I suspect that there was no visual inspection prior to refuelling, since the tech log suggested only about 1/4 tanks - which would not be visible (the AIB report doesn't mention a visual inspection, only checking the drains).
After refuelling, I suppose there was no visual inspection either - since he'd presumably seen it being fuelled with his desired amount.
Back in the cockpit, and the gauges show 4/4 and 3/4, and he thinks "gee, there must have been more fuel left over than I thought", but doesn't get out again to make a visual inspection - to what purpose? He has just seen his route fuel put in, and knows there is enough (ignoring his poor fuel planning and conversion errors) for the flight. Any extra is a bonus, and he doesn't want to bring it back with a lot of fuel - because of the local operators requirements.
Lets suppose he does get out and make a visual check, and sees the left tank is not full. What would he think? "Well, these fuel guages are notoriously inaccurate (just read this thread
) - but I have put in enough route fuel, plus a half hour spare, so I'm all right."
Doesn't seem an unlikely scenario, and I'm sure a lot of other people would have done the same (excluding the poor fuel burn planning, diversion, and conversion error, of course
).
I still think that if the gauges showed 1/2 and 1/4 when the engines quit, as the pilot claims, then this is a serious fault, and merits more comment than has been given in the AIB report.
It doesn't mean that his planning was not at fault. However, without the conversion error, he would have made it back without an accident. Maybe the next pilot who didn't 'fill to the brim' would have had the accident? There had been 14 flights before where the aircraft had not been fuelled to the top. Perhaps they too made mistakes, but no-one is noticing, because they did not fall in someone's garden. Why has none of these previous pilots reported the severe discrepancy in the gauges - they must have noticed surely, since none of them were negligent?
I think the guy's fuel planing was poor, and it was the last link in the chain of events leading to an accident, but I still wouldn't say he was negligent.