If alternate static pressure is used in level flight, what should the pilot expect?

When alternate static pressure is used in level flight, the pilot should expect that the altimeter will read higher than normal. This phenomenon occurs because alternate static pressure is typically lower than the ambient static pressure outside of the aircraft. When the pilot switches to alternate static, it introduces a difference in pressure that affects the altimeter reading. The altimeter relies on the ambient static pressure to determine altitude; if the static pressure decreases, the altimeter interprets this as the aircraft being at a higher altitude than it actually is.

This situation typically arises when there is a malfunction or blockage affecting the primary static pressure source, leading to inaccurate readings. Therefore, when using alternate static, pilots need to be aware of potential discrepancies in their altimeter readings, ensuring they adjust their altitude awareness accordingly.