1fa. Using Altimeters to Monitor AltitudeTo maintain the correct
altitude throughout a flight most airplanes use a pressure
altimeter—essentially an aneroid barometer with a scale reading in feet
instead of inches of mercury, mb, or hPa. An altimeter does not directly
measure “true” altitude above the ground or mean sea level. Instead,
the altimeter reflects pressure altitude, which is the height of a given
pressure surface.When the pilot says ”we have attained our cruising
altitude of 33,000 feet,” what he or she means is that ”we have arrived
at our assigned pressure surface.” (Assigning flights to a given
pressure surface helps to maintain safe vertical separation between
aircraft on the same route).Altimeter settings must be calibrated with
sea level pressure. Without recalibration, a plane flying across isobars
from high pressure to low pressure will be at a lower altitude than the
altimeter indicates (Figure 4-6-1). To ensure that the plane will fly
at a safe height above a mountain range, for example, the altimeter’s
settings must be updated frequently using air-pressure data from nearby
airports or weather stations. Recalibrating the altimeter to air
pressure at the destination airport assures that the aircraft will land
at the proper elevation.Temperature changes beneath the plane also
affect altimeter readings (Figure 4-6-2). Where temperature is lower,
the altimeter indicates you are higher than your true altitude.FIGURE
4-6-1 Effect of pressure on reliability of altimeter readings for an
uncorrected altimeter....FIGURE 4-6-2 Relationship between temperature,
indicated altitude, and true altitude....What factors must a pilot take
into account in using an altimeter to keep an aircraft at a constant,
true altitude? Explain. Get solution
