Density altitude is pressure altitude corrected for non-standard temperature. If the temperature is hotter than standard, the air will be less dense and the aircraft will perform as if it were at a higher altitude. For example, Big Bear Airport (L35) in southern California is at 6752 ft MSL, but on an 85 degree day it has a density altitude of 10,000 ft. A 180 hp engine will produce 35% less power (117 hp) at this density altitude. Factoring density altitude into aircraft performance calculations is critical during takeoff and climb out at high altitude airports. In some cases, the runway itself may lie above the aircraft’s service ceiling, making a takeoff impossible. Even worse, the aircraft may lift off and remain aloft for a short time in ground effect, only to collide with terrain because of the inability to climb. An airplane loses 3.5% of power for each 1000 foot increase in density altitude. A good rule of thumb to maintain a margin of safety is to mentally downgrade your aircraft to a lower performance model. Thus, a Diamond DA-40 aircraft capable of carrying 4 passengers becomes a DA-20, capable of carrying only two passengers and very limited baggage. A Cessna 172 becomes a 152, etc. Another way to avoid density altitude related performance problems is to avoid flying in the mountains between the hours of 10 a.m. and 5 p.m. If there is ever any question about aircraft capability, refined calculations should be made using a flight computer and the POH.