RAT 5
The very point I am trying to make is that line pilot has a brief on how to go about doing his business that doesn't include any testing with passengers on board. Air Asia Indonesia trying to find if it is possible to reset CBs in flight, Pinnacle flight 3701(though no pax) trying to find out how high can you reach are the examples that makes for tragic reading. There is a long list of what is possible. To have real practice of OEI in flight, direct law in flight is possible but you simply don't do it. Besides what's the purpose? you want to develop manual flying skills do it the recommended way, just switch off automatics and do it. The medicine should not be deadlier than the disease.