FUEL AND ENGINE INDICATIONS NEED A TREND AND A MECHANISM
Routine fuel monitoring establishes the reference needed to recognise a developing problem. Compare remaining fuel plus fuel used with the departure quantity, and compare actual fuel at the same route point with the plan. Explain legitimate differences such as route, level or wind changes before dismissing an unexplained trend. An imbalance is a symptom with several possible causes. The FCTM explicitly requires considering a leak when unexpected quantity, fuel messages or imbalance appear. The professional question is what mechanism could produce the observations, and what information would distinguish it from another case. [21, PDF pp. 243–244] [21, PDF p. 135]
Do not turn fuel balancing into a routine response before assessing a possible leak. The source highlights a particular interaction after engine failure: where damage is suspected or apparent, crossfeed use must account for the leak assessment. This illustrates why a normally useful system action can have a different consequence under another failure mechanism. Use the applicable procedure to determine the action and preserve the sequence. This chapter does not provide a replacement leak-isolation checklist or assume that all fuel-transfer arrangements in the family are identical. [21, PDF pp. 243–244] [72, Fuel-system architecture and variant applicability]
Interpret engine indications together. Loss of thrust, a flameout, damage, a fire warning and an unsuccessful start are different initial conditions. N1/EPR, N2, EGT, fuel flow, oil information and vibration can contribute evidence, but no isolated attractive number settles the diagnosis. Apply the corresponding installed engine procedure and crosscheck significant controls before action. The surviving or restarting engine's electrical, bleed and hydraulic consequences must also be considered. The same ENG FAIL title can sit within a broader aircraft situation that determines urgency and the suitability of the next approach. [21, PDF pp. 221–228] [54, Powerplant controls and indications; CFM reference applicability]
After an engine problem or unexplained fuel trend, reassess range and landing options using the updated flight and aircraft state. Include the remaining climb capability, weather, approach and stopping performance, fuel available to the usable supply path and any system limitations. A total fuel indication does not by itself establish the amount available through a particular feed arrangement. Consult the actual fuel architecture for the selected A320-family member, including any A321 transfer/ACT installation, while keeping the diversion decision tied to the information and procedure currently available. [21, PDF pp. 243–244] [21, PDF pp. 209–213] [52, A321 Additional Centre Tanks and family configuration]
For training, separate a single engine failure, a detected fuel imbalance and a specified leak case into distinct exercises before combining them. Record the injected condition, time, fuel quantities, engine indications, routing and significant system selections. Compare the resulting trend with the predicted mechanism. If the simulation does not reproduce a particular physical leak path or subsequent branch, record that limitation rather than fabricating a successful checklist outcome. The documented failures interface establishes available selections; it does not independently verify the completeness of every simulated consequence. [127, Manual failure selection and armed/failed-state review] [21, PDF pp. 243–244]