by Jonathan M. Stern
Straight and Level Flight
Straight and level flight is, as its name suggests, flight conducted at a constant altitude on a constant heading. Any deviation from the desired altitude or heading should be immediately corrected.
Deviation from altitude must be determined by reference to the altimeter, because it is nearly impossible to "eyeball" altitude with any specificity. If the airplane has gone below the desired altitude, you increase the pitch altitude to return to the desired altitude and then to a lesser extent to maintain the desired altitude. To maintain straight flight, select two points on the ground along the desired track (see Figure 4.2).
Figure 4.2. It is helpful to select two ground reference points aligned with the desired course.
Be sure to promptly correct any deviation from alignment with those points by turning back to the desired heading. Deviation from heading also can be determined by checking that both wing tips remain in the same position relative to the horizon. In coordinated flight, the airplane changes heading only if it is banked. Cross-checking the attitude indicator, which shows bank, and the heading indicator also helps identify any deviation from the desired heading.