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If the station altitude is unknown, read calibrated
altitude MSL on the middle scale and true altitude
MSL on the outer scale.
In Figure 15 the pressure altitude is 10,000 feet,
station altitude is 5,000 feet, outside air temperature is
-19°C, and your indicated (calibrated) altitude is 12,000
feet. The difference between 5,000 feet station altitude
and 12,000 feet indicated altitude is 7,000 feet. Oppo-
site 7,000 feet on the middle scale read correction to
station altitude (6,600 feet) on the outer scale—5,000
feet plus 6,600 feet equals 11,600 feet true altitude.
CAUTION: If the temperature between the sur-
face and the aircraft does not decrease at the
standard rate of 2°C per 1,000 feet or if the pressure
at flight level is nonstandard, reliance on a com-
puter solution to determine obstruction clearance
can be very hazardous.
Find True Altitude:
(Answers are on Page 38)
INDICATED/
PRESSURE CALIBRATED STATION TRUE
ALTITUDE ALTITUDE TEMP ALTITUDE ALTITUDE
1. 10,500 10,000 -20°C 5,000
2. 12,000 11,000 -30°C 3,000
3. 8,000 7,600 -15°C (unknown)
Feet Per Mile vs. Feet Per Minute
Because aircraft performance characteristics vary
dramatically between types, the FAA establishes
climb and descent requirements in feet per mile,
rather than in feet per minute. A climb of 300 feet
per mile will result in a 3° climb angle for any aircraft;
a light trainer climbing at that angle at 90 knots