(2)
The wing and lower aft body overheat detection system is divided into two sections; the left and right overheat sections. The right overheat section consists of sensing elements connected in series with the right overheat control unit to form a closed circuit sensing loop. The left overheat section consists of sensing elements connected in series through three test switches to the left and APU overheat control unit to form a closed circuit sensing loop. The test switches on the compartment overheat accessory unit enable a malfunction in the left overheat section to be isolated.
(3)
The overheat detection system can be tested on the ground and in flight by an overheat test switch on the air conditioning module. The overheat test switch tests continuity through the wings and lower aft body by simulating an overheat condition, thereby energizing the warning lights. If the left detection system fails to test, the area of the malfunction can be isolated to one of the four sections of the airplane by operating the auxiliary test switches on the compartment overheat accessory unit.
(4)
The right sensing loop elements are at engine 2-strut cavity, right wing bleed air duct, right wing leading edge, and right air conditioning packs. The left sensing loop elements are at engine 1 strut cavity, left wing bleed air duct, left wing leading edge, left air conditioning packs, keel beam, aft cargo compartment, and APU cavity.
500
Feb 20/90 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 26-18-0 Page 1
H28184
Wing and Lower Aft Body Overheat Detection System Component Location 500
26-18-0 Figure 1 (Sheet 1) Nov 15/69
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
500 Wing and Lower Aft Body Overheat Detection System Component Location
Feb 20/90 Figure 1 (Sheet 2) 26-18-0
Page 3
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
EFFECTIVITY
AIRPLANES WITH BOEING
M237 COMPARTMENT
OVERHEAT ACCESSORY UNIT
G42441
Wing and Lower Aft Body Overheat Detection System Schematic 500
26-18-0 Figure 2 Feb 20/90
Page 4
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
C. Airplanes with electronic Fenwal M237 engine overheat accessory unit:
(1)
The wing and lower aft body overheat detection system consists of an overheat test switch and overheat lights on air conditioning module P5-10, compartment overheat accessory unit, master caution lights, and sensing elements. The sensing elements are connected to the compartment overheat accessory unit. The accessory unit contains a control card which has a microprocessor and a relay board which monitor the resistance of the sensing elements. When a temperature rise causes the resistance to drop to a value corresponding to the alarm temperature, the compartment overheat accessory unit will provide a signal to the applicable warning light and the master caution light control section in the air conditioning module. When an alarm/fault condition is found, the condition is stored in the non-volatile memory of the Fenwal compartment overheat accessory unit, the MAINT ADV light will illuminate when a condition is stored in memory. The MAINT ADV light will not extinguish until the condition is corrected and the memory is cleared.
(2)
The wing and lower aft body overheat detection system is divided into left and right sections. The right overheat section consists of a single detector loop with sensing elements connected in series. The left overheat section consists of four separate detector loops with sensing elements connected in series. All five loops are monitored by the control card in the compartment overheat accessory unit. The compartment overheat accessory unit can isolate an alarm/fault condition to each of the five loops which can be displayed as a code on the LED display. The codes, as defined on the compartment overheat accessory unit cover plate, isolate the condition to the specific location and condition; an alarm, an open loop fault, or a short circuit loop fault.
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