Aussie27, what you said re the TPE's is not exactly true; I was a junior F/O flying Metro 2's a few years back. One fine day as we were entering the circuit at the usual speed (Vmo minus about 5...) I was stunned when the skipper whipped the power levers past the idle stops. It was completely unintentional on his part - the whole throttle setup had become so worn over the many years in service that there was almost no pressure required to lift them over the gate.
Thankfully he reacted almost instantly and pushed them forward again, but in those couple of seconds the aircraft yawed all over the sky. Quite memorable.
I guess in hindsight that had he pulled them back gently, instead of smacking them back, it may well not have happened. But we tried it on the ground in much newer 23's and you couldn't do it even if you abused them (engineers were present).
It was the first thing I thought of when I read about the PNG crash. Those in the know might like to tell us whether power lever hardware wearing with time could cause unintentional movement aft of flight idle.