05/07/21
Message Overview:
Message Description:
The amber 'FIRE SYS FAULT' caution CAS message indicates the fire detection and extinguishing system has detected a fault.
- The FIREX CU provides Cold Start BIT, Warm Start BIT, Periodic BIT and Monitoring functions. If during these tests, the system detects a fault with both channels, the Control Unit sends the amber 'FIRE SYS FAULT' signal to the DCU for display.
Possible Causes:
- Fire-Detection-and-Extinguishing (FIREX) Control Unit (A91)
- Fwd Nacelle Loop B
- Associated Wiring
Troubleshooting Tips:
Advisory Wire/Service Bulletin:
- AW300-26-0249 - Landing GEAR BAY DET FAIL EICAS Message (20501 - 20999)
Forum Articles/Infoservice/Newsletter: None
Numerous FIREX Control Unit Internal failures (FIRE SYS FAULT cyan CAS message) and Gear Bay detection failures (GEAR BAY DET FAIL amber CAS message) are reported on in-service aircraft. The failure remains until the FIREX Control Unit is shutdown or replaced. Once cleared, failure cannot be repeated.
- In all cases the faults were cleared after replacing the FIREX Control Unit. Subsequent bench testing however declared the FIREX Control Units to be NFF and, as a result, the root cause of these events remains unknown. Kidde Aerospace suspects that the FIREX Control Unit operational environment may have an influence on the system operation.
Quick Links:
| Operational Test of the Fire-Detection-and-Extinguishing (FIREX) System | AMM 26-11-00-710-801 |
| 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 Forward-Nacelle Sensing Element | AMM 26-12-05-000-801 |
| Installation of the Forward-Nacelle Sensing Element | AMM 26-12-05-400-801 |
| 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 |
| Electrical Connectors - Maintenance Practice - ALL | SPM 20-20-00-02 |
Troubleshooting Recommendations:
Immediately following CAS message(s), and before removing the FIREX Control Unit, record the results of the inspections and voltage parameters as instructed in the table. Please ensure that this information is promptly reported to Bombardier Customer Support.
| Checks | Description | References | Findings |
|---|---|---|---|
| Inspections | Visually inspect the control unit for any obvious damage, or contamination | 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. | IPC @6-14-01 | Loop A107: Loop A108: |
|
| Voltages & Resistance | Record control unit input voltages utilizing a multi-meter or an oscilloscope. Take note especially of A91P1 pin 1 (+28 VDC Fire Det 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) | Wiring manual 26-13-01 CMM 26-11-88 (table 102) | Loop A107 to ground: ___ Ω Loop A108 to ground: ___ Ω |
|
| 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 |