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Standard Day?


r22butters
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Its been a while since I studied this, so bear with me. :D

 

I remember being told that, at sea level, with a DA of 6000', its the same as being at an airport who's field elevation is 6000' on a Standard Day.

 

1. Does that mean that at that 6000' airport the temperature is 15C, and the pressure is 29.92 in. Hg?

 

2. At that 6000' airport, if I set the altimeter to 29.92, it will read 6000'PA/DA as well?

 

3. Is a Standard Day and a Standard Atmosphere the same thing?

 

4. The book said that a Standard Atmosphere is 15C and 29.92 in. Hg, at sea level. So, above sea level do those values change, or is a Standard Atmosphere always 15C and 29.92 in. Hg.?

 

5. Density Altitude is Pressure Altitude corrected for non-standard temperature. So, is non-standard temperature anything above or below 15C?

 

6. When the temperature is 15C is the pressure always 29.92 in. Hg.?

 

:huh:

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1. Standard temperature lapse rate is 2C/1000 ft. So at an airport at 6000', a standard day would be at 3C.

 

2. When you set you altimeter to 29.92, you are reading your pressure altitude. I think theoretically, you should read 6000' if the temp is at 3C, but its unlikely to happen because of different weather patterns and pressure changes.

 

3. Yes

 

4. The temp changes at a standard lapse rate of 2C/1000'.

 

5. Non standard temperature is anything above or below the standard temperature for a particular altitude (15C - 2C/1000')

 

6. No, weather fronts change the pressure, so even at standard temp for an altitude, your not always going to be at 29.92. I'm not 100% about it though, honestly ive never really paid much attention to it while flying aside from calculating DA on the charts.

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Good answers from RW already, but a few other things.

 

  1. The atmospheric pressure will also lapse at 1" per 1000' BUT this shouldn't be confused with the altimeter setting. On a standard day at a 6000' MSL airport, the temp will be 3C, the altimeter setting will be 29.92, and the pressure read off a barometer would be 23.92.
  2. If, on a standard day, you were at that 6000' MSL airport and you set your altimeter to 29.92, it would read 6000'. Pressure and density altitude would be the same under those conditions. If it were hotter or colder than standard, or the altimeter setting was something other than 29.92, then the altimeter would not read 6000.
  3. sure
  4. A standard day is any day that the temp is 15C corrected for altitude and the altimeter setting is 29.92.
  5. As RW said.
  6. Nope. Temp and pressure can be independent.

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