The easyJet Airbus fleet has evolved to include a number of variations of the fuel system. The two major variations, from the point of view of non-normals, are the replacement of electrical center tank pumps with jet transfer pumps on some airframes and the simplified tank system of the A321 neo where the normal outer and inner cells are replaced with a single wing tank. In addition, some airframes are fitted with a center tank fuel inerting system, but since there are no cockpit controls for this, it doesn’t affect the non-normal procedures.
The philosophy of center tank jet transfer pumps is very different from that of the electrical pumps. With the electric pumps, fuel is supplied directly from the center tank to the engines, and any transfer between center tank and wing tank is a side effect of the fuel return system. With the jet transfer pumps, fuel is only ever transferred from the center tank to wing tanks: it is always the wing tank pumps that supply pressurised fuel to the engines. The jet transfer pumps themselves are also powered by the wing tank pumps: if there is a need to shut down a jet transfer pump, that is achieved by turning off the associated wing pumps. There also appears to be some scope for gravity feeding from the center tank when jet pumps are fitted (although 2T of center tank fuel will still be unusable),1 something that is not possible with the electrical pumps. This leads to some subtle airframe dependent differences in non-normal fuel procedures.
The simplification of the wing tanks on the A321 neo has less impact on non-normal procedures: it is mainly a case of changing ecam titles appropriately.
Whenever a non-normal fuel event occurs, the possibility that the underlying cause of the event is a fuel leak should be considered. Only when a fuel leak has been categorically ruled out should the cross-feed valve be opened.
The primary method used to detect fuel leaks is a regular check that actual fuel remaining corresponds to expected fuel remaining and that fuel used plus fuel remaining corresponds to fuel at engine start. The latter parameter is monitored on some aircraft and may trigger an ecam warning. Other indications of a leak include fuel imbalance or excessive fuel flow from an engine. It is also possible that a fuel leak may be detected visually or by a smell of fuel in the cabin.
If a leak can be confirmed to be coming from an engine or pylon, either visually or as indicated by excessive fuel flow, the affected engine must be shut down. In this case, cross-feeding is allowable. Otherwise, the cross-feed must be kept closed.
If the leak cannot be confirmed to be originating from an engine or pylon, an attempt should be made to identify the source of the leak by monitoring the inner tank (or, for A321 neo, wing tank) depletion rates with the crossfeed valve closed and the center tank pumps off.
If depletion rates are similar, a leak from the center tank or from the apu feeding line should be suspected. If there is a smell of fuel in the cabin, it is likely that the apu feeding line is at fault and the apu should be turned off. Fuel from the center tank should be used once one of the inner/wing tanks has <3000kg.2
If, after 30 minutes, one tank has been depleted by 300kg more than the other, the location of leak is narrowed down to the engine or the wing on the more depleted side. To confirm which it is, shut down the engine. If the leak then stops, an engine leak is confirmed and the cross feed can be used. If not, a leak from the wing is most likely. In this case, an engine restart should be considered.
The handling of the center tank pumps in the presence of a fuel leak is dependent on whether the aircraft is fitted with electrical center tank pumps or with jet transfer pumps. When electrical center tank pumps are on, no fuel is transferred between the center tank and the wing tank unless the engine associated with that wing tank is running. If an engine is running with electrical center tank pumps on, surplus fuel is returned from the engine to the associated wing tank, and thus a fairly modest rate of transfer occurs. The jet transfer pumps, on the other hand, transfer fuel directly from center tank to wing tank at a high rate regardless of whether the associated engine is running. It is therefore important not to run a jet transfer pump if you suspect its associated wing tank has a leak since significant extra fuel loss would likely occur.
In an emergency, a landing may be carried out with maximum fuel imbalance.
Do not use thrust reversers.
[ fuel f used/fob disagree, qrh aep.fuel, fcom pro.aep.fuel ]
All fuel balancing must be carried out in accordance with qrh fuel fuel imbalance, paying particular attention to the possibility of a fuel leak. Any action should be delayed until sufficient time has passed for a fuel leak to become apparent. The fcom adds a note not found in the qrh that “there is no requirement to correct an imbalance until the ecam fuel advisory limit is displayed”, an event that occurs when one inner tank holds >1500kg more than the other. The limitations for fuel imbalance in fcom lim.fuel, however, show that the fuel advisory does not necessarily indicate that a limitation is likely to be breached. In particular, when the outer tanks are balanced and the heavier inner tank contains ≤2250kg, there are no imbalance limitations. Furthermore, the aircraft handling is not significantly impaired even at maximum imbalance.
