This FCCA train has just left the switchbacks of Casapalca and is now headed for Chinchan.
In addition to the pain in the head (due to the altitude if you didn't have time to acclimatize), photographing the FCCA can be a big pain in the butt: First there's the weather, which usually is bad (cloudy to foggy to overcast), at least for the second half of the day. Then there's the very erratic traffic. You can easily encounter a train in the morning somewhere along the line, then go a few km ahead and wait for it, without ever seeing it again for the entire day. Shunting operations at stations can easily take several (!) hours, or the engine may suddenly break down anywhere along the line. Even reversing at a simple switchback can end up in an epic shunting operation, because the tracks are often too short and some sidings in the vicinity have to be used to temporarily store some cars.
If you combine that with some camera issues, you may end up with a pretty furious railfan. Luckily the train was followed by this one a bit later and the railfan was happy again.