MART Vol. II MO/MP - NESA - Civil Air Patrol

Assume an aircraft is taking off from an airport with a pressure altitude of3,000' and the temperature is 80º F. Draw a line straight up from 80º F to theintersection of the 3,000' pressure altitude line. Then proceed horizontally to theleft to read the density altitude (5,000').Flight Computer methodConvert the 80º F to Celsius (27º). Position +27 on the "Air Temperature ºC"scale over the pressure altitude of '3' (the pressure altitude scale is in thousandsof feet). Read the number ('5') in the "Density Altitude" window (5 x 1,000' =5,000').[Note: A rule of thumb is to add 500 feet to the airport’s elevation for every 10ºF above standard temperature at the airport’s elevation.]4.2 Aircraft performance limitationsThe combined effects of high altitude and temperature (high density altitude)can have a significant effect on performance of aircraft engines, wings, propellers,and the pilot and crew. If all missions were conducted on cool, low humidity daysalong the Gulf coast there would be no concern with air density and itsimplications on flight safety. Obviously, this isn't the case. In fact, theseconditions have often been primary factors in aircraft accidents, and may result inloss of the search aircraft, unless you pay careful attention.The most noticeable effect of a decrease in pressure (increase in densityaltitude) due to an altitude increase becomes evident during takeoff, climb, andlanding. The purpose of the takeoff run is to gain enough speed to generate liftfrom the passage of air over the wings. If the air is thin, more speed is required toobtain enough lift for takeoff: hence longer ground runs. An airplane that requiresa 1,000' run for takeoff at a sea-level airport will require a run almost twice as longat an airport that is approximately 7,000' above sea level.61