Old not Bold
Its quite common to have that restriction on re-use defuelling.
Aircraft fuel is subject to a chain of custody type arrangement and is incredibly well tested, inspected and certified, even though each batch is slightly different because of small variations in its distillation charateristics, the refinery it came from and the processes employed there (eg in catlytic cracking, Sulphur removal etc.), and the crude it was distilled from. Even the minute amounts of water and sediment it picked up during distribution is removed just before final storage and the quality and water content is spot tested yet again at the hydrant servicer before going into the wing.
The simple answer is that you break that chain of custody and inspection by putting it in your dirty old aircraft and taking it out again and you just dont know what you have got, in terms of contaminants, fungus, sediment, water, etc. etc. Aircraft operating in tropical environments and subject to high relative humidity, heating/cooling cycles etc. frequently experience microbial growth which is treated using special additives eg Biobor JF or others. But there's no easy on-site spot test for these additives and anything other than the basic contaminants, so you really have no idea what you might get UNLESS its one of your own company fleet in which case you will have the assurance (you hope!) that the overfuelled aircraft was fuelled according to your own policy and you and your insurers would be a bit more relaxed about taking it.
The other thing that makes it a pain is that while large aircraft are commonly fuelled under pressure from a 'hot hydrant system' which is kept pressurised and is set into the apron, the reverse process is not possible. So it usually has to be discharged into a bowser (like you would use for smaller aircraft or with AVGAS) and there you have another point of contamination, need to inspect, certify, etc etc. Its a dogs breakfast, a lot of extra work, huge amounts of implied risk, and its easier just to dump it into power kerosene. because the spec is usually the same (except that Jet has a restriction on freeze point, power or heating paraffin/kerosene has a restriction on smoke point).
Pinkman
Last edited by Pinkman; 8th Aug 2007 at 14:10.
Reason: pore spelin