Aircraft Instrument Systems When an unpressurized aircraft’s static pressure system is leak checked to comply with the requirements of Section 91.411, what aircraft instrument may be used in lieu of a pitot-static system tester? 1. Vertical speed indicator. 2. Cabin altimeter. 3. Altimeter. 4. Cabin rate-of-change indicator. 5. Airspeed indicator. a. 1 or 5. b. 2 or 4. c. 3.