REFUELING grounding / bonding requirements?

[1jz]

Can any one cite company procedures and regulator requirements for 3 point connections for refueling. Aircraft to refueling truck, refueling truck and aircraft both to common ground point??

[Goldenrivett]

Hi,

These poor ICAO chaps had to go all the way to Trinidad & Tobago, 9-13 JUN 2014 to discuss that sort of problem.
Slide 49 suggests that "Grounding" is not permitted.
icao.int/NACC/Doc (http://www.icao.int/NACC/Documents/Meetings/2014/GREPECASF1/GREPECASF1-2-2.pdf?Mobile=1&Source=%2FNACC%2F_layouts%2Fmobile%2Fview.aspx%3FList%3D9310 84ce-4909-478e-8b83-c0c4eefe164c%26View%3D50ea6023-006c-4af3-915c-8145e44b2994%26RootFolder%3D%252FNACC%252FDocuments%252FMeet ings%252F2014%252FGREPECASF1%26CurrentPage%3D1)

"NFPA 407, 5.4 – Bonding.
5.4.1 Prior to making any fueling connection to the aircraft, the fueling equipment shall be bonded to the aircraft by use of a cable, thus providing a conductive path to equalize the potential between the fueling equipment and the aircraft. The bond shall be maintained until fueling connections have been removed, thus allowing separated charges that could be generated during the fueling operation to reunite.
Grounding during aircraft fueling shall not be permitted."

[bvcu]

a/c grounding is not usually done these days on airliners as done through the tyres due to the compounds used these days. refuel truck is bonded to a/c though. you'd be hard pressed to find a bonding lead and ground point at an airport these days !

[ShyTorque]

Goldenrivett,

I think they mean that the actual bonding connection should not be made once refuelling has begun. Presumably the concern is that a spark could be induced at the point of connection if a static charge has built up.

[FLEXPWR]

Well, in the document mentioned, there is a clear difference between grounding and bonding. Bonding refers to various items connected together, while grounding specifies a connection made with the ground. There are several pictures in the document to illustrate this.

As for the refueling truck, it is usually grounded (often along the refueling line to the underground tank) AND bonded to the aircraft. The wording can be indeed misleading in the presentation, but one can expect that a typical refueling truck shall not try to ground while refuelling, as often the grounding connection is only centimeters aways from the ground fuel connector. This could meet a nasty end.

I am still surprised to see how many refueling operators are removing the bonding/grounding leads at the end of the refueling, before the refuel hose is disconnected. Although I do understand that any difference in potential should have leveled out, there is still a small risk. Lack of training or disregarding the rules to save a few seconds?

[EEngr]

I am still surprised to see how many refueling operators are removing the bonding/grounding leads at the end of the refueling, before the refuel hose is disconnected. Although I do understand that any difference in potential should have leveled out, there is still a small risk. Lack of training or disregarding the rules to save a few seconds? This is a good point to bring up. And static charge associated with petrochemical handling is a complex issue.

For those who think a single momentary discharge is sufficient to equalize static charges, read up on dielectric absorption (Dielectric absorption - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Dielectric_absorption)). And keep in mind that petrochemicals (i.e. fuel) make excellent dielectrics for charge storage. After disconnecting the ground lead, it is possible that a voltage differential can build up again between conductive parts (airplane and bowser tanks).

[EEngr]

Grounding during aircraft fueling shall not be permitted.There are two ways to read this statement:

Grounding as in the act of establishing a ground connection. That's a bad idea. As ShyTorque (http://www.pprune.org/members/23551-shytorque) pointed out, a built-up charge can jump at the point of connection and result in an arc. The sudden movement of charge can cause arcs at high resistance points other than the one where the connection is being established. Think of a loop between the bonding cable, aircraft, fuel truck and hoses. Connecting that cable could cause an arc somewhere else in that loop.

The other meaning of grounding is the state of being connected to the airport ground grid. Although unlikely, in the event of a fault somewhere else in the airport electrical system, currents will flow through all paths to return to the source. And if an aircraft is connected to that grid, it too might become a path for part of that current. Normal bonding assures that, while the ground grid voltage will rise, two adjacent points will remain at similar potentials and no harm or injury will occur. This is how aircraft survive lightning strikes. But if the connection is temporary and weak, the flow of fault current could result in an arc. So it would be better to keep all equipment involved in a fueling operation bonded together but isolated from other electrical sources.

[grounded27]

Technically to my knowledge as the FAA views it, the aircraft should be grounded then for fueling purposes the fuel truck should be grounded to an approved point on the aircraft (usually MLG). Normal ops as said above is to ground the fuel truck to the aircraft, many gates do not have a ground point for the aircraft.

[EEngr]

ground the fuel truck to the aircraft,

Being a bit pedantic, that would be called bonding.

Grounding would be a connection (bonding) of the aircraft to the electrical supply grounding system. Although there may not be dedicated grounding points at gates and other facilities, plugging the aircraft in to a fixed ground power source establishes such a connection.