B744 Fuel Jettison Flaps 1 - 5
 

B747-400 'Fuel Jettison' checklist, does not allow jettison with flaps in transit between flaps 1 and flaps 5.
Does anyone know why? (I don't):O

The restriction is only whilst the flaps are in transit between 1 and 5. The reason being there is disruption of airflow over the
tail area.

My understanding is that the outboard leading edge flaps move during Flaps 1 to 5 (and 5 to 1) and their influence on the fuel stream could cause fuel to contact the trailing edge of the wing.
The jettison nozzles are outboard of the low speed ailerons near the wingtips and well away from the trailing edge flaps. Of course, the t.e. flaps are HUGE and must also influence the airflow in that area.

The result of this is that the smell of fuel enters the cabin.

Not a nice addition to whatever problem you already had that made you dump fuel.

Sorry but the only smells that enter the cabin either go down the inlet of the engines or into the inlet of the APU.
The answer is as Eckhard said the transit of the LE (group B) infront of the fuel jetteson nozzle may cause fuel to come into contact with the trailing edge.

This pic is not bad for reference.

http://www.!!!!!!!!!!!!!!/open.file/173455/L/