According to today's newspaper, 80g of PETN would "level a house". Based on that, I think it's safe to assume that less than 10g would be sufficient to bring down an airplane.

So given that we know that terrorists have access to a stable, easily transported powdered material that it takes only 10g to bring down a plane, why is it again that we have rules in place that are designed to thwart bombing attempts using volatile liquid explosives that would have to be carefully and precisely mixed in a controlled process and would have to be in quantities over 100ml to be effective?