Higher density altitude means lower aircraft performance. When outside is high, hot, and (to a much lesser extent) humid -- density altitude will be higher and aircraft performance is worse. Remember: [[Hot, High, and Heavy]] ***Definition*** :: Pressure altitude corrected for nonstandard temperature. Density altitude is used in computing the performance of an aircraft and its engines. ***In Other Words:*** The altitude the aircraft 'thinks' it's flying at. ***Source*** :: [[PHAK Glossary]] #glossary