Copyright . The Boeing Company. See title page for details.
15.20.4  June 1, 2003

Warning Systems -System Description

YC153 -YK104
ANTI–ICE  ENG 
WINDOW  REVERSER 
OVERHEAT  EEC ALTN MODE 
PITOT HEAT  ENGINE CONTROL
COWL ANTI–ICE 
 
HYD  OVERHEAD 
OVERHEAT  EQUIP COOLING– OFF 
LOW PRESSURE  RIGHT SIDE GLARESHIELD ANTI-ICE ENG HYD OVERHEAD DOORS AIR COND  EMER EXIT LIGHTS–NOT ARMED FLIGHT RECORDER–OFF PASS OXY–ON PSEU YC411, YC413, YK101 - YK104 ELT
 DOORS  AIR COND 
FWD/AFT ENTRY  DUAL BLEED 
EQUIP  WING–BODY 
FWD/AFT CARGO  OVERHEAT 
FWD/AFT SERVICE  BLEED TRIP OFF 
LEFT/RIGHT  AUTO FAIL 
OVERWING  OFF SCHED DESCENT 
YC411, YC413  ZONE TEMP 
AIRSTAIR  PACK 

Warning Systems Takeoff Configuration Warning
The takeoff configuration warning is armed when the airplane is on the ground and either or both forward thrust levers are advanced for takeoff. An intermittent takeoff warning horn sounds if:
.
trailing edge flaps are not in the flaps 1 through 25 takeoff range, or

.
leading edge devices not configured for takeoff, or

.
SPEED BRAKE lever is not in the DOWN position, or

.
spoilers not down with the speedbrake lever in the DOWN position, or

Copyright . The Boeing Company. See title page for details.
Warning Systems -System Description 737 Flight Crew Operations Manual

.  
parking brake is set, or

.  
stabilizer trim not set in the takeoff range.

The warning indication is cancelled when the configuration error is corrected.
Landing Gear Configuration Warnings
Visual indications and aural warnings of landing gear position are provided by the landing gear indicator lights and landing gear warning horn.
Visual Indications
The landing gear indication lights are activated by signals from each gear, the LANDING GEAR lever, and the forward thrust lever position as follows:
Green light illuminated – landing gear is down and locked.
Red light illuminated –
.  
landing gear is in disagreement with LANDING GEAR lever position (in
transit or unsafe).

.  
landing gear is not down and locked (with either or both forward thrust

levers retarded to idle, and below 800 feet AGL). All lights extinguished – landing gear is up and locked with the LANDING GEAR lever UP or OFF.
Aural Indications
A steady warning horn is provided to alert the flight crew whenever a landing is attempted and any gear is not down and locked. The landing gear warning horn is activated by forward thrust lever and flap position as follows:
Flaps up through 10 –
.  
altitude below 800 feet RA, when either forward thrust lever set between
idle and approximately 20 degrees thrust lever angle or an engine not
operating and the other thrust lever less than 34 degrees. The landing gear
warning horn can be silenced (reset) with the landing gear warning
HORN CUTOUT switch

.  
if the airplane descends below 200 feet RA, the warning horn cannot be
silenced by the warning HORN CUTOUT switch.

Flaps 15 through 25 –
.  either forward thrust lever set below approximately 20 degrees or an
engine not running, and the other thrust lever less than 34 degrees; the
landing gear warning horn cannot be silenced with the landing gear
warning HORN CUTOUT switch.

Flaps greater than 25 –
.  regardless of forward thrust lever position; the landing gear warning horn
cannot be silenced with the landing gear warning HORN CUTOUT
switch.

Copyright . The Boeing Company. See title page for details.
15.20.6   September 26, 2003

Warning Systems -System Description 737 Flight Crew Operations Manual
The warning indication is cancelled when the configuration error is corrected.
Proximity Switch Electronic Unit (PSEU)
The PSEU monitors the following systems:
.
takeoff configuration warnings

.
landing configurations warnings

.
landing gear

. air/ground sensing. The PSEU, its sensors, and its input signals are monitored for internal faults. When designated faults are detected, a PSEU light on the aft overhead panel illuminates, and the OVERHEAD system annunciator light and MASTER CAUTION lights illuminate. The PSEU light can be reset following a maintenance BITE check or repair of the cause of the fault.
　
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