Density altitude?

Question

You are computing take-off performance from Calgary, Intl. Aiport where the field elevation is 4,000' MSL and the altimeter setting is 29.92" Hg.; the outside air temperature is -22 F. What is the density altitude?

Answer 1

fighterace26 was right,

4000 is PRESSURE altitude at 29.92. -22 F (30c)

= -796

Answer 2

The altimeter setting being 29.92 makes this one easy. This is also the setting you would use in the aircraft to determine "pressure altitude." With other altimeter settings, you need to convert the airport elevation to Pressure altitude. use the Density Altitude Charts' PA conversation factor, subtract/add height using the current altimeter setting, this gives you Pressure altitude, locate this altitude on the chart where it intersects the temp. draw a line 90 degrees to the left, read DA.

To find this chart go to http://www.faa.gov/education_research/testing/airmen/test_questions/media/FAA-CT-8080-2E.pdf
Figure 8

Answer 3

If you have your electronic E6B, it should be VERY easy to compute this. And, if you have the (old) slide-rule E6B, it's a bit more involved but still rather straightfoward. Unless my E6B is messed up or I put in erroneous information (ind. alt is 4000, temp is -30C, baro is 29.92), then the DA is 816 below sea level. Note: Be sure to convert the -22F to centigrade!

Answer 4

I went to grab a flight manual to answer this question, and someone had gone and cleaned me out! I actually had to leave my office, go upstairs, find my manuals, and confirm that yes, 796 below sea level would be correct.

Alas, the pains I have to go through at work!

Answer 5

796 ft BELOW sea level,

If you are a student pilot you really should buy an E6B calculator