When leak checking an unpressurized aircraft's static pressure system, which instrument may be used in lieu of a pitot-static system tester?

The use of an altimeter in lieu of a pitot-static system tester for leak checking an unpressurized aircraft's static pressure system is appropriate because the altimeter is directly connected to the aircraft's static system. When performing a leak check, the altimeter can be utilized to detect whether it retains pressure as changes in static pressure occur. If the altimeter indicates a steady reading during a pressure change, it suggests that the static system is intact and free of leaks.

In contrast, the cabin altimeter, airspeed indicator, and vertical speed indicator may not provide reliable results for this specific check. The cabin altimeter is calibrated for different pressure ranges and may not reflect the same values as a regular altimeter that is directly tied to the static pressure system. Airspeed indicators and vertical speed indicators, while they do rely on the static pressure system, ultimately serve different functions and could give distorted readings during the leak check process due to their reliance on dynamic pressure or different calibration mechanisms. Therefore, the altimeter is the most valid instrument for this leak check scenario.