Oldie but a goodie here. With summer weather (and the TFP Mountain Flying Trip) coming up, it's time to refresh yourself on high density altitude flying.
While we're on the topic, "high density altitude" can be a confusing phrase. I once spoke to a pilot who had been confused about density altitude for years, because he or she thought we were talking about flying at altitudes with high density. To the contrary, we are talking about flying in conditions where the density altitude is high (and air density is therefore low).