When we fly under VFR, we control the airplane by making use of visual references. We establish the desired pitch and roll attitude by comparing visible parts of the airplane, such as the engine cowling or glare shield, to the horizon.
When these outside references are not available, our inside references, the flight instruments, can be used. We still fly the airplane the same way. The flight instruments are merely substituted for the outside references we are accustomed to using.
The goal is still the same. We want to place the airplane in the desired attitude and keep it there at all times during the flight. Some instruments give us information concerning the airplane’s pitch attitude, while others give us information about roll attitude. The attitude indicator is the only flight instrument that directly indicates pitch and roll attitude simultaneously. The other instruments indicate either pitch or roll information, and they do so indirectly. For example, if the heading indicator shows a right turn, it can be inferred that the airplane is banked to the right and that the rate of heading change is correlated with bank angle.
The pitch instruments are the airspeed indicator, attitude indicator, altimeter, and vertical speed indicator. The bank instruments are the attitude indicator, turn coordinator, and heading indicator. The power instruments are the airspeed indicator and the aircraft's manifold pressure gauge or tachometer.
For each maneuver, one flight instrument will provide us a primary reference for pitch, and one will provide a primary reference for roll. Other instruments act as secondary instruments for pitch and roll. Which instruments are primary and secondary change, depending on which is displaying the most pertinent information. To better understand how to use inside references, let’s look at how the primary and secondary instruments vary through a typical flight.
The three fundamental skills involved in all instrument flight maneuvers are the instrument cross check, instrument interpretation, and aircraft control.