Can you flag down / contact an airplane with a handheld radio in case of emergency? A friend and I are going rim to rim to rim in the Grand Canyon this Wednesday.  It's a 46mi, 20+hr "hike" with some very physically challenging sections.  We are packing the minimal amount needed - meaning not too much extra in case of an emergency - it's especially risky given the below zero (fahrenheit) temperatures this time of year.  Normally for something like this, I would bring my Spot - to call for help if I needed to, but it's not working.

If I brought my VXA-220, would it be legal to use it to call for help?  From what I understand, most airliners are tuned into 121.5.  Could I tell them to send a helicopter for rescue?

Obviously, in a life or death situation it's not going to matter if I'm braking the law.  But it would be nice to know how such a situation would be handled.
Yes, this is legal. As far as I understand, it used to be common practice, and some hiker's beacons still squawk 121.5. Nowadays, more advanced beacons are suggested, but it sounds like yours isn't working. Some police and EMT stations still monitor 121.5, too.