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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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08/10/21

Message Overview:

Message Name:

CH A FAULT

Message Code:

B3-007404

Associated CAS:

AIR COND FAULT
(Advisory)

Reporting LRU: PK INLET T SNSR
System Description: 21-61-00
Schematic Diagram: 21-61-00
Wiring Diagram: 21-52-17

Message Description:

Channel A of the Pack Inlet Temperature Sensor are detected failed. Check for sensor failure.

Possible Causes:

  • Pack Inlet Temperature-Sensor (PITS) (MT25)
  • Integrated Air System Controller (IASC1) (A55)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Quick Links:

Removal of the Pack Inlet Temperature-Sensor AMM 21-61-33-000-801
Installation of the Pack Inlet Temperature-Sensor AMM 21-61-33-400-801
Operational Test of the Bleed Air System AMM 36-11-00-710-801
Standard Practices - Replace Wiring SPM 20-12-00-02
Standard Practices - Wire Repair SPM 20-12-10-02

Troubleshooting Recommendations:

  1. Reset PRESS 1 / PACK circuit breaker CB1-D14, L WING / BLD LK circuit breaker CB1-E10.

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.

  2. Check resistance of Pack Inlet Temperature Sensor MT25 between pins 1 and 3.

    1. If resistance is within tolerance, go to step 4.
    2. If resistance is out of tolerance, continue with next step.

      Temp in °C Temp in °F Resistance in Ω
      -65 -85 148.4
      -60 -75 152.4
      -50 -58 160.4
      -40 -40 168.4
      -30 -22 176.3
      -20 -4 184.3
      -10 14 192.2
      0.0 32 200.0
      10 50 207.8
      20 68 215.6
      30 86 223.36
      40 104 231.1
      50 122 238.8
      60 140 246.5
      70 158 254.0
      Temp in °C Temp in °F Resistance in Ω
      80 176 261.8
      90 194 269.4
      100 212 277.0
      110 230 284.6
      120 248 292.1
      130 266 299.6
      140 284 307.1
      150 302 314.6
      160 320 322.0
      170 338 329.4
      180 356 336.8
      190 374 344.2
      200 392 351.5
      210 410 258.9
      220 428 366.1
      Temp in °C Temp in °F Resistance in Ω
      230 446 373.4
      240 464 380.7
      250 482 387.9
      260 500 395.1
      270 518 402.3
      280 536 409.4
      290 554 416.5
      300 572 423.6
      310 590 430.7
      320 608 437.8
      330 626 444.8
      340 644 451.8
      350 662 458.8
      360 680 465.8
      370 698 472.7

  3. Replace PIT sensor, (or interchange with Compressor Discharge Temperature sensor MT25).

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.

  4. Do wiring checks between IASC1 A55P1 (pins 48 & 65) and PIT MT25 (pins 1 & 3). Repair as required.

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.

  5. Interchange IASCs.
  6. Do close out.

pits

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