.
when the thrust levers are advanced toward takeoff power
.
for 30 seconds after landing.
Mach/Airspeed Warning System
Two independent Mach/airspeed warning systems provide a distinct aural warning, a clacker, any time the maximum operating airspeed of Vmo/Mmo is exceeded. The warning clackers can be silenced only by reducing airspeed below Vmo/Mmo.
The airspeed indicator displays red warning bands indicating maximum and minimum airspeeds. Amber bands indicate maximum and minimum maneuvering airspeeds.
When either an overspeed condition or a system test occurs, the ADIRU transmits a signal to the aural warning module, sounding the clacker. The system can only be tested on the ground.
Stall Warning System
Natural stall warning (buffet) usually occurs at a speed prior to stall. In some configurations the margin between stall and natural stall warning is less than desired. Therefore, an artificial stall warning device, a stick shaker, is used to provide the required warning.
Copyright . The Boeing Company. See title page for details.
Warning Systems -System Description
737 Flight Crew Operations Manual
The stall warning “stick shaker” consists of two eccentric weight motors, one on each control column. They are designed to alert the pilots before a stall develops. The warning is given by vibrating both control columns. The system is armed in flight at all times. The system is deactivated on the ground.
Two independent, identical stall management yaw damper (SMYD) computers determine when stall warning is required based upon:
.
alpha vane angle of attack outputs
.
ADIRU outputs
.
anti–ice controls
.
wing configurations
.
air/ground sensing
.
thrust
.
FMC outputs.
YA613, YA809, YD651 - YK104
.
mach compensation The SMYD computers provide outputs for all stall warning to include stick shaker
and signals to the pitch limit indicator and airspeed displays and the GPWS windshear detection and alert.
Two test switches are installed in the aft overhead panel. Pushing either of these initiates a self–test of the respective stall warning channel. The No.1 activates the Captain stick shaker, and the No. 2 activates the F/O stick shaker. Either stick shaker vibrates both columns through column interconnects.
Altitude Alerting System YA613 - YA809, YC411 - YK104
Altitude alerting occurs when approaching or departing the MCP–selected altitude. Altitude alerting is inhibited when trailing edge flaps are extended to 25 or greater, or while G/S is captured.
Acquisition Alerting
900 feet before reaching the selected altitude, a white box shows around the selected altitude display and the box around the current altitude becomes bold. A momentary tone sounds. At 300 feet from selected altitude, the selected altitude box no longer shows.
Copyright . The Boeing Company. See title page for details.
15.20.8 June 1, 2005
Warning Systems -System Description
Deviation Alerting
When deviating by 300 feet from the selected altitude, a momentary tone sounds and the current altitude box turns amber and begins to flash. The amber flashing continues until:
.
altitude deviation becomes less than 300 feet
.
altitude deviation becomes more than 900 feet
.
a new altitude is selected.
Altitude Alert Profile
NO INDICATIONS
Acquisition - Aural warning tone momentarily sounds. A box shows around the selected altitude display and the box around current altitude becomes bold.
Deviation - Aural warning tone momentarily soundsand current altitude box turns amber and flashes.
Altitude Alerting System YC153, YC154
Altitude alerting occurs when approaching or departing the MCP–selected altitude. Altitude alerting is inhibited when trailing edge flaps are extended to 25 or greater, or while G/S is captured.
Copyright . The Boeing Company. See title page for details.
Warning Systems -System Description
Acquisition Alerting
900 feet before reaching the selected altitude, a white box shows around the selected altitude display and the box around the current altitude becomes bold. A momentary tone sounds. At 200 feet from selected altitude, the selected altitude box no longer shows.
Deviation Alerting
When deviating by 200 feet from the selected altitude, a momentary tone sounds and the current altitude box turns amber and begins to flash. The amber flashing continues until:
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