of rotation about the z-axis. Again, this is the object-
space z-axis, not the original upright-space z-axis. The left-hand
rule dictates that positive bank rotates counterclockwise when viewed
from the origin looking towards +z. This is illustrated in Figure 8.7.
Figure 8.7
Step 4: Bank is the third and final rotation and
rotates about the object longitudinal axis
It may seem contradictory that positive bank is counterclockwise,
since positive heading is clockwise. But notice that positive heading
is clockwise when viewed from the positive end of the axis towards
the origin, the opposite perspective from the one used when judging