Finding TAS given IAS, altitude and OAT:-
Use calculator side of the computer.
1. Align altitude and air temp in the small window "FOR TAS AND DENSITY ALTITUDE"
2. Locate the IAS on the "B"scale (inside scale) . The "B" scale is labeled as "CAS" which for practical reasons is the same as IAS.
3. Find the TAS on the "A" scale (outside scale) immediately above the IAS.
EXAMPLE:
What is the TAS under the following conditions: altitude 10,000 ft, temp -10 C; IAS 130 Kts?
Answer: 150 Kts
Finding True Altitude given indicated altitude and pressure altitude.
EXAMPLE:
Pressure altitude is 7000 ft, Indicated altitude is 6500 ft (on the altimeter), temp is -10C, what is the true altitude?
Locate -10C and Pressure Altitude of 7000 ft on the "FOR ALTITUDE COMPUTATIONS" window. From the "B" scale and locate the Indicated Altitude of 6500 ft. Look directly over this value and find the true altitude is 6250 ft.
At a Pressure Altitude of 7000 ft, and an indicated altitude of 6500 ft the TRUE ALTITUDE is actually 6250 ft ie the aircraft is actually flying 750 ft lower than the altitude indicated on the altimeter.
Note: Pressure Altitude is indicated on the altimeter when the barometric scale is set to the atmospheric standard of 1013 MPa or 29.92 inches of Mercury. (ie air pressure at MSL on an ISA day). If aircraft is flying at 12500 ft @ OAT of -20C and altimeter set at 30.42 inches of mercury. Rotate the barometric scale on the altimeter to 29.92 you will note a pressure altitude of only 12000 ft.
Finding Density Altitude given pressure altitude and OAT.
EXAMPLE:
Flying at 10000 ft pressure altitude with OAT of -20C; what is the density altitude?
1. Place -20C over 10000 ft pressure altitude on the "FOR TAS AND DENSITY ALTITUDE" window.
2. Refer to the density altitude window and find the answer of 8000 ft. Therefore density altitude is LOWER than pressure altitude.
Note: Density altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation. "Density Altitude" is the pressure altitude adjusted for non-standard temperature.
Both an increase in temperature and humidity will cause a reduction in air density. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
Use calculator side of the computer.
1. Align altitude and air temp in the small window "FOR TAS AND DENSITY ALTITUDE"
2. Locate the IAS on the "B"scale (inside scale) . The "B" scale is labeled as "CAS" which for practical reasons is the same as IAS.
3. Find the TAS on the "A" scale (outside scale) immediately above the IAS.
EXAMPLE:
What is the TAS under the following conditions: altitude 10,000 ft, temp -10 C; IAS 130 Kts?
Answer: 150 Kts
Finding True Altitude given indicated altitude and pressure altitude.
EXAMPLE:
Pressure altitude is 7000 ft, Indicated altitude is 6500 ft (on the altimeter), temp is -10C, what is the true altitude?
Locate -10C and Pressure Altitude of 7000 ft on the "FOR ALTITUDE COMPUTATIONS" window. From the "B" scale and locate the Indicated Altitude of 6500 ft. Look directly over this value and find the true altitude is 6250 ft.
At a Pressure Altitude of 7000 ft, and an indicated altitude of 6500 ft the TRUE ALTITUDE is actually 6250 ft ie the aircraft is actually flying 750 ft lower than the altitude indicated on the altimeter.
Note: Pressure Altitude is indicated on the altimeter when the barometric scale is set to the atmospheric standard of 1013 MPa or 29.92 inches of Mercury. (ie air pressure at MSL on an ISA day). If aircraft is flying at 12500 ft @ OAT of -20C and altimeter set at 30.42 inches of mercury. Rotate the barometric scale on the altimeter to 29.92 you will note a pressure altitude of only 12000 ft.
| Pressure Altitude ft | Static Pressure kPa |
|---|---|
| 0 | 101.325 |
| 1000 | 97.715 |
| 2500 | 92.500 |
| 5000 | 84.306 |
| 10000 | 69.681 |
| 20000 | 46.563 |
| 30000 | 30.089 |
| 36090 | 22.631 |
Finding Density Altitude given pressure altitude and OAT.
EXAMPLE:
Flying at 10000 ft pressure altitude with OAT of -20C; what is the density altitude?
1. Place -20C over 10000 ft pressure altitude on the "FOR TAS AND DENSITY ALTITUDE" window.
2. Refer to the density altitude window and find the answer of 8000 ft. Therefore density altitude is LOWER than pressure altitude.
Note: Density altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation. "Density Altitude" is the pressure altitude adjusted for non-standard temperature.
Both an increase in temperature and humidity will cause a reduction in air density. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
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