The problems associated with density altitudes are usually only considered when flying
from high elevation airfields and bearing in mind the fact that the highest terrain quoted
on the Jacksonville Sectional Chart is 720 feet above sea level and only 305 feet above
sea level on the Miami sectional, you may have thought they could be discounted.
You would be wrong. With the high temperatures and high humidity experienced in
Florida the problems associated with density altitude can be in existence even when the
airfield you are operating from is virtually at sea level.
Density altitude is a measure of air density. As air density decreases, density
altitude increases. The further effects of high temperature and high humidity are
cumulative, resulting in an increasing high density altitude condition. High density
altitude reduces all aircraft performance parameters, which means the normal engine
horsepower is reduced, propeller efficiency decreases and a higher true airspeed is
required to sustain the aircraft throughout its operating range.
This does, of course, also mean an increase in runway length requirements for both
takeoff and landing, and a decreased rate of climb. As an example, a light aircraft
requiring 1,000 feet of runway for takeoff at sea level under standard atmospheric
conditions will require double that length at an equivalent density altitude of 5,000
feet.
Great care should therefore be exercised when operating under significant density
altitude conditions and the advice of a Flight Service Station should be sought. The full
range of services provided by Flight Service Stations are covered in a later section.
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