A320 Maximum Fuel Temperature
 

Just another one of those Airbus "You Figure This Out" situations...

Regarding the FUEL TEMPERATURE INDICATION on the A320, on the FCOM 1.28.20 P10 it is mentioned that:"It becomes amber, and ECAM displays a caution, if the temperature goes above the high limit or below the low limit".

Furthermore, on FCOM 1.28.20 P12, in the Warnings and Caution list it further states that the failure title and conditions are:
"L(R) OUTER TK HI TEMP or L(R) INNER TK HI TEMP Fuel temp above:
in outer cell above 60°
in inner cell above 54°".
So far so good, so one reasons that these stated temperatures are the high limits.

Why then would on FCOM 3.02.28 FUEL L (R) OUTER (INNER) TK HI TEMP the temperatures referred be "If TEMP ABV 65 DEC C in outer cell or 57 DEG in inner cell" ?

If the ECAM is triggered that means that something is wrong. Isn't it being a little too precious to be waiting for the temperature to further increase 5° in the outer cell and 3° in the inner cell respectively to start the APU and disconnect the IDG? It just doesn't make sense or am I missing something? So are the 60° and 54° temps just limits to trigger the Master Caution but not the actual temperature limits? It's a minor detail really, but does anyone have a clue on this?

Ayayay caramba, Airbus, ..... You make me loco!

ITs like most things on the aircraft...wouldnt you like a kind of warning first before an impending failure (if thats the case)?? No point in telling you that you have now hit the limit, nothing you can do now! Its telling you there is an impending situation, yet following whatever procedures you have time to try corrective action to avert this situation.
It is like when you get a Fuel Filter Clog msg....its not telling you the filter is actually clogged, but, if you continue as you are it will clog. (e.g. icing conditions in the fuel may be present, thus possibly causing filter to clog or whatever other reason may be the case)

C. Temperature Sensors
The tank level sensing system has two temperature sensors, 29QJ1 (29QJ2)
and 30QJ1 (30QJ2), installed in each wing tank. The temperature sensor
29QJ1 (29QJ2) is in the wing tank inner cell and is sensitive to
temperatures of more than 52.5 deg C. The temperature sensor 30QJ1
(30QJ2) is in the wing tank outer cell and is sensitive to temperatures
of more than 55 deg C.
Each temperature sensor is near the lowest part of the related fuel cell.
This makes sure that the temperature sensor is in the fuel for most of
the time.
Do NOT confuse these with the sensor which activates the IDG NRT..

airbusbatics,

Good questions!

The Aircraft Operating Manual that I use has slightly different
limits than the ones you quote, but for the moment let's disregard
that.

The Fuel Tank High Temperature 'caution' comes on when certain
actions need to be taken in an attempt to reduce the temperature of
the fuel. Some of these actions are positive and some are conditional.

For the A319/A320 there is a caution that states "This caution may
spuriously trigger due to interference from the communications
equipment. Therefore the flight crew should wait two minutes while
the fuel temperature is updated. After two minutes, if the ECAM
caution has not disappeared, the flight crew must apply the following
procedure." The A321 does not have that caution.

On all models the ECAM starts off with a positive action. The GALLEY
power supply is turned off in an attempt to reduce the generator
loads thereby reducing the heat emitted by the offending IDG and
thereby reducing the temperature of the fuel returning to the tanks.

The expanded ECAM then offers a conditional statement ... "on the
ground" or "in flight". Let's deal with the "in flight" situation as
it has the potential to be more serious.

On all models the first action is to disconnect the autothrust and
adjust the thrust lever to increase the fuel flow through the IDG oil
heat exchanger and decrease the temperature of the fuel returning to
the outer cell (A319/A320) or the wing tank (A321).

The second step is conditional and is actioned if the fuel temperature
rises above 65c in the outer cell, or 57c in the inner cell in the
A319/A320 or above 57c in the wing tank of the A321. That step is to
start the APU, if available, so as to allow the IDG on the affected
side to be disconnected.

The third step, which is also conditional, is to disconnect the
affected side IDG, but only if the opposite generator is available.

The first caution comes on at the lower temperatures to alert you
that certain items need to be accomplished in an attempt to keep the
fuel temperature from rising over the next limit which requires even
more action.

If the first actions are successful then the later actions will not
have to be accomplished. And please note the conditonal statement
regarding the diconnectiong of the offending IDG ... the opposite
generator must be available. Airbus always wants you on at least two
generators.

Fuel Gauge spec
 

It might simply be that the spec for the FQIS is to work within that range of temperatures, and simply a warning to treat fuel gauge readings with caution.

Brilliant answers!

Thank you all for your replies.

And as long as I have your attention, if I could further take advantage of your knowledge, I have another question here:

A320 Fuel Consumption Increase (L/G & Flaps out) - PPRuNe Forums

Also, in case of high fuel temperature (>52.5°C), IDG cooling fuel return to outer tank is automatically inhibited. The hot fuel goes to the injectors instead. But this inhibition is only effective while airborne.

Thence, I suppose, the different temperature thresholds on the ground and in the air from dealing with this abnormal.

what kind of failures will follow an increase of fuel temp if ecam is delayed?

The main engine fuel pumping system will become affected by release of entrained air and near idle (low absolute fuel pressure) by fuel vapour creation at one of the pressure steps after the HP pump - probably creating striated flow after the HP SOV. The first symptom may be noisy display of FF, in extremis, the engine will run down.
There may be other (aircraft) sub-systems affected.

Prolonged idle on near empty tanks while waiting for a stand (for example)will cause a fuel over temp.