When it comes to aircraft performance and pilot procedure, a problem area that continues to plaque us is takeoffs and landings associated with density altitude. Aircraft performance can vary greatly based on temperature, air pressure and airfield elevation. We relate temperature to air pressure to obtain density altitude, which is defined as pressure altitude corrected for variations from standard temperature. When conditions are standard, the pressure altitude is the same as density altitude.
Aircraft performance charts are based on the "standard atmospheric day".It is important for pilots to understand that a standard day is not typical. Temperature changes affect density altitude. At sea level, the "standard atmospheric day" temperature is 59 deg F and decreases at a rate of 3.6 deg F per 1000 feet for the altitudes typical GA aircraft operate at. As an example, the temperature for a "standard" day in X City is 39.9 def F. Certainly a 40 deg F day during the summer in X City would not be considered typical. Any higher temperature, without an offsetting increase in atmospheric pressure, will increase the density altitude. An aircraft subjected to high density altitude will not give the performance anticipated by a pilot casually reviewing the performance charts.
Even though the surrounding terrain may look wide open and relatively flat, on a typical summer day some light airplanes could be at or close to their service ceiling before even leaving the ground. Check the density altitude and the appropriate performance charts in the airplane flight manual or the pilot operating handbook (POH). Remember no summer day is standard.
The density altitude can also influence landing distances. Just as with takeoff and climb performance, your landing distance will e much longer in conditions with a high density altitude. Again, it is important to calculate landing distances from the appropriate performance charts and use the correct density altitude.
-Small Airplane Directorate, FAA
Aircraft performance charts are based on the "standard atmospheric day".It is important for pilots to understand that a standard day is not typical. Temperature changes affect density altitude. At sea level, the "standard atmospheric day" temperature is 59 deg F and decreases at a rate of 3.6 deg F per 1000 feet for the altitudes typical GA aircraft operate at. As an example, the temperature for a "standard" day in X City is 39.9 def F. Certainly a 40 deg F day during the summer in X City would not be considered typical. Any higher temperature, without an offsetting increase in atmospheric pressure, will increase the density altitude. An aircraft subjected to high density altitude will not give the performance anticipated by a pilot casually reviewing the performance charts.
Even though the surrounding terrain may look wide open and relatively flat, on a typical summer day some light airplanes could be at or close to their service ceiling before even leaving the ground. Check the density altitude and the appropriate performance charts in the airplane flight manual or the pilot operating handbook (POH). Remember no summer day is standard.
The density altitude can also influence landing distances. Just as with takeoff and climb performance, your landing distance will e much longer in conditions with a high density altitude. Again, it is important to calculate landing distances from the appropriate performance charts and use the correct density altitude.
-Small Airplane Directorate, FAA
