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Density Altitude

Effects on the Airplane
There are numerous ways that density altitude affects the airplane. For example, a normally aspirated engine will lose 3% of its power per thousand feet of density altitude increase. Next, as density altitude increases, the wings have less dense air with which to create lift. Since a propeller is an airfoil, it too will be less efficient.

Effects on Performance
All of these factors affect the overall performance of the airplane. At higher density altitudes, takeoff and landing distances are increased, rate of climb and actual service ceiling are decreased, true airspeed is higher for a given indicated airspeed, and turning radius is larger at high altitude at a given indicated airspeed.

To help regain some of the lost takeoff and landing performance at high density altitudes, you should reduce the weight at which you fly the airplane to no more than 90% of maximum gross weight. For a typical light airplane with a maximum gross weight of 3,000 pounds, reducing the loaded weight to no more than 2,700 pounds will regain much of the lost performance. A check of your airplane's performance data should show that takeoff and landing distances, climb rates, and single engine performance for multi-engine aircraft is greatly improved at this reduced weight. Turbocharged aircraft will gain some improvement, but it will be somewhat less than that gained by non-turbocharged aircraft.

Since your true airspeed is higher for a given indicated airspeed, many pilots will respond to the visual cues of higher ground speed on takeoff by rotating at a lower IAS than normal. Instead, you should use the same IAS for takeoffs and landings as you would at seal level (or that the Pilots Operating Handbook specifies). Rotating at too slow an airspeed may cause the airplane to take an even longer ground run than necessary.

Turning radius is proportional to the square of true airspeed. For example, if you increase your TAS by only 10%, your turn radius will increase by 20%. In the pattern this may result in a wider than expected turn to final resulting in overshooting. At high density altitudes, many pilots will fly slightly wider patterns to account for the wider turns.

Higher density altitudes also affect best rate and angle of climb airspeeds. Best rate of climb IAS decreases as altitude increases, while best angle IAS increases slightly. Refer to your airplanes¼s handbook to be sure you are flying the correct airspeeds to get the performance you expect.

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