Alternate Static Source; Stall Warning System - Cirrus SR22 Pilot Operating Handbook

Section 7 Cirrus Design
Airplane Description SR22

Alternate Static Source

An alternate static pressure source valve is installed on the switch and
control panel to the right of the pilot's leg. This valve supplies static
pressure from inside the cabin instead of the external static port. If
erroneous instrument readings are suspected due to water or ice in
the pressure line going to the standard external static pressure source,
the alternate static source valve should be turned on. Pressures within
the cabin will vary with open heater/vents. Whenever the alternate
static pressure source is selected, refer to Section 5 airspeed
calibration and altitude for corrections to be applied.

Stall Warning System

The airplane is equipped with an electro-pneumatic stall warning
system to provide audible warning of an approach to aerodynamic
stall. The system consists of an inlet in the leading edge of the right
wing, a pressure switch and associated plumbing, and a piezo-
ceramic horn behind the instrument panel. As the airplane approaches
a stall, the low pressure on the upper surface of the wings moves
forward around the leading edge of the wings. As the low pressure
area passes over the stall warning sense inlet, a slight negative
pressure is sensed by the pressure switch. The pressure switch
completes a ground circuit causing the warning horn to sound, and
Serials 2044 and subsequent; the autopilot system to disconnect. The
warning horn provides a 94dB continuous 2800 Hz tone. The warning
sounds at approximately 5 knots above stall with full flaps and power
off in wings level flight and at slightly greater margins in turning and
accelerated flight. The system operates on 28 VDC supplied though
the 2-amp STALL WARNING circuit breaker on the Essential Bus.
With battery power on, the stall warning system preflight check is
accomplished as follows:
Stall warning system preflight check:
1. Use small suction cup and apply suction. A sound from the
warning horn will confirm that the system is operative.
7-92 P/N 13772-001
Revision A10