I always thought it interesting a committee headed by three men did the recommendation on going to two-man cockpits. One from industry, one FAA, one union.
To John T's point, I quite agree you can find examples of successful and unsuccessful crews, the number of crewmembers in the cockpit being irrelavant. The two-man crew on AF90 did not deal well with their icing problem at DCA, the three man crew in the recent C-5 accident performed horribly; but the three-man crew with Al Haynes or the other UAL 747 incident were absolute paragons of CRM and efficiency. I liked working with engineers, but insisted that they act as part of the crew and could speak up at anytime-emphasized that they would be killed by my mistake as I could be by their's.
My only reservation with two-man crews in an emergency is that one becomes very concentrated with flying, one with the emergency drills and NO one cross-checking the other, unless they are very competent and using the automation correctly and fully. Despite the claims of engineers, two-man planes can be a handful in emergency. In a two-man cockpit, I feel better if automation is being utilized, it is hard to be heads-down working an emergency checklist while I know the other is hand-flying a SID or an approach.
GF