If the sky was clear, as the article states, then lack of GPS is not a good enough excuse for a trained pilot to crash into a mountain, unless the cockpit has no windows.

It's not fun to lose GPS, but, a trained pilot ought to have been able to handle this situation fine. All instruments can fail, but weather notwithstanding, no instruments are required to land a plane back down on a runway (implied in my statement is that, if you lose all your instruments, you should still try to land rather than continue your flight).

At the end of the day, if you aren't proficient in VFR, then your IFR proficiency doesn't mean much. Hopefully this pushes the relevant flight schools to do more training, because this crash appears highly avoidable - and while the pilots take some amount of blame since they are behind the controls, there are also people who failed them by not giving them sufficient training.