So what's the big deal when the aircraft is on the ground with its engines switched off? An SIA pilot told me that it was only forbidden while the aircraft has its engines running - that would make sense. However, it seems members of the cabin crew have their own interpretation of the rules, the men amongst them being simply being the offensive morons that they are. American airlines won't allow it at all but then they are paranoid having made it so easy for the terrorists in the first place, so much for America always claiming to liberate us huh!
