Figure 1-3 Path of Aircraft Flying A Constant Indicated Altitude with Decreasing Temperature

AVIATION WEATHER

CHAPTER ONE

Temperature

Aircraft altimeters are calibrated for a standard lapse rate. An incorrect altitude indication will

result if the temperature deviates from the standard. For every 11C that the temperature varies

from the standard, the altimeter will be in error by 4%. If the air is colder than the standard

atmosphere, the aircraft will be lower than the altimeter indicates. If the air is warmer than

standard, the aircraft will be higher than the altimeter indicates (Figures 1-3, 1-4, and 1-5). You

may notice the rules presented in the pressure section, above, also apply to temperature

deviations.

700mb

800mb

Warm Air

900mb

Cold Air

900mb

Pensacola

Jacksonville

Sea level pressure at both towns is 1013.2mb

Figure 1-3 Path of Aircraft Flying A Constant Indicated Altitude with Decreasing

Temperature

TEMPERATURE

ALTIMETER

ACTUAL MSL ALTITUDE

CHANGE

Flying from standard temp.

Indicates higher than actual

Lower then indicated

toward lower temp.

Flying from standard temp.

Indicates lower than actual

Higher than indicated

toward higher temp.

Figure 1-4 Temperature Deviation vs Indicated and MSL Altitude

Figures 1-3 and 1-5 show that as you fly from warm to cold air, an altimeter will read too high

and the aircraft is lower than the altimeter indicates. Over flat terrain, this lower true reading is

no great problem; other aircraft in the vicinity are also flying indicated altitudes resulting from the

same temperature and pressure conditions, and the altimeter readings are compatible because the

errors result from the same conditions.

General Structure of the Atmosphere, and Atmospheric Temperature and Pressure 1-5