Double heading is an interesting proposition. On steep grades where both locomotives need to work to get up the grade, it is a function of the crews trying to take equal loads. There are countless stories out there about crews that did not get along and one or the other would loaf. I have never had the privilege of double heading on steep mountain grades, however I did quite a few double-headed mainline trips to Harrisburg, Enola, Rockville, and Philadelphia. Along those routes there were grades that probably exceeded the capacity of either of the Pennsy locomotives we operated, most notably the climb out of 30th Street station, which I am told used to stall GG-1 locomotives. On the grades, the process was pretty simple. Otherwise, both engineers needed to be very much in tune with what the other was doing so as not to bang the train around from unwanted slack action.
I always ran the lead engine, Atlantic #7002 and I would communicate with the second engineer with the whistle and hand signals we had worked out between us. The lead engineer has the job of assessing the situation ahead and anticipating what to do based upon knowledge of physical characteristics, visual, and above all - what the pilot said, since this was mostly new territory to us. The second engineer has an arguably more difficult job in that he/she needs to react to what the lead engine is doing in such a way as to not bang around the train. Our second engineer for all those trips was Jim Rice on American #1223, and he was truly excellent at providing the amount of help when needed and "floating" the second engine when not needed. I found the Harrisburg line, westbound from Elizabethtown to Lancaster to be the most difficult to run and not exceed 60 mph, our usual speed limit. The line is a series of gentle ups and downs, with the downs being just enough to increase your speed significantly with only enough throttle to keep the slack stretched.
I found the EBT Spectacular double, triple, and quadruple headers to be a royal pain in the rumpus. Without enough load for one locomotive and going up and down to boot, trying to control slack and speed was a somewhat haphazard process. It also annoyed me because the original EBT set up their operation specifically to avoid double heading. Smart move.
