07/17/23
Message Overview:
Message Description:
The FQGC has detected a discrepancy in the left collector tank fuel quantity probe circuit (L probe 7).
- Left tank quantity and total quantity are replaced with magenta dashes.
- The fault can be triggered by the presence of water in the probe.
Possible Causes:
- Water Contamination
- Fuel Quantity Gauging Computer (FQGC) (A57)
- Fuel Quantity Probe (No. 7) (LH) (MT17)
- Associated Wiring
Troubleshooting Tips:
Advisory Wire/Service Bulletin:
- AW300-28-0118 No Fault Found Initiative: Fuel Quantity and Gauging Computer (FQGC)
- AW300-28-0138 Fuel Tank Sumping
Forum Articles/Infoservice/Newsletter: None
- Because water has a higher dielectric constant than fuel, water in fuel tanks will affect the reading of fuel quantity probes if it comes in contact with them. The reading will become out of range and the FQGC will stop sending fuel quantity for that tank (magenta dashes).
- When sumping water from affected fuel tank it is preferable to have the fuel probe immersed in fuel, in order for the water to pool at the bottom of the fuel tank.
- To get most of the water to the bottom of the tank, do not move aircraft for at least 2 hours before sumping.
| Fuel Probes Capacitance | ||||
|---|---|---|---|---|
| EMPTY TANK | FULL TANK | OUT OF RANGE | ||
| PROBE | VALUE pf | PROBE | VALUE pf | VALUE pf |
| 1 | 29 | 1 | 53 | <25.88 or >65.1 |
| 2 | 29.1 | 2 | 56.8 | <25.88 or >65.1 |
| 3 | 29 | 3 | 56.8 | <25.88 or >65.1 |
| 4 | 34.1 | 4 | 67.4 | <30.83 or >77.16 |
| 5 | 40.8 | 5 | 80.1 | <37.13 or >91.93 |
| 6 | 63.8 | 6 | 127.1 | <58.66 or >146.01 |
| 7 | 59.7 | 7 | 118.4 | <54.8 or >136.2 |
| 8 | 79.5 | 8 | 158.6 | <72.94 or >181.43 |
| 9 | 63.7 | 9 | 126.9 | <58.66 or >146.01 |
| 10 | 66 | 10 | 128.2 | <121.39 or >138.42 |
Quick Links:
| Pressure Refueling | AMM 12-11-01-650-801 |
| Suction Defueling | AMM 12-11-09-650-801 |
| Drain Water from the Fuel Tank | AMM 28-10-00-680-801 |
| Built-In Test of the Fuel-Quantity Gauging System | AMM 28-41-00-740-801 |
| Removal of the Fuel Quantity Computer | AMM 28-41-01-000-801 |
| Installation of the Fuel Quantity Computer | AMM 28-41-01-400-801 |
| Removal of the Fuel Quantity Probe | AMM 28-41-13-000-801 |
| Installation of the Fuel Quantity Probe | AMM 28-41-13-400-801 |
| Capacitance Check of the Fuel Quantity Probes | AMM 28-41-13-760-801 |
| Cleaning of the Fuel Quantity Probes | AMM 28-41-13-160-801 |
| 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:
- If the MDC fault code is in the FAULT HISTORY and the left fuel tank indication is not dashed, no action is required, but it is recommended to sump fuel from the left tank in case water was the cause of the failure.
- If the MDC fault code is in the CURRENT FAULT, do the Capacitance Check of the Fuel Probes.
- If the reading for L PR07 is under 54.8pF, check wiring from FQGC to left probe 7. If wiring is found serviceable, replaced probe.
- If the reading for L PR07 is over 136.2pF, sump at least 2 gallons of fuel from the left fuel tank or until no water is found. If fault continues, go to next step.
- Re-rack the Fuel Quantity Gauging Computer (FQGC). Is the fault message still present?
- If YES, go to next step.
- If NO, do close out.
- Defuel the aircraft. If fault continues, go to next step.
- Access the Left Tank Probe 7.
- Check probe for loose electrical connections.
- Clean probe (AMM 28-41-13-160-801).
- If fault continues, go to next step.
- Check wiring from FQGC to left tank probe 7. If wiring is found serviceable, replace left tank fuel probe 7.
- If fault continues, replace FQGC.
- Do close out.
