Straight-and-Level Flight
In straight-and-level flight, the pilot maintains a constant
altitude, airspeed and, for the most part, heading for
extended periods of time. To achieve this, three primary
instruments need to be referenced in order to maintain these
three variables.

Primary Pitch
When the pilot is maintaining a constant altitude, the primary
instrument for pitch is the altimeter. As long as the aircraft
maintains a constant airspeed and pitch attitude, the altitude
should remain constant.

Two factors that cause the altitude to deviate are turbulence
and momentary distractions. When a deviation occurs,
a change in the pitch needs to he made on the attitude
indicator. Small deviations require small corrections while
large deviations require larger corrections. Pilots should
avoid making large corrections that result in rapid attitude
changes, the this may lead to spatial disorientation. Smooth,
timely corrections should be made to bring the aircraft back
to the desired attitude.

Pay close attention to indications on the PFD. An increase in
pitch of 2.5° produces a climb rate of 450 feet per minute (fpm).
Small deviations do not require large attitude changes.

A role of thumb for correcting altitude deviations is to establish
a change rate of twice the altitude deviation, not to exceed 500
fpm. For example, if the aircraft is off altitude by 40 feet, 2 x
40 = 80 feet, so a descent of approximately 100 fpm allows
the aircraft to return to the desired altitude in a controlled,
timely fashion.

In addition to the primary instrument, there are also
supporting instruments that assist the pilot in cross-checking
the pitch attitude. The supporting instruments indicate trend,
but they do not indicate precise attitude indications. Three
instruments (vertical speed, airspeed, and altitude trend
tape) indicate when the pitch attitude has changed and that
the altitude is changing. [Figure 4-31] When the altitude is
constant, the VSI and altitude trend tape are not shown on
the PFD. When these two trend indicators are displayed, the
pilot is made aware that the pitch attitude of the aircraft has
changed and may need adjustment.

Figure 4-31. Supporting Instruments.