ISA, Basic Altimetery Flashcards

1
Q

What 3 variables describe the state of the atmosphere under ISA?

A
  • temperature
  • pressure
  • density
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2
Q

What is the standard atmosphere conditions, and the average tropopause height?

A

Temp. 15 c or 59 F
Pressure 29.92 or 1013.25
Tropopause Standard Height = 36,000’

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3
Q

What is pressure defined as?

A

F = Mass * Gravity / Area

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4
Q

Define: Station Pressure

A

A measurement of the weight of the atmosphere above the instrument

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5
Q

What are the different types of barometers?

A
mercurial barometer (more accurate)
aneroid barometer (more portable)
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6
Q

What is virtual temperature?

A

The temperature the air would be if all the water vapor were removed and its density remained constant (always warmer than ambient)

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7
Q

What temperature should you use in density altitude calculations for more accuracy?

A

virtual temperature

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8
Q

What is the altimeter setting, and how is it found?

A

It is the station pressure (for an elevation 10 feet above the mean runway elevation) reduced to sea level, using ISA. (DC-3 altimeter is 10 feet above ground)
station pressure + [0.0011 * height above sea level]

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9
Q

When is the true and indicated altitude different?

A

Difference is greatest when temp. is below standard

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10
Q

What is QNE?

A

Standard (set at 29.92) - positive separation by pressure level

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11
Q

What is QNH?

A

Altimeter setting - should read field elevation on the ground

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12
Q

What is QFE?

A

Using station pressure - should read “0” on the ground

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13
Q

What is the lowest usable FL if altimeter seeting is less than 29.92?

A

Above FL180, FL180 if altimeter setting is above 29.92

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14
Q

For every 11Cc that the temperature varies from standard, the altimeter will be in error by how much?

A

4%

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15
Q

High density altitude affects aircraft performance in what three major ways?

A
  1. Reduced power
  2. Reduced thrust
  3. Reduced lift
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16
Q

How is stability defined?

A

The faster the atmosphere “gets cold” with increasing altitude, the more unstable it is. Low-level moisture, underlying dry air aloft, enhances instability.

17
Q

What is the lifted index?

A

The temperature of the environment at 500mb minus the temperature of the parcel of air at 500 mb

18
Q

What is precipitable water?

A

amount of water vapor from surface to 500mb and condense it in a beaker the depth of that water in the beaker. 1” of water equals 10-12” of snow