Fuel Faults — FUEL FILTER CLOG → FUEL CONTAMINATED, the FUEL LEAK Boundary
Fuel System gave the LP/HP pumps → FMU → nozzles (with the fuel filters); 17 gave CTL SYS FAULT. This article closes the fuel-side faults: how a FILTER CLOG escalates to FUEL CONTAMINATED, and where FUEL LEAK belongs (ATA 28).
1. The clog-escalation chain
single clog: ENG 1(2) FUEL FILTER CLOG
│ escalates (10 s later) to ENG FUEL CONTAMINATED when:
├─ ① both fuel filters clogged (both FUEL FILTER CLOG), or
└─ ② both engines CTL SYS FAULT + SLOW RESPONSE (FMV failure, [17](./ata-70-17-eng-ctl-sys-fault.md))
2. FUEL CONTAMINATED — two triggers
The ENG FUEL CONTAMINATED alert triggers 10 s after the following combination of alerts: ‐ Both fuel filters are detected clogged (ENG 1(2) FUEL FILTER CLOG alerts), or ‐ Both ENG 1 CTL SYS FAULT and ENG 2 CTL SYS FAULT alerts associated with ENG 1(2) SLOW RESPONSE in the case of FMV failure. Note: The combination of both ENG 1(2) FUEL FILTER CLOG alerts is inhibited as soon as the ENG FUEL CONTAMINATED triggers.
Per PRO-ABN-ENG, ENG FUEL CONTAMINATED triggers 10 s after either ① both fuel filters clogged or ② both engines' CTL SYS FAULT + SLOW RESPONSE (FMV failure). Once it triggers, the both-FUEL-FILTER-CLOG combination is inhibited.
[!note]- Why both paths point to "fuel contamination" (synthesis) ① Both filters clogging together = a common contaminant in the fuel (dirty fuel); ② both engines CTL SYS FAULT + SLOW RESPONSE (FMV failure) = the FMVs sticking on dirty fuel (17). Both are different expressions of "fuel contamination" → merged into the FUEL CONTAMINATED alert. Inhibiting the both-CLOG combination afterwards avoids a duplicate warning.
3. FUEL FILTER CLOG (single)
ENG 1(2) FUEL FILTER CLOG = high differential across a single fuel filter (04's filters + 10's ENG SD FUEL FILTER CLOG). A single clog is an early sign; both clogged escalate to FUEL CONTAMINATED.
4. FUEL LEAK — the cross-chapter boundary
Engine FUEL LEAK monitoring and handling sits mainly in ATA 28 (abnormal quantity decrease / leak detection). On the engine side: if a leak is accompanied by fire → the ENG FIRE pb closes the LP fuel valve (12 8 actions); shutdown isolation is by ENG MASTER OFF (04). The leak-detection criteria belong to ATA 28 and are not expanded here.
5. Reading and counterintuitive point
| Alert | Meaning | Handling |
|---|---|---|
| ENG FUEL FILTER CLOG (single) | high single-filter differential | monitor (early sign) |
| ENG FUEL CONTAMINATED | both filters clogged or both CTL SYS FAULT + SLOW RESPONSE | fuel contamination (PRO-ABN-ENG) |
| FUEL LEAK | fuel leak | → ATA 28; with fire → ENG FIRE |
[!warning]- Both engines' CTL SYS FAULT + SLOW RESPONSE also points to "fuel contamination" FUEL CONTAMINATED comes not only from both filters clogged — both engines' CTL SYS FAULT + SLOW RESPONSE (FMV failure) also triggers it (PRO-ABN-ENG), because dirty fuel can stick both FMVs (17). A single CTL SYS FAULT is usually transient; both engines together is the fuel-contamination common-cause signal.
Self-test
[!note]- Q1. The two FUEL CONTAMINATED triggers, and the delay? ① Both fuel filters clogged, or ② both engines CTL SYS FAULT + SLOW RESPONSE (FMV failure), triggering 10 s later.
[!note]- Q2. What happens to the both-FILTER-CLOG combination after FUEL CONTAMINATED triggers? It is inhibited — avoiding a duplicate warning.
[!note]- Q3. Why do both engines' CTL SYS FAULT point to fuel contamination? Dirty fuel can stick both FMVs → both engines CTL SYS FAULT + SLOW RESPONSE (FMV failure), a common cause.
[!note]- Q4. Where is engine FUEL LEAK handled? Mainly ATA 28; with fire → ENG FIRE (12/ATA 26); shutdown isolation ENG MASTER OFF (04).
Key takeaways
| Point | Detail |
|---|---|
| Escalation | FILTER CLOG (single) → both clogged or both CTL SYS FAULT + SLOW RESPONSE → FUEL CONTAMINATED (10 s) |
| After trigger | both-FILTER-CLOG combination inhibited |
| Both CTL SYS FAULT | fuel-contamination common cause (dirty fuel sticks FMVs) |
| FUEL LEAK | → ATA 28; with fire → ENG FIRE |
References
- FCOM PRO-ABN-ENG — FUEL CONTAMINATED two triggers (both filters clogged / both CTL SYS FAULT + SLOW RESPONSE, 10 s) + inhibition of the both-FILTER-CLOG combination after trigger.
- FCOM DSC-70-100 / PRO-ABN-ENG (17) — CTL SYS FAULT + SLOW RESPONSE (FMV failure) link.
- Cross-chapter ATA 28 fuel / ATA 26 fire (12) — FUEL LEAK main body / fire accompaniment.
Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.