Did it in the box as part of L1011 conversion. TOC, flew into volcanic ash at night, one by one the engines failed. Turned back, set speed then checklists for single engine failures, then multiple engine failures, hydraulic systems, electical systems pressurisation failures. Calculation of no flap, no slat speeds, checklists for that. Manual gear extension, all the time trying to relight an engine. Of course that didn't happen. Both pilots and FE working like one armed paper hangers but we did it. I think I lost weight, the session lasted about 40 minutes and I have never felt such satisfaction or confidence as then.