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(WARNING)
RED MESSAGE (CAUTION)
AMBER MESSAGE (ADVISORY)
CYAN MESSAGE (STATUS)
WHITE MESSAGE Require immediate crew attention. These messages are accompanied by flashing master warning, triple chime attenson with or without voice message or dedicated tone. Require immediate crew awareness and future crew action may be required in the form of alternate system selection or performance limitation. These message are accompanied by flashing master caution and a single chime. Indicate safe or normal system operation which require crew awareness, over and above the dark cockpit philosophy. Indicate minor failures or reduction in systems capability, which require no crew action.

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02/26/21

Message Overview:

Message Name:

SHORT CIRCUIT

Message Code:

B3-008158

Associated CAS:

GEAR BAY DET FAIL
(Caution)

Reporting LRU: MWW OVHT LOOP
System Description: 26-14-00
Schematic Diagram: 26-14-00
Wiring Diagram: 26-11-05
26-13-01

Message Description:

Short circuit on Main Wheel Well loop element A107, A108 wire short, or FIREX Control Unit internal failure.

Possible Causes:

  • Main Landing Gear (MLG) Sensing Element (A107)
  • Main Landing Gear (MLG) Sensing Element (A108)
  • Fire-Detection-and-Extinguishing Control Unit (FIREX CU) (A91)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Quick Links:

Removal of the Fire-Detection-and-Extinguishing (FIREX) Control-Unit AMM 26-11-01-000-801
Installation of the Fire-Detection-and-Extinguishing (FIREX) Control-Unit AMM 26-11-01-400-801
Removal of the Gearbox Sensing Element AMM 26-12-13-000-801
Installation of the Gearbox Sensing Element AMM 26-12-13-400-801
Functional Test of the Main Landing Gear (MLG) Overheat-Detection System AMM 26-14-00-720-801
General Visual Inspection of the Main Landing Gear (MLG) Wheel Well Ground Wire and Terminal AMM 26-14-00-210-801
Removal of the Main Landing Gear (MLG) Sensing Element AMM 26-14-01-000-801
Installation of the Main Landing Gear (MLG) Sensing Element AMM 26-14-01-400-801
Electrical Bonding - Adjustment/Test SPM 51-80-00-05
Wiring - Maintenance Practices - ALL SPM 20-12-00-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02

Troubleshooting Recommendations:

  1. Immediately following CAS message(s), and before removing the FIREX Control Unit (A91), record temperature, condition and voltage parameters as instructed in the table. Please ensure that this information is promptly reported to Bombardier CRC & Customer Support ac.yul@aero.bombardier.com.
  2. Check the resistance from the FIREX Control Unit (A91) on plug A91P3 between pins 11 and 12, there should be > 6Ω resistance. Check for a dead short between either pin to ground.
  3. If this is short to ground, Perform the general visual inspection of the main landing gear wheel well ground wire and terminal IAW TASK 26-14-00-210-801. Pay particular attention to the terminals on the wheel bin connector.
  4. If the gear bay loops check good, replace the FIREX Control Unit IAW TASK 26-11-01-000-801, TASK 26-11-01-400-801.
  5. Perform the functional test of the main landing gear overheat detection system IAW TASK 26-14-00-720-801.

21_firex_cu_install14_wheelwell_overheat_detection_sensor14_wheelbin_connector14_wheelwell_overheat_block

Checks Description References Findings
Temperatures Approximate temperature level of the equipment bay where the FIREX control unit is located Location in IPC 26-11-01 T = ___ °C /°F
Note the approximate amount of time the control unit may have been exposed to extreme hot, or cold temperature (above 70°C or below -40°C) Time = _______
Inspections Visually inspect the control unit for any obvious damage, or contamination IAW TASK 26-12-13-400-801 IPC 26-11-01, Figure 1- Item: 5 Condition:
Record the condition of loop connections and connectors. Look at connections for evidence of contamination or corrosion at the point of contact. Record any damage to the connector, or center-wire pin. Perform the electrical bonding check of the loops IAW AMM TASK 51-80-00-760-801 IPC 26-14-01 Loop A107:
Loop A108:
Voltages & Resistance Record control unit input voltages utilizing a multimeter or an oscilloscope. Take note especially of A91P1 pin 1 (+28 VDC FireDet A) input. Wiring manual 26-11-05 A91P1 - 1: ____ VDC - Should be 28 VDC
A91P1 - 3: ____ VDC - Should be 28 VDC
A91P1 - 9: ____ VDC - Should be Ground
A91P1 - 15: ____ VDC - Should be Ground
A91P1 - 63: ____ VDC - Should be Ground
A91P2 - 1: ____ VDC - Should be 28 VDC
A91P2 - 3: ____ VDC - Should be 28 VDC
A91P2 - 9: ____ VDC - Should be Ground
A91P2 - 15: ____ VDC - Should be Ground
A91P2 - 63: ____ VDC - Should be Ground
Disconnect the sensing elements loops from the control unit. Record the insulation resistance of each sensing element loops between the center-wire and a chassis ground. (Refer to CMM 26-11-88) Wiring manual 26-13-01 CMM (table 102) Loop A107 to ground: ___ Ohms should be 3.08Ω
Loop A108 to ground: ___ Ohms should be 3.08Ω
Monitor the AC ripple or noise signal of sensing element loops with an oscilloscope. Take note of any excess noise that may cause the system to fail the Periodic BIT (PBIT) test. Wiring manual 26-13-01 CMM 26-11-88 (Table 102) Copy or print noise signal
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