Density Altitude Calculation

Density altitude calculations

Calculate the density altitude at 3600ft ASL with OAT of 28°C & -20°C with altimeter setting of 29.82 (OAT = outside air temperature)

In this example there will be 4 calculations. 

1. calculate pressure altitude
2. calculate the standard temperature for the airport elevation (we have already done this in previous lesson)
3. calculate density altitude based on OAT of 28°
4. calculate density altitude based on OAT of -20°

1. PA

• PA = 3600 + 1000 x (29.92 – 29.82)
• PA = 3600 + 1000 x (.1)
• PA = 3600 + 100
• PA = 3700ft (the aircraft would perform as though it were flying at 3700ft)

2. Standard temp = 15° – (3600/1000 x 2°) = 7.8°C

DA = PA + (120 x (OAT – ISA standard temp))

3. Calculation 1: OAT is 28°C

• DA = 3700 + (120 x (28° – 7.8°))
• DA = 3700 + (120 x 20.2)
• DA = 3700 + 2424
• DA = 6124ft

Therefore on a hot summer day in Calgary an aircraft would perform as though it were operating at 6124ft instead of the 3600ft elevation of the airfield!

4. Calculation 2: OAT is -20°C

• DA = 3700 + (120 x (-20° – 7.8°))
• DA = 3700 + (120 x -27.8)
• DA = 3700 + -3336
• DA = 364ft

The aircraft on a cold winter day at YYC would perform as though it were operating at an altitude of only 364ft!

From the above calculations it is clearly evident that cold temperatures support the production of lift way better than hot weather does. 

The above plays a role for UAV flights too, however, at a certain temperature the tradeoff between colder air producing better lift and the same cold air negatively affecting battery life comes into effect.