Had a -28 go out on a king air once. Starting the decent out of fl220, as I reduced the power the left engine started compressor stalling. I put the power back up and everything ran fine until I brought back the power back before the final app fix where it really made some loud bangs. Again I increased the power and it went away until short final where all hell broke loose. The engine started surging, the torque and fuel flow fluctuated with every bang. At this point we were already commited to landing so we touched down and went into a little reverse as we slowed down. The thing didn't stop coughing until we came out of high idle. When taxing to park each time the engine accelerated out of idle the engine gave off a Garrett howl like on the MU-2.

Turns out what happened was the oil pump started to fail and the insides started eating into the housing. It caused enough drag in the 85-71% n1 range to cause a compressor stall. It never even have off a chip detect or decrease in oil pressure. Needless to say, I'm glad it happened that way, I couldn't imagine what a complete oil starved pt-6 sounds like as it welds itself together.

The engine was 3600 since new I believe.