Technical data

13773-001
27-31
Page 1
STALL WARNING SYSTEM
1. DESCRIPTION
The airplane utilizes an electro-pneumatic stall warning system to indicate an approach to aerodynamic
stall. As the angle of attack increases and the airplane approaches an aerodynamic stall, the stagnation
point moves lower on the leading edge causing low pressure on the upper leading edge to increase. As low
pressure passes over the stall warning port located on the leading edge of the wing, negative pressure is
sensed by a pressured switch which activates the stall warning horn. The pressure switch, located on the
left side panel of the mid-console, forward of the circuit breaker panel, is a normally open, diaphragm-oper-
ated switch. The stall warning horn, located on the top flange of the left-center console rib, is a piezo-
ceramic audio indicator which, when achieved, supplies a continuous 94 dB, 2800 Hz tone.
Primary VDC power is supplied through the 2-amp ANNUNCATOR POWER circuit breaker on the Essen-
tial Bus. In the case of emergency procedures that require the MASTER switch to be turned OFF, power is
supplied to the stall warning system directly from the airplane battery on the clock circuit. In addition, this
provides a ground check of the stall warning system with the power off. In the event of a total electrical fail-
ure, power for the stall warning system is supplied by the turn coordinator battery back-up by turning the
EMERG. switch ON.
2. MAINTENANCE PRACTICES
A. Stall Warning Pressure Switch (See Figure 27-311)
(1) Removal - Stall Warning Pressure Switch
(a) Ensure AVIONICS and MASTER switches are in OFF position.
(b) Pull ANNUCIATOR POWER circuit breaker.
(c) Remove LH mid-console circuit breaker trim panel.
(d) Open circuit breaker panel.
(e) Remove nuts, washers, and screws securing pressure switch to console.
(f) Disconnect electrical leads from pressure switch.
(g) Disconnect stall warning line form pressure switch and remove switch from airplane.
(2) Installation - Stall Warning Pressure Switch
(a) Position pressure switch on console and install screws, washers, and nuts.
(b) Connect stall warning line to pressure switch.
(c) Connect electrical leads to pressure switch.
(d) Close circuit breaker panel.
(e) Reset ANNUCIATOR POWER circuit breaker.
(f) Install LH mid-console circuit breaker trim panel.
(g) Perform Stall Warning Operational Check - Ground. (Refer to 27-31)
(h) Perform Stall Warning Operational Check - Flight. (Refer to 27-31)
(3) Inspection/Check - Stall Warning Operational Check - Ground
(a) Acquire necessary tools, equipment, and supplies.
(b) Ensure leading edge surrounding stall warning port, located on RH wing leading edge, is
clean.
Description P/N or Spec. Supplier Purpose
Suction Cup - Any Source Application of neg-
ative pressure.
30 Nov 2000