Grounding aircraft while refueling - Master OFF?

[praveen4143]

Ok, so we all understand that we should be grounding (or bonding if fueling from a fuel truck/bowser) the airplane when we fuel up. We probably also understand why we do it.

My question is, is it important that the MASTER be OFF while we fuel? Why or why not?

[mcrit]

Short answer is no; in fact most larger aircraft require power to be on for refuelling (most fuel valves are electrically operated.

The long answer is that static charge builds up in the skin and structure of both the airplane and the bowser.  If the bowser and the airplane have an unequal amount of charge a spark will jump where they touch each other.  Bonding or ground ensures that the initial spark happens away from fuel vapours and that no further difference in charge can develop.
Turning the master switch on or off does not change the overall amount of charge in the aircraft structure, so it's not going to cause a spark to jump between the bowser and the aircraft.

[Gravedigger]

That's a hell of an answer mcrit!  I like it!  We have just one simple rule in regards to filling up with the master running( APU going ).  We do not do any electrical switching during this time as well. No lights turning on or off, no pax signs etc

[praveen4143]

Awesome answer @mcrit. I was kinda thinking on similar lines, but wasn't 100% sure. Thanks!

@Gravedigger, do you mean just actual usage of the switches while fueling up, as in if it is on, leave it on, and if off, leave it off?

[Colonel]

You want to avoid both static electricity
(ie via grounding) and arcing at electrical
contacts (ie moving switches).

Sparks are bad.  Got it?

[img]http://ecx.images-amazon.com/images/I/7 ... SY355_.jpg[/img]

[Gravedigger]

Yep you got it!  If fuel is pumping just leave those switches alone!

[David MacRay]

[quote author=Gravedigger link=topic=212.msg701#msg701 date=1433930029]
Yep you got it!  If fuel is pumping just leave those switches alone!
[/quote] Because it is pushing fumes out of the tank as it fills and they are the most flammable.

[Nark1]

Not sure if I agree...

The E170/190 we flipped switches all we wanted, during fueling, however APU start or stops were forbidden.

In the Airbus, the manual says APU Start/Stop is fine.  It only prohibits start/stoping (during fueling) if there was a fault.

In the Blackhawk, and any other military bird, we hot fuel, with blades turning at 100%.  However we turn off (transmitting function) alot of our electrical gadgets, and don't transmit on the radios. 

Certainly there is some voodoo magic somewhere in the mix, why we do what we do.

[Gravedigger]

SOP's are SOP's.  For the general public I would say if your fueling its a good idea to just have everything off.  Then your safe. When fueling your car you shut off the ignition and keys out. Thus the sign with a key in a red circle with a line through it at every pump!!