The Effects of Density Altitude on Aircraft Performance

    Pilots have more than just the four fundamental forces to worry about to fly safely. Density altitude is arguably one of the biggest environmental factors to account for. Density altitude is defined as, “the pressure altitude corrected for nonstandard temperature variations” (Federal Aviation Administration, 2008). The standard temperature is 59 °F at sea level or 29.92 "Hg. The standard temperature goes up with the rise in elevation.  

    If there is a different temperature than the standard temperature, then the nonstandard temperature should be taken into consideration by the pilot for the expected aircraft performance. During takeoff and landing, this becomes crucial. The owner of Leadville-Lake County Airport describes the effects of density altitude, “as the density altitude goes up, the plane thinks it’s at a higher altitude” (Romano, M. 2001, Feb 04). An aircraft at higher altitudes will react differently to flight control inputs than an aircraft at lower altitudes due to the air being less dense. Density altitude can decrease flight performance with higher altitude and temperature (Federal Aviation Administration, 2008). The air becomes less dense as the altitude increases. When the air is less dense, power, thrust, and lift are reduced leading to decreased aircraft performance (Aviation Supplies & Academics, 2016).  

 FAA–P–8740–2  Chart

    Pilots can combat the decreased plane performance due to higher density altitude by increasing the takeoff distance. The power is reduced at higher density altitudes because the engine takes in less air. The air molecules are more compact at lower altitudes allowing for more thrust to be generated by the propellers and at the same time, more power to be produced by the engine (Aviation Supplies & Academics, 2016). While temperature is an independent environmental variable, pilots can schedule their flights at cooler times of the day if applicable. For example, the hours between 12 pm and 4 pm are likely to be hotter than 5 am or 9 pm. The option to change flight times for an airline pilot may not be likely, but maybe a private pilot could choose this method to increase flight performance and efficiency. Another option to help offset the decreased performance may be to decrease the gross weight. If the aircraft is acting like it is at a higher altitude than it actually is due to the high density altitude, then the added weight would affect the ability of the aircraft to lift. Therefore, the rate of climb would also be affected. Pilots have a lot to account for before ever taking off. That's why preflight preparations for things like density altitudes are so important for safe flights.

References

Aviation Supplies & Academics. (2016). Ch. 11 Aircraft Performance. In Pilot's Handbook of Aeronautical Knowledge: Faa-H-8083-25B. https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/phak/13_phak_ch11.pdf. 

 

Federal Aviation Administration. (2008). Density altitude FAA–P–8740–2 AFS–8 https://www.faasafety.gov/files/gslac/library/documents/2011/Aug/56396/FAA%20P-8740-02%20DensityAltitude[hi-res]%20branded.pdf 

 

Romano, M. (2001, Feb 04). FLYING IN THIN AIR CHALLENGE FOR AIRCRAFT AS TEMPERATURE RISES, HIGH `DENSITY ALTITUDE' PHENOMENON ROBS PLANE OF POWER, PERFORMANCE: [FINAL EDITION]. Rocky Mountain News http://ezproxy.libproxy.db.erau.edu/login?url=https://www-proquest-com.ezproxy.libproxy.db.erau.edu/newspapers/flying-thin-air-challenge-aircraft-as-temperature/docview/413358681/se-2