Well that didn't end well...

[JAZZCNC]

If at all possible avoid Plunging into material. Or like mentioned helical into it. Or at very least peck into it using peck drill cycle.

However the most likely reason your tool broke was too low feedrate and too low Spindle RPM for aluminium. 1000rpm isn't anywhere near fast enough unless was using really large cutter.
Can't really give you any figures to use because we don't have enough info regards cutter used but I'm pretty sure you'll need nearly all your 5000rpm if trying to cut aluminium.