One of the couplers has been moved. The saw head pulled off the shaft, the shaft pulled out of the engine, When you put the saw in the air the drive shaft slips out of the coupler preventing it from turning the saw.
Are you referring to the "engine" quit running? Or like you said "the saw (only) quits running. The previous poster ILENGINE assumes, like I do too, that it is not the engine that quit, but the mechanics of the saw itself that fails.
More info: model #446 gas, pole saw. The engine stops running (like it was out of gas) in vertical position only. Can prevent it from stop running by getting it horizonal quickly. The chain is engaged in both position.
Hope this helps and thanks for pointing out the void of information.
I would second the fuel line problem.. fuel line were is connects to filter may have split and filter came off and the end of the line is not heavy enough to stay at bottom of tank.