Fuel Contamination

Contaminated fuel is the fuel system's common-cause failure: both engines drink from the same uplift, so what sickens one is already inside the other. The procedure's two pillars follow directly — never let the sick fuel cross the aircraft (crossfeed prohibited), and fly thrust gently and asymmetrically in time (never both levers at once). This article covers the recognition logic, the confirmed-contamination flight profile with its N1 table, and the fuel-configuration rows of the ECAM alert.

1. Recognition — two doors in

Contamination announces itself through engine-control symptoms, and the discriminator is built into the drill:

door ①: ENG 1(2) CTL SYS FAULT (with AVOID RAPID THR CHANGES
        or ENG SLOW RESPONSE) + BOTH engines' EPR fluctuating
        rapidly and continuously:
   A/THR ..................... OFF
   ├─ fluctuations STOP on both → not contamination:
   │     ECAM procedure applies · keep A/THR off
   └─ fluctuations CONTINUE on both → CONTAMINATION CONFIRMED

door ②: ENG 1 and ENG 2 CTL SYS FAULT simultaneously
        (with the messages above):
   A/THR OFF → CONTAMINATION CONFIRMED

The logic of the A/THR test: autothrust commands can themselves produce oscillating EPR. Take the commander out of the loop — if the engines still surge and sag on frozen levers, the disturbance is in the fuel. And the simultaneity test is the common-cause signature: independent failures do not strike both engines in the same minute; a shared tank does.

2. Confirmed — the gentle-thrust profile

LAND ASAP
A/THR ................... KEEP OFF
MAN THR (1st affected engine) ... SET and MAINTAIN — until final approach
   N1 by gross weight:
   GW (t):  120   130   140   150   160   170   180   190   200   210   220   230   240
   N1 (%): 58.1  58.7  59.4  60.1  60.8  61.6  62.5  63.3  64.1  65.0  65.9  66.8  67.7
cruise:   MAN THR (other engine) ........ SET AS RQRD · MINIMIZE THRUST CHANGES
descent:  MAN THR (other engine) ........ IDLE · SPD BRK AS RQRD
          level off ≈3 000 ft AGL, ≈20 NM from the threshold
landing:  resume normal SOP · FLAP LVR FULL
          configured: too fast → adjust the FIRST (set) engine
                      below VAPP trend → adjust the OTHER engine

The shape of the profile: one engine is parked at a table N1 that will fly the approach, and never touched again until final; the other engine does all the manoeuvring. Contaminated fuel makes every thrust change a gamble — so the procedure spends only one engine's gamble at a time, and keeps a known-good thrust setting banked on the other. The early level-off (3 000 ft / 20 NM) converts a normal descent into a long, stable, shallow energy problem in which big thrust changes are never needed.

3. The ECAM rows — quarantine configuration

The ENG FUEL CONTAMINATED alert's fuel-system rows build the quarantine:

on ground:  THR LEVERS IDLE              ← reject the takeoff problem entirely
in flight:  WING X FEED ... OFF / DO NOT OPEN   ← each engine drinks its own tank;
                                                  never give the contamination
                                                  a path to the second engine
            (six-tank rows:)
            L + R CTR PUMP ......... OFF  ┐ the centre tank is the prime
            trim & centre not empty:      │ suspect (one uplift, one tank);
            T TANK MODE ............ FWD  │ stop serving it, route trim
            CTR TK UNUSABLE              ┘ fuel around it — and write the
                                            centre quantity off the books
            A/THR DO NOT USE · AVOID RAPID THR CHANGES
            MOVE THR LEVERS ONE BY ONE   ← one stable engine at all times

The fuel-planning consequence is explicit: with the centre tank declared unusable, usable fuel = wing fuel — the FOB carries the half-box (controls and ECAM) and the diversion arithmetic shrinks accordingly.

One more call that costs nothing and saves the fleet's evening: tell dispatch — the same uplift batch is probably in sister aircraft's tanks right now. A contamination event is an operational alert, not just a cockpit problem. (Common-cause framing integrative; procedure rows verbatim.)

Self-test

[!note]- Q1. Why is A/THR OFF the first diagnostic step? To remove autothrust as the cause of the EPR oscillations. Frozen levers + continuing fluctuations on both engines = the disturbance is in the fuel, not the commands.

[!note]- Q2. What makes simultaneous dual ENG CTL SYS FAULT so diagnostic? Independent failures rarely strike both engines together; a shared fuel source does. Simultaneity is the common-cause signature.

[!note]- Q3. Describe the two engines' division of labour after confirmation. One engine set to the GW-table N1 and left alone until final approach (the banked, stable thrust); the other does all manoeuvring — idle in descent, adjustments on approach. Only one gamble at a time.

[!note]- Q4. Why does the crossfeed prohibition outrank even fuel-balance concerns here? Opening it would feed the suspect fuel to the engine still running well — converting a one-engine risk into a both-engines certainty. Quarantine beats tidiness.

[!note]- Q5. After the six-tank ECAM rows are complete, what is your usable fuel? Wing fuel only — the centre tank is declared unusable (its pumps off, trim fuel rerouted), and planning runs on FOB minus the centre quantity.

Key takeaways

Point	Value
Signature	both engines, same symptoms, same time — common cause
Discriminator	A/THR OFF: oscillation stops = control issue; continues = fuel
Profile	one engine parked at table N1 (58.1–67.7 % by GW), the other manoeuvres
Descent	other engine idle; level ≈3 000 ft AGL / 20 NM out
Quarantine	X FEED never; centre pumps off; CTR TK UNUSABLE; levers one by one
Beyond the cockpit	notify dispatch — the batch is in other aircraft

References

QRH engine fuel system contamination procedure (recognition doors, N1 table, profile) and FCOM PRO-ABN ENG FUEL CONTAMINATED (fuel-configuration rows).
The quarantine and one-gamble framings are integrative synthesis of the cited rows.

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.