Why shouldn't we jettison fuel while flaps are in transit?

[killairbus 3]

Why can't we do it between flaps 1 and 5 but everything else is fine? Does the leading edge somehow affect fuel dumping?

 

-Angelo Busato

[YMMB 234]

I believe its because of the possibility of fuel coming in contact with the wings trailing edge and in general during fuel dumping no fuel is allowed to come in contact with any part of the aircraft.

[berts 97]

33 minutes ago, YMMB said:

I believe its because of the possibility of fuel coming in contact with the wings trailing edge and in general during fuel dumping no fuel is allowed to come in contact with any part of the aircraft.

You are correct about the risk of fuel contacting the wing trailing edge, although the risk of this happening is greatest when the Leading Edge Flaps are in transit, so strictly speaking you must not extend or retract the flaps between 1 and 5 during fuel jettison.  Provided they are not being moved from Flaps1 or Flaps5 then the risk of this happening during fuel jettison is minimal.

Edited December 9, 2018 by berts
additional information

[killairbus 3]

11 hours ago, berts said:

You are correct about the risk of fuel contacting the wing trailing edge, although the risk of this happening is greatest when the Leading Edge Flaps are in transit, so strictly speaking you must not extend or retract the flaps between 1 and 5 during fuel jettison.  Provided they are not being moved from Flaps1 or Flaps5 then the risk of this happening during fuel jettison is minimal.

So how can fuel that's jettisoned at the trailing edge, come into contact with the leading edge?

 

-Angelo Busato

[19dcavscout 39]

1 hour ago, killairbus said:

So how can fuel that's jettisoned at the trailing edge, come into contact with the leading edge?

 

-Angelo Busato

It is not so much that the fuel will come in contact with the leading edge, but that the slats at the leading will change the airflow which will allow the fuel coming out to contact the trailing edge. Hope that makes sense.

[Jetlinker 13]

Berts is correct. To further clarify it’s the outer LE devices that cause this as they are located in front of the jettison nozzles. That’s why its transiting flaps 1-5 that causes the issue, as that is the only LE flap group that moves between those settings. 

Edited December 9, 2018 by Jetlinker