1. Aviation Weather Hazards: Density Altitude
“Don’t let the DA get you.”

2. Density Altitude
Several FAA Handbooks define DA as “pressure altitude corrected for non-standard temperature.”
S271, Chapter 5 defines DA as “pressure altitude corrected for temperature and humidity.”
Problem: FAA handbooks, pilot training and testing materials, and manufacturer flight manuals DO NOT provide a chart, equation, or method by which to calculate the effects of RH.
In S271, we generally teach that, since the effects are minimal, and we don’t have the charts or tools to factor in RH, we can just ignore it.

3. Density Altitude is sometimes taught as “the altitude the aircraft thinks it is at, and therefore performs accordingly.”
To determine DA, we need to know only three items of information:
Elevation of the airport, helibase, or helispot.
Current Barometric Pressure
(in order to calculate Pressure Altitude)
Temperature
If you know your location elevation, the Barometric Pressure and Temperature information can be acquired with ONE phone call.

4. Who are you going to call?

5. What is “Pressure Altitude?”
Pressure altitude is the altitude displayed on an altimeter when it is set to Standard Pressure as adopted by the International Civil Aviation Organization (ICAO) in is the STANDARD pressure in the world of International Standard Atmosphere (ISA).

6. better for aircraft performance than LOW pressure.
When barometric pressure is above or below the “standard” inches of Hg, Pressure Altitude (PA) will be lower or higher than field elevation. This table may be used to calculate Pressure Altitude.
ADD
feet
SUBTRACT
feet
Note: HIGH atmospheric pressure is
better for aircraft performance than
LOW pressure.

7. What is “Standard” vs. “Non-Standard” TEMPERATURE?
The International Civil Aviation Organization (ICAO) baseline for all aircraft performance data is a “Standard Temperature” of 15 deg. Celcius (or 59 deg. F) AT SEA LEVEL, with zero RH.
The global mean standard atmospheric lapse rate is 2 deg. C (or 3.5 deg. F) per 1,000 ft. of altitude (up to 36,000 ft.)

8. Standard Temperature at MSL Altitudes
Altitude Deg. (C) Deg. (F)
14,
13,
12,
11,
10, 9, 8, 7, 6, 5, 4, 3, 2, 1,
Sea level
To determine DENSITY ALTITUDE, add ft. to the Pressure Altitude for each degree Celcius above standard temp.

9. Solve for. Airport elevation: 7,420 ft. Density Altitude
Solve for Airport elevation: ,420 ft. Density Altitude Altimeter/Barometer: ” Temp deg. F or 27 C (Std. temp. at 7,500 = 0 deg. C)
feet
Airport Elevation (MSL) ,420
Correct for non-std. pressure
Pressure Altitude (PA) = ,000’
Current temp. is 27 deg.
warmer than std. temp.
Calculate for non-std. Temp.
27 X ft. = 3,170 ft. PA 8,000’
Add temp. factor to PA: ,170
DENSITY ALTITUDE = 11,170’

10. The non-standard temperature conversion is usually calculated via the Density Altitude chart shown below.
A copy of this chart can be found in Chapter 10 of the FAA “Pilot’s Handbook of Aeronautical Knowledge” available at and in several Aviation and Weather publications.

11. What about Humidity?
Is the effect significant?

12. ASOS and AWOS Recordings are updated every minute.
Temperature and Dew Point are factored into the Density Altitude given at the end of the report.
High RH can contribute over 500 ft. to Density Altitude.