Aviation Weather Hazards:
Density Altitude
“Don’t let the DA get you.”
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.
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.
Who are you going to call?
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 1964.
29.92 is the STANDARD
pressure in the world of
International Standard
Atmosphere (ISA).
When barometric pressure is above or below the “standard” 29.92
inches of Hg, Pressure Altitude (PA) will be lower or higher than field
elevation. This table may be used to calculate Pressure Altitude.
ADD
28.3
28.4
28.5
28.6
28.7
28.8
28.9
29.0
29.1
29.2
29.3
29.4
29.5
29.6
29.7
29.8
29.9
1535 feet
1435
1340
1245
1150
1050
955
865
770
675
580
485
390
300
205
110
20
SUBTRACT
29.92
30.0
30.1
30.2
30.3
30.4
30.5
30.6
30.7
30.8
30.9
31.0
0 feet
- 75
- 165
- 255
- 350
- 440
- 530
- 620
- 710
- 805
- 895
- 965
Note: HIGH atmospheric pressure is
better for aircraft performance than
LOW pressure.
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.)
Standard Temperature
at MSL Altitudes
Altitude
14,000
13,000
12,000
11,000
10,000
9,000
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
Sea level
Deg. (C)
-13
-11
-9
-7
-5
-3
-1
1
3
5
7
9
11
13
15
Deg. (F)
10
13.5
17
20.5
24
27.5
31
34.5
38
41.5
45
48.5
52
55.5
59
To determine
DENSITY
ALTITUDE, add
117.4 ft. to the
Pressure Altitude
for each degree
Celcius above
standard temp.
Solve for
Density Altitude
28.5
28.6
28.7
28.8
28.9
29.0
29.1
29.2
29.3
29.4
29.5
29.6
29.7
29.8
29.9
29.92
30.0
30.1
30.2
30.3
30.4
1340
1245
1150
1050
955
865
770
675
580
485
390
300
205
110
20
0 feet
-75
-165
- 255
- 350
- 440
Airport elevation:
7,420 ft.
Altimeter/Barometer: 29.3”
Temp.
80 deg. F or 27 C
(Std. temp. at 7,500 = 0 deg. C)
Airport Elevation (MSL)
Correct for non-std. pressure
7,420
+ 580
8,000’
Pressure Altitude (PA) =
Current temp. is 27 deg.
warmer than std. temp.
Calculate for non-std. Temp.
27 X 117.4 ft. = 3,170 ft.
Add temp. factor to PA:
DENSITY ALTITUDE =
PA
8,000’
+ 3,170
11,170’
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 www.faa.gov
and in several Aviation and
Weather publications.
What about Humidity?
Is the effect significant?
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.