The A320 fuel system stores, transfers, and delivers fuel to the engines. It consists of three main fuel tanks (left wing, center, right wing), six fuel pumps, crossfeed capability, and automatic transfer logic. Understanding tank configuration, pump operation, crossfeed valve logic, and fuel imbalance limits is essential for A320 type rating exams and daily operations.
Fuel Tank Configuration
The A320 has three main fuel tanks plus collector and surge tanks:
Left Wing Tank
Capacity: ~8,770 liters (outer wing tank). Feeds engine 1 via two fuel pumps. Contains one collector tank.
Center Tank
Capacity: ~6,476 liters (fuselage center section). Transfers to wing tanks via two pumps. Used first, empties before wing tanks.
Right Wing Tank
Capacity: ~8,770 liters (outer wing tank). Feeds engine 2 via two fuel pumps. Contains one collector tank.
Total Capacity
Standard A320: ~24,210 liters (6,400 US gal). A320neo with aux tanks: up to 27,200 liters for extended range.
Collector Tanks
Each wing tank contains a collector tank (small reservoir inside main tank):
- Located at lowest point of wing tank
- Always contains fuel even when main tank nearly empty
- Fuel pumps are submerged in collector tanks
- Prevents fuel pump cavitation and air ingestion
- Ensures continuous fuel supply during maneuvers (pitch/bank)
Surge Tanks
Wing tip surge tanks accommodate fuel expansion and prevent overflow:
- Located at wing tips (highest point)
- Collect fuel expansion due to temperature increase or descents
- Fuel drains back to main wing tank via vent system
- Not counted in usable fuel quantity
Fuel Pumps
A320 has six fuel pumps total - two per tank:
| Tank | Pumps | Function | Control |
|---|---|---|---|
| Left Wing | 2 pumps | Supply fuel to ENG 1 (or both engines via crossfeed) | L TK 1 and L TK 2 pump switches |
| Center Tank | 2 pumps | Transfer fuel to wing tanks (not directly to engines) | CTR TK 1 and CTR TK 2 pump switches |
| Right Wing | 2 pumps | Supply fuel to ENG 2 (or both engines via crossfeed) | R TK 1 and R TK 2 pump switches |
Pump Operation
- Normal Operations: All wing tank pumps ON, center tank pumps ON when center tank has fuel
- Redundancy: Each engine can run on single pump from its respective wing tank
- Gravity Feed: If all pumps fail, engines can gravity feed from wing tanks (reduced flow, altitude limited)
- Automatic Shutoff: Center tank pumps automatically stop when center tank quantity drops below ~250 kg
⚙️ Fuel Pump Pressure
Each fuel pump provides approximately 3.8-4.0 bar pressure. Normal fuel pressure to engines: 3.5-4.0 bar. LOW FUEL PRESSURE warning triggers if pressure drops below ~2.5 bar. Single pump per wing is sufficient for normal operations, but both are normally used for redundancy. Center tank pumps have higher pressure (~6 bar) to overcome wing tank pressure and transfer fuel.
Crossfeed System
The crossfeed valve allows fuel transfer between left and right fuel manifolds, enabling either engine to receive fuel from either wing tank.
Crossfeed Valve Operation
- Normal (crossfeed closed): Each engine feeds from its respective wing tank only (ENG 1 from left, ENG 2 from right)
- Crossfeed OPEN: Fuel manifolds interconnected, either engine can draw from either tank
- Control: X FEED pushbutton on fuel panel (guarded)
- Indication: OPEN light illuminates when valve open
Crossfeed Usage Scenarios
| Scenario | Procedure | Reason |
|---|---|---|
| APU Start on Ground | Open crossfeed if APU fuel from opposite tank desired | Fuel APU from tank with more fuel |
| Engine Start Imbalance | Open crossfeed, start both engines from one tank | Prevent further imbalance during start |
| Fuel Imbalance Correction | Open crossfeed, feed both engines from heavy wing | Reduce imbalance by consuming fuel from heavy side |
| Single Fuel Pump Operation | May open crossfeed depending on procedure | Ensure adequate fuel supply to engines |
| Fuel Leak from One Wing | Open crossfeed, feed both engines from good tank | Preserve fuel in leaking tank, maximize range |
⚠️ Crossfeed Limitations
• Do NOT open crossfeed with fuel imbalance > 370 kg (structural limits)
• Close crossfeed before landing (unless required by abnormal procedure)
• Monitor fuel flow to ensure both engines receiving fuel when crossfeed open
• If engine fire occurs with crossfeed open, close crossfeed immediately to isolate fuel
Center Tank Transfer Logic
Center tank fuel transfers automatically to wing tanks, ensuring center tank empties before wing tanks.