To balance the fuel, open the cross-feed valve and turn the lighter side pumps and the center tank pumps off.
[ qrh aep.fuel, fcom pro.aep.fuel, fcom lim.fuel ]
Turn on ignition and avoid negative G. The ceiling at which fuel can be reliably gravity fed depends on whether the fuel has had time to deaerate, this being a function of achieved altitude and time at that altitude. The algorithm used to calculate gravity feed ceiling is airframe dependent and is provided in the qrh. Once calculated, descend to the gravity feed ceiling; it may be as low as fl150, so terrain must be considered.
It is also possible to gravity cross feed by side slipping the aircraft with the cross feed valve open. The section of the qrh describing this procedure has recently (June 2017) been cleaned up by moving an explanatory note into a branch title, but this has had the effect of changing the apparent intention. Previously, gravity cross feeding was indicated when single engine and required “for aircraft handling” (i.e. it could generally be disregarded), whereas with the update the procedure is indicated whenever gravity feeding on a single engine. Clarification has been requested from Airbus via the easyJet Technical Manager, and these notes will be updated once a response is received.
[ qrh aep.fuel, fcom pro.aep.fuel ]
Failed pumps should be turned off.
Failure of a single pump in either tank results in reduced redundancy only.
Failure of both pumps in a given tank means that the fuel in that tank is only available by gravity feeding. Pressurized fuel may be available from the center tank (use manual mode if necessary) or by cross-feeding. A descent to gravity feed ceiling may be required (see Section 8.4).
[ fuel l(r) tk pump 1(2)(1+2) lo pr, fcom pro.aep.fuel ]
Failed pumps should be turned off.
Failure of a single center tank pump results in a loss of redundancy. The crossfeed should be opened until the center tank fuel has been exhausted so that the remaining pump can supply both engines.
Failure of both center tank pumps makes the fuel in the center tank unusable.
[ fuel ctr tk pump(s)(1(2)) lo pr, fcom pro.aep.fuel ]
Since the motive power for jet transfer pumps comes from their associated wing tank pumps, their main failure mode is failure of their associated center transfer valve.
If a valve fails in a not fully closed position, fuel may continue to be transferred to the wing tank even when it is full, and will thus overflow. Selecting the transfer pump off may be effective; otherwise the jet transfer pump’s motive power is removed by switching off its associated wing tank pumps, with the wing tank pumps from the unaffected side supplying both engines until the center tank is empty. If both sides fail in this way, all that can be done is to turn the center tank transfer pumps off; it may not be possible to prevent fuel overflow.
If a valve fails in a not fully open position, fuel may not be transferred between center tank and wing tank on the affected side. Manual control of the transfer pumps may be effective; if not, feeding both engines with the wing tank pumps of the unaffected side until the center tank is empty is once again the solution. If both sides fail in this way and manual control is not effective, 2T of center tank fuel are unusable; the rest is available by gravity.
[ fuel ctr l(r)(l+r) xfr fault, fcom pro.aep.fuel ]
Whenever center tank fuel is being used, fuel is transferred from the center tank to the wing tanks. In the case of jet transfer pumps this is a direct transfer; in the case of electrical pumps it is via the fuel return system. Center tank fuel can thus only be used when there is space in the wing tanks to receive this transferred fuel. The pumps therefore automatically cycle on and off, starting when there is space for 500kg in the wing tanks and stopping when the wing tanks are full, until such time as the center tank fuel is exhausted. In addition, electrical center tank pumps are inhibited whenever the slats are extended.3
Malfunction of the automatic cycling of the center tank pumps (electrical or jet transfer) is identified by the presence of more than 250kg of fuel in the center tank when there is less than 5000kg in one of the wing tanks. Malfunction of automatic control of electrical pumps is also indicated when they continue to run when slats are extended or the center tank is empty.
If the automatic control has malfunctioned, the cycling of the center tank pumps must be managed manually. For both types of pump, they should be switched on whenever one of the wing tanks has less than 5000kg fuel and center tank fuel remains, and switched off when one of the wing tanks is full or the center tank fuel is exhausted. In the case of electrical pumps, they must also be switched off whenever the slats are extended.
