How is the airspeed indicator affected when using an alternate static source?

How is the airspeed indicator affected when using an alternate static source?

• A. It indicates slower than actual
• B. It indicates faster than actual
• C. It remains unchanged
• D. It fluctuates unpredictably

Answer: (B)

Using an alternate static source can indeed lead to the airspeed indicator indicating a faster speed than actual. This occurs because the alternate static source often has a different static pressure than the primary source, especially if the aircraft is in turbulent air or experiencing a significant climb or descent. When the static pressure is lower than the ambient air pressure (as it often will be when using an alternate source within the cabin), the airspeed indicator is presented with a reduced pressure, causing it to read a higher airspeed than what is true. In typical operations, when the alternate static source is utilized, the altitude may be lower relative to the normal static pressure or atmospheric conditions, further contributing to this discrepancy. Therefore, it is crucial for pilots to understand this phenomenon, as it can lead to miscalculations in speed, affecting navigation and safety. Awareness of how the alternate static source might alter instrument readings is vital in IFR conditions.

Using an alternate static source can indeed lead to the airspeed indicator indicating a faster speed than actual. This occurs because the alternate static source often has a different static pressure than the primary source, especially if the aircraft is in turbulent air or experiencing a significant climb or descent. When the static pressure is lower than the ambient air pressure (as it often will be when using an alternate source within the cabin), the airspeed indicator is presented with a reduced pressure, causing it to read a higher airspeed than what is true.

In typical operations, when the alternate static source is utilized, the altitude may be lower relative to the normal static pressure or atmospheric conditions, further contributing to this discrepancy. Therefore, it is crucial for pilots to understand this phenomenon, as it can lead to miscalculations in speed, affecting navigation and safety. Awareness of how the alternate static source might alter instrument readings is vital in IFR conditions.