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I'm new here and I'm in training course for Airbus A320. In the training material, it's said that the centre tank pumps are controlled to stop automatically 5 mins after the low level fuel has been reached. Why do they need to wait for a certain amount of time rather than stop right away?

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  • $\begingroup$ I'm guessing some maneuver, like a climbing turn may uncover the pick-up but there actually be fuel in the tank. $\endgroup$ – Ron Beyer Dec 1 '18 at 16:23
  • $\begingroup$ Are they electric pumps or ejectors that run on engine motive flow? $\endgroup$ – John K Dec 2 '18 at 5:04
  • $\begingroup$ On A320, they are electric pumps and they are jet pumps on A321. Thanks @Ron. Does it means the centre tank is not divided into small sections, like the wing tanks have inner and outer cells, to stop fuel movement when aircraft maneuvers? $\endgroup$ – dingdingdong Dec 2 '18 at 14:41
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To elaborate on Ron's commment, the pumps are timed because the when the level of the center tank is depleted to the minimum level that can be sensed by a low level sensor, there is usually still residual fuel sloshing around that the pump is able to draw. For both electric pumps and ejectors, you don't want them sucking air for extended periods, so you want to be able to fully deplete the tank without having the pumps run too long un-ported.

Airbus would have done testing to establish the average time to suck the tank completely dry, added a margin of some sort, then added the timer to the low level shutoff signal with the appropriate delay to achieve that end.

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  • $\begingroup$ Thanks @John :) $\endgroup$ – dingdingdong Dec 2 '18 at 23:06

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