[ fuel auto feed(transfer) fault, fcom pro.aep.fuel ]
When center tank fuel transfers to a wing tank, either directly in the case of transfer pumps of via the fuel return system in the case of electrical pumps, and that wing tank has no space to accommodate it, that fuel will overflow.
To stop the overflow, the fuel transfer must cease. In the case of electrical center tank pumps, this is just a matter of switching the offending center tank pump off. With jet transfer pumps, switching the pump off may also be effective; if not, remove motive power of the offending pump by switching off both of its associated wing pumps – pressurised fuel will be available via crossfeed.
[ fuel l(r) wing tk overflow, fcom pro.aep.fuel ]
The ecam is triggered at approximately 750kg. This warning is generated by sensors that are independent of the fqi system. The warning may be spurious if the ecam is triggered just before the wing cell transfer valves open. If center tank fuel remains, it should be used by selecting the center tank pumps to manual mode. If there is a fuel imbalance and a fuel leak can be ruled out, crossfeed fuel as required.
If both tanks are low level, about 30 minutes of flying time remain.
If any change to the current clearance will lead to landing with less than minimum reserve fuel, declare “minimum fuel” to atc. This is just a heads up to atc, not a declaration of an emergency situation. If it is calculated that less than minimum fuel will remain after landing, declare a Mayday.
[ fuel(r)(l+r) wing tk lo lvl, fcom pro.aep.fuel, eoma 8.3.8.2 ]
Imbalances caused by the outer tank transfer valves on one side failing to sequence correctly, either by failing to open or by opening out of sequence, will not exceed limits, provided that the total fuel in each wing is the same (see fcom lim.fuel).
Of more concern is the sudden loss of usable fuel when transfer valves fail to open on schedule. If only one side is affected, 700kg of fuel will become unusable. If both sides are affected, 1400kg of fuel will become unusable. This will happen when fuel levels are already fairly low, as the valves are triggered when an inner tank reaches 750kg, potentially leaving you with just 1500kg of fuel when you were expecting to have 2900kg.
[ fuel l(r) xfr valve open, fuel l(r) xfr valve closed,
fcom pro.aep.fuel ]
If the valve has failed open, fuel balance can be maintained through selective use of fuel pumps. If it has failed closed, crossfeeding is unavailable.
[ fuel feed valve fault, fcom pro.aep.fuel ]
ecam is triggered at approx -43°C for A319/A320 and -44°C for A321. If on the ground, delay takeoff until temperatures are within limits. If in flight, descending or increasing speed should be considered.
[ fuel l(r) outer(inner) tk lo temp, fcom pro.aep.fuel ]
This ecam is known to be triggered spuriously by interference from communication equipment. The procedure should only be applied if the message has not disappeared within 2 minutes.
The ecam temperature triggers on the ground are 55°C for an outer cell and 45°C for an inner cell or A321 wing tank. In the air they are 60°C for an outer cell and 54°C for an inner cell or A321 wing tank.
The temperature of fuel returning to the tanks is primarily a function of idg cooling requirement. The immediate action, therefore is to turn the galley off to reduce the idg load.
On the ground, the engine on the affected side must be shut down if an outer cell reaches 60°C, an inner cell reaches 54°C or, for the A321, the wing tank reaches 55°C. An expeditious taxi may, therefore, be advantageous.
In the air, if only one side is affected, fuel flow can be increased so that less hot fuel is returned to the tanks. If the temperature gets too high (>65°C outer or >57°C inner/wing), idg disconnection will be required (see Section 5.3).
[ fuel l(r) outer(inner)(wing) tk hi temp, fcom pro.aep.fuel ]
1This information only appears in the fuel ctr l+r xfr fault checklist. I have requested further information and will update once I get a response.
2The logic here is strange. An unofficial explanation of the requirement for <3000kg in the inner tank was given to me: some of the fuel lines from the center tank run through the wing tanks, so fuel from a center tank leak may end up transferring to the wing tanks and with full wing tanks will be lost overboard. As for the apu feeding line leak, I would expect the left tank to decrease faster than the right in this case; my guess is that the expectation is that an apu feeding line leak will be detected as a smell in the cabin and the leak will be too small to become apparent as an imbalance.
3As always with Airbus, there is an exception. If there is fuel in the center tank, each electrical center tank pump will operate for two minutes after its associated engine is started, regardless of slat selection, to pre-pressurise the center tank fuel lines.