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During a flight in colder-than-ISA air the indicated altitude is...

  • A

    Higher than the true altitude.

  • B

    Lower than the true altitude.

  • C

    Equal to the true altitude.

  • D

    Equal to the standard altitude.

Temperature has an effect on the accuracy of barometric altimeters, indicated altitude, and True Altitude. The standard temperature at sea level is 15º Celsius (59º Fahrenheit). The temperature gradient from sea level is minus 2º Celsius (3.6º Fahrenheit) per 1 000 feet. For example, at 5 000 feet above sea level, the ambient temperature on a standard day would be 5º Celsius.

When the ambient (at altitude) temperature is colder than standard, the aircraft's true altitude is lower than the indicated barometric altitude. When the ambient temperature is warmer than the standard day, the aircraft's true altitude is higher than the indicated barometric altitude.

When flying into a cooler air mass while maintaining a constant indicated altitude, true altitude is lower. “FROM HOT TO COLD, LOOK OUT BELOW”.

When the air is warmer than standard, the aircraft is higher than the altimeter indicates.

During a flight in colder-than-ISA air the indicated altitude is higher than the true altitude.

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