Transfer Sequence
- Before Flight: If using center tank fuel, ensure center tank pumps ON
- After Takeoff: Engines consume fuel from wing tanks, wing tank levels decrease
- Transfer Starts: When wing tank quantity drops to preset level (~5,000 kg per wing), center tank pumps activate
- Center to Wings: Center tank pumps transfer fuel into wing tanks at higher pressure than wing pumps
- Transfer Complete: When center tank quantity < 250 kg, center tank pumps automatically switch OFF
- Remainder of Flight: Engines consume from wing tanks only
🔄 Why Center Tank Transfers to Wings?
Center tank does NOT feed engines directly. It transfers to wing tanks first because:
• Wing tanks contain fuel pumps in collector tanks that guarantee continuous supply
• Center tank location makes direct engine feed difficult (long fuel lines, gravity issues)
• Transfer ensures center tank (difficult to empty completely) used first
• Wing tanks maintained at adequate level for aircraft balance and structural limits
Center Tank Pump Indications
- Pumps ON, CTR TK > 250 kg: Pumps operating, fuel transferring
- Pumps ON, CTR TK < 250 kg: FAULT light illuminates, pumps stop (normal when empty)
- Pumps OFF: No transfer, center tank fuel not used
Fuel Imbalance
Fuel imbalance occurs when left and right wing tanks have significantly different fuel quantities.
Imbalance Limits
| Condition | Limit | Action |
|---|---|---|
| Normal Operations | < 370 kg | No action required, monitor |
| ECAM Caution | > 370 kg | F/CTL FUEL IMBALANCE caution triggers |
| Correction Required | > 370 kg | Follow ECAM procedure to balance fuel |
| Structural Limit | 740 kg | Maximum allowable imbalance (structural) |
Imbalance Correction
To correct fuel imbalance > 370 kg:
- Open crossfeed valve (X FEED pb ON)
- Turn OFF fuel pumps on heavy wing tank
- Both engines now feed from light wing tank only
- Heavy wing tank accumulates center tank transfer (if center tank active) or simply remains unused
- When imbalance reduced to acceptable level, close crossfeed and restore normal pump configuration
🚨 Fuel Imbalance Causes
Common causes of fuel imbalance:
• Fuel leak from one wing tank
• Failed fuel pump on one side (single-pump operation consuming asymmetrically)
• Unbalanced fuel loading on ground
• Engine fuel consumption difference (engine degradation, bleed configuration)
• Crossfeed left open during normal ops
If imbalance develops rapidly or unexpectedly, suspect fuel leak and follow ECAM procedures carefully.
Gravity Feed
If all fuel pumps fail on one or both sides, engines can gravity feed from wing tanks.
Gravity Feed Characteristics
- Fuel Source: Wing tanks only (center tank cannot gravity feed)
- Altitude Limitation: Gravity feed typically limited to lower altitudes (~FL 200 or below, depends on fuel quantity)
- Reduced Flow: No pump pressure, fuel flows by gravity alone
- Engine Operation: Engine can run normally at reduced altitude with adequate fuel quantity
- Performance: Plan to descend and land at nearest suitable airport
⚠️ Gravity Feed Limitations
Gravity feed is emergency capability only:
• Maximum altitude decreases as fuel quantity decreases
• High altitude flight not possible
• Negative G maneuvers may interrupt fuel flow
• Descent and landing as soon as practical
• Crossfeed may be used to feed both engines from one tank
Fuel Temperature
Fuel temperature monitored to prevent ice crystal formation or freezing:
- Minimum Fuel Temp: -43°C (Jet A-1 freeze point -47°C, margin required)
- Indication: ECAM advisory if fuel temperature approaches minimum
- Corrective Action: Descend to warmer altitude or increase speed (fuel heats from engine return flow and friction)
Refueling and Defueling
Refueling Panel
Located under right wing, used for ground refueling:
- Tank selection and quantity management
- Refuel rate control
- Automatic shutoff when tanks reach desired quantity
Fuel Loading Strategy
- Wing Tanks: Always load wing tanks (required for flight)
- Center Tank: Only load if total fuel required > wing tank capacity (~17,000 kg)
- Balance: Load left and right wings equally (imbalance < 370 kg)
- Trim Fuel: Some operators use slightly unbalanced fuel for cruise trim optimization (within limits)
Frequently Asked Questions
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