"It's actually used as a 'primary' explosive; ie one that detonates another, more powerful charge such as C4."
I believe, Guv, that the "more powerful charge" was the fuel tanks. That may explain why he did not go to a lavatory and ignite the charge in privacy. They are full aft and full forward. His seat was over the tanks.
In which case this was a pretty dam' sophisticated plan.....