Fuel Temperature Faults

Fuel has a working band: too cold and it approaches its freezing point (wax crystals, clogged feed); too hot and its vapour pressure climbs toward trouble. The A330 watches both ends through the four temperature probes (MMI and fuel temperature) and answers each with a different philosophy: cold fuel gets moved to warmer tanks; hot fuel gets time and idle. This article covers both alerts and the cruise strategy behind the cold one.

1. FUEL LO TEMP — the cold end

Thresholds (first level / recall level):

The outers and trim sit at thinner, more exposed structure — they chill first and alert later (lower thresholds) because their fuel is also further from the engines' immediate needs.

First action — know your fuel:

FUEL FREEZE PT ............. CHECK

The alert thresholds are generic; the limit is your fuel's actual freezing point (JET A1: −47 °C). The procedure says so explicitly — execution of the remaining steps may be delayed until the temperature approaches the applicable limit. An alert at −37 °C with A1 aboard is early information, not an emergency.

On the ground (JET A family): delay the takeoff until temperatures recover into limits.

In flight — the three moves, all toward warmth:

inner cold (JET A):    CTR TANK XFR ........ MAN      ← blend warmer centre
                                                        fuel into the inners
outer cold (JET A):    OUTR TK XFR .......... ON      ← small cold cups into
                          (newer standard: centre        the big warmer pool;
                           pumps OFF first if centre     stop the centre topping
                           not empty)                    the outers back up
trim cold (JET A):     T TANK MODE .......... FWD     ← evacuate the coldest,
                          (trim pump failed → the        most remote fuel
                           270 kt / not-in-climb gate;   (≈1 % burn penalty;
                           CG fwd of 26 %: monitor       CG watch while it runs)
                           the CG during transfer)

The common idea: cold fuel in a small exposed tank is a liability; the same fuel blended into a large, IDG-warmed inner tank is diluted into safety. Note the newer-standard footnote on the outer move — with the centre tank still feeding, its transfer would quietly refill the outers through the gallery; the centre pumps come off first.

The strategic lever — raise TAT:

IF NECESSARY: TAT ......... INCREASE

Descend and/or accelerate. The planning numbers: roughly +7 °C per 4 000 ft of descent, +0.7 °C per 0.01 Mach — and fuel temperature lags TAT by about an hour. That lag is the operational sting: the decision must come early, while the trend is still shallow; a crew that waits for the recall threshold has spent its margin waiting. (Planning figures per the cold-fuel guidance; the lag is the reason the procedure's "may be delayed" has a deadline.)

2. FUEL L(R) INNER TK HI TEMP — the hot end

Thresholds: 45 °C on the ground / 49 °C in flight — and a grading hidden in the recall logic: the ground alert at 49 °C re-presents for action because 49 °C is the action line for JET B / JP4; at 55 °C it concerns all certified fuels (the LIM-FUEL maximums — overview).

on ground, JET B fuel:
   DELAY T.O.
   ENG MASTER (affected side) ......... OFF    ← the IDG return is the heater;
   APU ............................. AS RQRD     stop feeding it heat
in flight: crew awareness

Why the asymmetry between ground and air: on the ground the inner tanks absorb IDG cooling heat with little fuel burn to carry it away (engine feed); in cruise the TAT is low and the burn-through is high — altitude is the cure, and the alert in flight is informational. The ground cure is equally direct: shut down the engine on the hot side and let the tank cool.

Self-test

[!note]- Q1. LO TEMP triggers at −37 °C with JET A1 aboard. How urgent? Informational at that point — A1 freezes at −47 °C, and the procedure permits delaying the moves until the temperature nears the actual limit. Urgency comes from the one-hour lag, not the alert.

[!note]- Q2. Recite the three cold-fuel moves and their shared logic. Centre MAN into the inners (blend warm), outers ON into the inners (dilute the cold cups — centre pumps off first on newer standards), trim FWD out of the coldest tank. All: move cold fuel into the big warm pool.

[!note]- Q3. What do 4 000 ft and 0.01 Mach buy you, and when must you spend them? About +7 °C and +0.7 °C of TAT respectively — but fuel temperature follows with ~1 h of lag, so the descent/acceleration decision must be made early on the trend, not at the recall.

[!note]- Q4. Why is 49 °C "recallable" on the ground but only awareness in flight? 49 °C is the JET B/JP4 action line (55 °C for all fuels); on the ground the IDG return keeps heating a static tank — hence delay, engine off. In flight, cold TAT and fuel burn carry the heat away.

[!note]- Q5. Which tank's cold-fuel move carries a CG side-condition, and what is it? The trim move (T TANK MODE FWD): with the CG forward of 26 % MAC, monitor the CG during the transfer — a monitoring line, not the 32 % two-step rule (forward transfer).

Key takeaways

References

• FCOM PRO-ABN-FUEL LO TEMP / INNER TK HI TEMP (both configurations); LIM-FUEL (temperature limits, fuel types).
• FCOM cold-weather/cruise guidance (TAT planning figures and lag).
• The grading interpretation of the 49/55 °C recalls and the dilution framing are integrative synthesis.

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.